hdpe drainage pipe a thesis - tdl

CONSTRUCTIBILITY REVIEW AND ECONOMIC ANALYSIS

FOR THE INSTALLATION OF LARGE-DIAMETER

HDPE DRAINAGE PIPE

by

MOHAMMED DIDARUL ALAM, B.E.

A THESIS

IN

CIVIL ENGINEERING

Submitted to the Graduate Faculty of Texas Tech University in

Partial Fulfillment of the Requirements for

the Degree of

MASTER OF SCIENCE

IN

CIVIL ENGINEERING

Appr£)ved

ClVaic^er^bn of the Committee

Accepted

uean of ±he Graduate School

/august, 2000

ACKNOWLEDGEMENTS

The research project with regard to this thesis was sponsored by Texas

Department of Transportation. I would like to show my appreciation to all TxDOT

officials who made the decision to provide support for conducting this research.

I express my deepest gratitude to my advisor. Dr. Priyantha Jayawickrama,

Associate Professor of Civil Engineering, for his guidance. This work would not be

possible without the tremendous effort put by him.

I am thankful to Dr. Sanjaya Senadheera for kindly serving as a member of my

thesis committee. I am truly indebted to Dr. Doug Gransberg, Professor of Engineering

Technology for providing his precious suggestions while conducting the research for this

thesis. Special thanks is extended to Dr. Scott Phelan, Research Associate Professor of

Civil Engineering, for his valuable contribution in the research regarding this thesis.

I consider myself to be extremely fortunate to have some good friends who

encouraged me to complete this thesis with reassuring inspiration and help.

11

TABLE OF CONTENTS

ACKNOWLEDGEMENTS ii

ABSTRACTS vi

LIST OF TABLES vii

LIST OF FIGURES ix

CHAPTER

1. INTRODUCTION 1

1.1 General Introduction 1

1.2 Constructibility: General Overview 2

1.3 Economic Analysis: General Overview 3

2. LITERATURE REVIEW 5

2.1 Introduction 5

2.2 Approaches in Practice for Constructibility Review 6

2.3 Constructibility Approach Suggested in NCHRP Report 391 6

2.3.1 Constructibility Review: Its Definition 7

2.3.2 General Purposes and Benefits of Constructibility Review 8

2.3.3 Appropriate Time to Apply Constructibility Review 9

2.3.4 Level of Formalizing Constructibility Review 9

2.3.5 Process Approach to Constructibility Review 11

2.3.5.1 Proj ect Development Process (PDF) Framework 11

2.3.5.2 Consctructibility Review Process (CRP) Framework... 12

2.3.5.3 Integration ofCRP into PDF 12

2.3.6 Constructibility Review Tools 14

2.4 Army Corps of Engineers' Approach for Constructibility Review 14

2.4.1 Introduction 14

2.4.2 Definitions and Purposes of BCOE Review 16

2.4.3 Guidelines for implementing BCOE review 16

2.4.4 Responsibilities Involved with Issuing A Certification for Finalized BCOE Review 18

111

2.5 Conclusions 18

CONSTRUCTIBILITY REVIEW 22

3.1 Constructibility Review Team 22

3.2 Development of the Work Breakdown Structure (WBS) 23

3.3 Equipment 24

3.3.1 Trench Excavators 24

3.3.2 Trench Support System 30

3.3.1.1 Drag Box 31

3.3.1.2 Trench Box 31

3.3.3 Earth Moving Equipment 36

3.3.4 Compaction Equipment 36

3.3.5 Weight of Equipment 37

3.4 Deficiencies in Draft Specification 40

3.5 Minimum Trench Width Requirements 40

3.6 Types of Backfill Materials 45

3.7 Granular Backfill Gradation 46

3.8 Minimum Cover 47

ECONOMIC ANALYSIS 50

4.1 Overview 50

4.2 Review of Information from Other States 53


4.2.2 Economic Impact from the Acceptance of HDPE as a Biddable Altemative 54

4.3 Comparison of HDPE and RCP As-installed Cost Based on Analysis Performed with 'PipePac 2000' 59

4.4 Economics: State of Texas 60


4.4.2 Pipe Price 63

4.4.3 Backfill Material Price 65

4.4.3.1 Overview 65

IV

4.4.3.2 Data Collection 69

4.5 As-installed Costs ofHDPE and Concrete Pipe 78

4.5.1 Sources of Data and Assumptions Made for Model Project Analysis 79

4.5.2 A Comparative Review on Findings of Model Project Estimation for Competing HDPE and RCP 81

5. CONCLUSION 91

5.1 Introduction 91

5.2 Conclusions 92

5.2.1 Conclusions: Constructibility Review 92

5.2.2 Conclusions: Economic Analysis 93

5.3 Recommendations 94

LIST OF REFERENCES 96

APPENDICES

A. DRAFT SPECIFICATION DATED MAY 1998 98

B. REVISED SPECIFICATION DATED AUG 1999 104

C. TYPES OF BACKFILL MATERIAL ECONOMICALLY AVAILABLE IN THE DISTRICTS OF TEXAS I l l

D. WORK BREAK-DOWN STRUCTURE: ITEMIZING MAJOR ACTIVITIES 115

E. ESTIMATING AS-INSTALLED COST OF HDPE AND RCP PIPE 121

ABSTRACT

This thesis documents the findings from a constructibility review and an

economic analysis for the installation of large diameter High Density Polyethylene

(HDPE) pipe for gravity flow storm drainage. Pipes of diameter 18 in., 24 in., 30 in., 36

in., 42 in. and 48 in. have been considered in the above analysis. The constructibilty

review and the economic analysis described here were performed as a part of a research

project that was sponsored by Texas Department of Transportation (TxDOT). A draft

specification was developed for HDPE pipe installation as the primary objective of the

above research project. Deficiencies in several areas of the draft specification were

figured out through a formal constructibility review approach that have been documented

in this thesis. Revised recommendations are incorporated into the final specification on

four areas: minimum trench width requirements, addition of cement stabilized backfill as

a new backfill type, gradation requirements for granular backfill, and minimum cover

requirement above the pipe crown. Large-diameter HDPE pipe is prone to flexural

deflection and it withstands the load exerting on it by the structural integrity of the pipe-

soil systerm. Revised recommendations were made with a view to conduct high quality

installations with HDPE pipe with suitable backfill materials. Any quality improvement

though constructibility review involves extra money. Therefore, the economic analysis

part of this thesis analyzed the economics ofHDPE pipe installation projects with respect

to installation with other traditional pipe products, such as RCP and CMP. The analysis

resulted in a comparative picture between HDPE and RCP from the viewpoint of

economics. However, all the cost figures used in this analysis were present value of the

resources. Significant savings was estimated from using HDPE over RCP under many

resource availability conditions. Despite the stringer installation requirements ofHDPE

pipe compared to RCP, analysis of data from real projects and hypothetical projects

showed that HDPE pipe can be cheaper if some locally available suitable backfill

material can be procured to the project site at a reasonable cost.

VI

LIST OF TABLES

3.1 Constructibility Review Team 23

3.2 Itemizing Major Activities 25

3.3 Minimum Digging Depth 30

3.4 Backhoe's Operating Weight 31

3.5 Equipment weight 39

3.6 Minimum Trench Width Recommendation in Various Specifications and Suggested by Various Pipe Manufacturers 42

3.7 Minimum Trench Width to Use Compactors 44

3.8 Minimum Trench Width 44

3.9 Gradation Requirements for Type III Backfill Material 47

4.1 Impact on Average Unit Bid Price of RCP when HDPE was Permitted to Bid as Experienced by SCDOT, 1996-1997 55

4.2 As-installed Cost Comparison for Different Pipe Materials 57

4.3 Percent Saving due to Presence of HDPE in the Bidding Process 59

4.4 As-installed Cost ofHDPE and RC Pipe Estimated by Using 'PipePac 2000'

and Savings from HDPE 62

4.5 Typical Smooth Interior Wall Corrugated HDPE Pipe Pricing (May, 1999)... .63

4.6 1998 Price of ASTM C-76 Class III RC Pipe (Supplied from San Antonio Plant, Manufacturer I) 66

4.7 Price of ASTM C-76 Class III RC Pipe (Supplied from Dallas/Fort Worth Metro Area Plant, Manufacturer I) 66

4.8 Price of ASTM C-76 Class ffl RC Pipe (Supplied from Dallas/Fort Worth Metro Area Plant, Manufacturer II) 67

4.9 Delivery Zones by County (Deliveries from Dallas/Fort Worth

Plant ofRCP Pipe, Manufacturer II) 67

4.10 Economically Available Granular Material in Texas 71

4.11 Overall Average Bid Price of Flowable Fill in Texas Districts, 1999 72

4.12 Overall Average Bid Price of Cement Stabilized Backfill in Texas Districts in 1999 74

4.13 Different Price Category of Cement Stabilized Backfill in Different Parts of Texas 75

vii

4.14 Overall Average Bid Price of Flex Base 77

4.15 Suitable Backfill Materials Selected for HDPE Pipe As-installed Cost Estimation 78

4.16 Estimated As-installed Cost of HDPE and RCP 84

4.17 Percent Estimated Saving from Using HDPE 89

C. 1 Types of Backfill Materials Economically Available in the Districts of Texas 112

D. 1 Work Breakdown Structure: Itemizing Major Activities of Pipe Installation Projects 116

E.l Estimating As-installed Cost ofHDPE and RC Pipe 122

Vlll

LIST OF FIGURES

2.1 The Effect on Cost due to Incorporating Constructibility Review at Different Stages of Project Life Cycle 10

2.2 First Two Levels of Typical PDP Framework 13

2.3 First Two Levels of Typical CRP Framework 13

2.4 Incorporating CRP into PDP 15

2.5 Items Addressed for Biddability and Constructibility 20

2.6 Items Addressed for Operability 20

2.7 Sample of BCOE Certification 21

3.1 Flowchart for Selection of a Trench Support System 32

3.2 Drag Box Installation 33

3.3 Trench Box Module 33

3.4 Pipe Installation with Trench Boxes 34

3.5 Pipe Installation with Slide Rails 35

3.6 Vibratory Plate Compactor and Impact Rammer 38

3.7 Comparison of Some of the More Commonly Used Trench Width Guidelines 43

3.8 Excerpts from Draft Specification that Address Minimum Cover Requirements 49

4.1 Percent HDPE Pipe Used by NY State DOT in Recent Years 61

4.2 Unit Pipe Price Comparison in Texas: HDPE versus RC Pipe 68

4.3 Price Zones of Cement Stabilized Backfill in Texas 76

4.4 As-installed Cost of RCP at Varying Pipe Price Conditions 85

4.5 Estimated As-installed Cost of HDPE versus As-installed Cost of RCP For Different Resource Price Conditions 86

4.6 Estimated As-installed Cost ofHDPE versus As-installed Cost of RCP For Different Resource Price Conditions 87

4.7 Estimated As-installed Cost ofHDPE versus As-installed Cost of RCP For Different Resource Price Conditions 88

IX

CHAPTER 1

INTRODUCTION

1.1 General Introduction

This thesis documents the findings from a constructibility review and an

economic analysis for the installation of large diameter High Density Polyethylene

(HDPE) pipe for gravity flow storm drainage. Pipes of diameter 18 iiL, 24 iiL, 30 irt, 36

iiL, 42 in. and 48 in. have been considered in the above analysis. The constructibilty

review and the economic analysis described here were performed as a part of a research

project that was sponsored by Texas Department of Transportation (TxDOT). The

primary objective of the above research project was to develop standard specifications for

the installation of large diameter High Density Polyethylene pipe for gravity flow storm

drainage. In 1993, TxDOT introduced special specification No.4296: "Thermoplastic

Pipe" (1993) that enabled the use ofHDPE pipe of up to 36 inch diameter in TxDOT

construction projects. Because HDPE is flexible pipe, its performance criteria are

different from those of rigid pipe. The strength of flexible HDPE pipe is the result of the

pipe-backfill integrated system, whereas concrete pipe withstands most of the imposed

loads because of its rigid structural strength. Due to these special characteristics of the

HDPE pipe-soil system, a high quality installation, specifically proper backfilling around

the pipe, needs to be assured. Therefore, as a means of quality control during the

installation of thermoplastic pipe, it is customary to measure pipe deflection after its

uistallatioiL However, OSHA requirements for confined space safety prohibit

departmental or contractor personnel entering pipe to measure deflectiorL TxDOT

special specification No. 4269 allowed the use of two types of backfill materials in the

pipe embedment zone; Type I: Flowable backfill and Type II: Granular backfill.

However, in March 1996 TxDOT decided to remove the requirement to measure pipe

deflections and at the same time decided to require flowable backfill in all installations

regardless of the location with the exception of side roads and driveway culverts (Source:

Special Provision and/or Specification Change Memorandum from Wilson, Robert, dated

March 15, 1996). Unfortunately, flowable fill is the most expensive of all backfill

materials. Consequently, when flowable fill was used, the high cost of backfill ofl&et any

economic benefits that could have been gained by using comparatively cheaper HDPE

pipe. This situation led TxDOT to initiate a comprehensive research study with the

specific objective of finding alternate, cheaper backfill materials for HDPE pipe

installation. Research work was completed during the initial phase of the above research

project (i.e., from September 1997 to May 1998) resulted in a draft specification that

documented recommendations for a quality installation ofHDPE pipe v^th diameter

ranging from 18 in. to 48 in. This draft specification, dated May 15, 1998 is found in

Appendix A of this thesis. The next step in this research was to perform constructibility

review on the above draft specification to ensure that the pipe installation according to

the specification can be accomplished in the field v^thout difficulty. Difficulties can

arise during the field implementation due to ambiguities in the specifications, contractors'

lack of familiarity with construction methods specified, non-availability of special

construction equipment required, non-availability of specified material within economic

distances, levels of quality that are unrealistically high to be achieved in the field, etc.

The various steps taken in completing the above constructibility review is fiilly described

in this thesis. Constructibility review, which is one of the two key topics of this thesis,

involves quality eissurance during HDPE pipe installation. Secondly, one of the primary

incentives for the use ofHDPE pipe is the economic benefit to be gained from the

cheaper material cost as well as faster installation. However, on the other hand, this type

of pipe requires special types of backfill materials other than native soil and therefore

must be obtained at a cost. Therefore, economics of pipe installation is an irr^rtant

aspect that must be examined in the selection of backfill materials. Accordingly, the

second topic that is addressed in this research involved a detailed economic analysis

related to HDPE pipe installation in Texas. The followdng two sections provide a general

overview of this project-specific constructibility review and economic analysis. They

also describe how the other remaining chapters of this thesis have been organized.

1.2 Constructibility: General Overview

Once the importance of performing a constructibility review for the HDPE pipe

installation was acknowledged by the researchers, then it was necessary to prepare a work

plan to accomplish this task. As a first step toward the goal, the existing formalized

approaches for detailed constructibility review were examined as a part of the literature

survey. The findings from this task are documented in Chapter 2 of this thesis. Based on

the above literature survey, constructibility strategy for HDPE pipe installation was

begun. The first step in this process was to form a constructibility review team. The

entire constructiblity review is described in detail in Chapter 3. The input needed for

constructibility was obtained through a number of sources. Contractors who are

experienced with this kind of pipe installation project were contacted in order to receive

input from their professional experience. Members of the TxDOT project monitoring

committee also made inq)ortant contributions to this process by pointing out some

implementation ambiguities in the presented draft specification. Eight TxDOT pipe

installation projects that were located in difierent districts of Texas were selected and

their installations and post-construction performance were monitored throughout the

project duration. Additionally, observations from a series of on-campus tests were used

in constructibilty review.

An important objective of this research was to find alternate backfill materials in

order to avoid using flowable fill. The gradation characteristics of several granular

backfill materials have also been examined in Chapter 3 as a part of this constructibiltiy

review. The suggestion from district laboratory engineers was the primary source of

information on readily available backfill materials in Texas. A revised specification

dated August 16, 1999, included all the modified recommendations on trench dimensions

and backfill materials that was obtained through constructibility review performed in

Chapter 3. This revised specification is found in Appendbc B of this thesis.

1.3 Economic Analysis: General Overview

One of the important issues related to the acceptance of HDPE pipe as a biddable

altemative for large diameter storm drainage systems is whether HDPE pipe can compete

economically against two other pipe products that have been in use in construction for

many years, namely reinforced concrete pipe and corrugated metal pipe. Since it is

important to ensure a very good quality pipe-soil structural system when installing HDPE

pipe, its installation generally requires more expensive backfill materials and extra care

during backfilling. The draft specification does not allow the native soil as backfill

material for HDPE pipe, whereas reinforced concrete pipe can be backfilled by native soil

without spending any extra money for purchasing and transporting special backfill

material. This is an important cost issue involved in installation of HDPE pipe. On the

other hand, price of concrete pipe or corrugated metal pipe delivered at the site is much

higher than that of HDPE pipe. Also, handling the heavier concrete pipe involves more

labor and longer project duration compared to the lighter HDPE pipe. Longer project

duration involves extra cost. Thus, each kind of pipe material has relative advantages and

disadvantages from an economic point of view. In Chapter 4 of this thesis, all the factors

affecting the cost of the pipe installation are discussed in great detail. In this chapter an

economic analysis was performed to compare HDPE pipe with reinforced concrete pipe

and corrugated metal pipe from the standpoint of installation cost. Chapter 4 begins with

information that were collected from others state DOTs providing a comparative

overview of as-installed costs for HDPE pipe versus other pipe products. Secondly, the

price information for various resources involved with pipe installation, specifically the

price of backfill material and the price ofHDPE and reinforced concrete( RC) pipe within

various parts of Texas are documented. For this purpose, leading manufacturers and

suppliers of the resources were contacted through phone, fax and email. This information

is presented in Chapter 4 in a comparative manner. It shows the availability and

comparative price of important resources involved in HDPE pipe installation, as well as

installation with other competing pipe materials, specifically in Texas districts. With the

help of this actual resource price information, as installed costs of several model projects

(using HDPE and RC pipe) have been calculated. The estimates of those model projects

were synthesized parametrically. The three parameters chosen were pipe diameter, pipe

price and backfill material price in different districts of Texas.

CHAPTER 2

LITERATURE REVIEW

2.1 Introduction

The importance of incorporating constructibility review into the processes of

HDPE pipe installation was introduced briefly in Chapter 1. As a continuation of that

introduction on constructibility review, this chapter mainly discusses available

approaches for project level constructibility review as a part of the literature review for

this thesis. Prior to starting on the approaches in practice for constructiblity review, this

section examines why HDPE pipe installation projects need a formal approach for

construcitiblity assessment. Consequently the following sections drew focuses on

available literature about formal approaches of constructibility review.

Constructibility review is a very recent concept. It was previously conceived as

an informal approach for improving project development process until a few years ago.

Most projects have some kind of informal constructibility review that does not follow any

well-organized review pattem or incorporate any constructibility review persoimel. But

when a big budget project has alternatives in the context of choosing various resource

options based on performance and economy, a formalized approach may be a key-tool for

successfully implementing a project using certain preferable resources. In the previous

chapter it was revealed that HDPE pipe has two other broadly accepted altemate pipe

materials that creates a competitive environment for large diameter gravity flow storm

drainage pipe installation projects. These are Reinforced Concrete Pipe (subsequently

referred to as RCP) and Corrugated Metal Pipe (referred to as CMP). One vital point

about using different pipe materials is that the construction processes that involve the

installation with different kinds of pipe are not all the same. Hence, developing a new

specification for installation of large diameter HDPE pipe was the leading part of this

research project. In the process of developing that specification it was perceived by the

researchers that construction processes ofHDPE pipe installation are critical to some

extent compared to that of other pipe, such as RCP and CMP. This is because of flexural

nature of large diameter HDPE that might cause flexural deflection in future. The

researchers finally came up with performing a constructibilty review that was performed

on the draft specification rather than on any specific construction projects. The following

sections, perceptively, skimmed though the relevant literatures on constructibility review.

2.2 Approaches in Practice for Constructibilitv Review

Among the existing approaches a comprehensive model for formalized

constructibility review is suggested in the NCHRP report 391, "Constructibility Review

Process for Transportation Facilities," prepared by Anderson and Fisher (1997). Another

approach practiced by the U.S. Army Corps of Engineers supports the BCOE

(biddability, constructibility, operability, and environmental review) aspects of a project

(USAGE, 1994). In order to incorporate a formalized constructibility review approach

into HDPE pipe installation, and to set up objectives and plans for it, botii

constructibility approaches will be discussed here as a part of the literature review for this

thesis.

The following two sections summarize the ideas and guidelines presented in

these two models.

2.3 Constructibilitv Review Approach Presented in the NCHRP Report 391

NCHRP Report 391, "Constructibility Review Process for Transportation

Facilities," is a formal and comprehensive project level workbook for performing

constructibility review. This model will be presented here as a part of essential literature

review for this thesis that will lead us to incorporate some concepts of this model into the

constructibility review process ofHDPE pipe installation projects. The main objective of

this workbook is to show guidelines on how to improve highway-construction-project

contract documents, to ensure rational bids and to minimize problems during

construction. The workbook contains two stand-alone sections. The user of the book

might want to choose any or both the sections as a background depending on the

characteristics of the project needed to be reviewed. Presumably, HDPE pipe installation

projects have their ovm project level difficulties that might arise during its construction

phase because of the flexural nature of lightweight HDPE pipe. Section I illustrates the

framework of constructibility review process presented in this workbook. Section II

demonstrates implementation details of constructibility review process. However,

Section I, the overview, was of prime interests for this research in order to set up a plan

for constructibility review ofHDPE pipe installation. The whole concept presented in the

workbook is summarized here under some key-phrases and only those parts of it is

presented with emphasis which might be helpful to figure out a plan for the

constructibility review ofHDPE pipe installation. More specifically, the key-concept of

this formal and comprehensive approach for constructibility review is how a Project

Development Process (PDP) interacts with and gets benefited from the Constructibility

Review Process (CRP). In any way, the particulars of constructibility review guidelines

presented in this workbook can be described under the following terms.

a. Constructibility review: its definition;

b. General purposes and pay backs of constructibility review;

c. Appropriate time to apply constructibility review;

d. Level of formalizing constructibility review;

e. Process approach to constructibility review;

f Constructibility review tools.

The following sections will reveal that inherent concept of this formalized

constructibility review model.

2.3.1 Constructibilitv Review: Its Definition

Constructibility review is defined in the NCHRP Report 39las follows:

"Constructibility is integration of construction knowledge and experience in

planning, design, procurement and field operations to achieve overall project objectives"

This definition simply means that constructibility review is the integration of

construction knowledge and experience into planning, design and construction phases of

a project. Report 391 emphasizes on looking for and apply construction knowledge and

experience and to store this information in an appropriate format for easy retrieval. This

is a proactive mechanism that will improve outputs of planning and design processes and

end up with efficiency of construction. Constructibility practices should be made an

integred part of the project development process through some level of formalization.

2.3.2 General Purposes and Benefits of Constructibilitv Review

If construction knowledge and experience can be incorporated into an improved

project development process through constructibility review, generally it can bring the

following benefits:

a. Reduced costs,

b. Shortened schedule,

c. Improved project quality and safety,

d. Enhanced management of risk,

e. Increased customer satisfaction,

f Constructibility pays for itself.

Implementation of constructibility requires extra time, money and people.

Evidences indicate that constructibility pays for itself by reducing project costs. In 1992,

the Arizona DOT established a Constructibility Engineer position. This person has an

extensive background both in design and construction. Plans and specifications are

reviewed by this person to determine possible improvements from a constructibility

perspective. The savings achieved as a result of constructibility improvements amoimted

to 1.7% of the total cost of the six projects (approximately $68 million). The expense of

the review was such that the benefit to cost ratio was twenty five to one. That is, for

every dollar spent reviewing these projects for constructibility, Arizona DOT saved $25.

Additional benefits identified in Report 391 can be quoted here as follows:

a. Engineers, through constructibility review programs, can be trained more

quickly, thus providing better decision-making, support data and knowledge.

b. The probability of successful project schedule performance increases

substantially with a formal constructibility program especially on fixed-price

contracts.

c. The intangible benefits which include higher productivity, better schedules and

sequence of construction, enhanced quality, lower maintenance, safer jobs, and

more safety and convenience for the traveling public should also be recognized.

2.3.3 Appropriate Time to Apply Constructibilitv Review

Fig 2.1 demonstrates a very important and observable criteria that has to do with

appropriate timing of applying constructibility review. In the life cycle of a project

implementation a project usually goes though the general steps of planning, design,

bidding, pre-construction meeting, construction, operation and maintenance. Fig. 2.1

shows that maximum benefit can be achieved if the effective use of construction

knowledge and experience can be incorporated during the early stages of planning and

design. This is because the ability to influence cost through changes in project plans and

design is maximum during these early stages. The research proposal for developing a

new specification for HDPE pipe installation, advantageously, had included the idea of

performing constructibility review well ahead of the time when the research started.

Unfortimately, agencies seem to rely heavily on the construction expertise of

design personnel, who are well versed in such technical issues as design standards and

codes, but who lack expertise in field construction methods and techniques. This

approach reduces the likelihood of getting benefits from applying constructibility review

at the appropriate time. This is actually an informal approach of performing

constructibility review conceived by most transportation agencies. The section below is

about level of formalization required when applying constructibility process.

2.3.4 Level of Formalizing Constructibility Review

Depending on project complexity, constructibility review process can be

categorized into three level of formalization : Informal, semiformal and formal.

Constructibility is given minimal attention during project planning and feasibility during

design reviews. Construction expertise is frequently not accessed during the plarming

and design process. The research associated with the development of the NCHRP Report

391 shows that only 23 percent of state agencies have formal, documented

constructibility programs. Also, the level of formality of these programs varies. Several

programs are somewhat formal, as they incorporate constructibility concepts suggested in

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the literature such as specifying constructibility objectives, forming a constructibility

team, determining the level of formality, and mechanisms to obtain constructibility input.

Less formal programs often use checklists, with input obtained only at definite points in

the design process where reviews take place. While interest in formalizing

constructibility reviews is growing, even the most formal constructibility programs

appear to lack distinct functions and steps that lead the project personnel through

implementation process. Formalization of the Constructibility Review Process

(designated as CRP) must tap the right expertise and information when and where needed

to achieve maximum benefits.

2.3.5 Process Approach to Constructibility Review

A process approach to implementing constructibility at the project level is

presented in the NCHRP Report 391. This approach consists of describing the process at

a microscopic scale, ultimately focusing on functions, steps and tools essential to conduct

a project level Constructibility Review Process (CRP). At this level CRP acts on outputs

from the Project Development Process (PDP) in order to provide constructibility

improvements that are incorporated into planning and design docimients. In the

following sections CRP and PDP will be defined and incorporated together to create the

skeleton for constructibility review.

2.3.5.1 Proj ect Development Process (PDP) Framework

Projects are developed through a process described as the Project Development

Process which typically consists of three main phases:

1. Planning

2. Design

3. Construction

Each phase is further divided into an increasing level of detailed activities. This

continuing breaking down of a project into several levels of hierarchy makes the PDP

frame work. The activities at upper levels of the framework are considered generic and

are typical of most project development processes. However every state agency will have

11

its own unique PDP. The first two levels of a typical PDP framework have been shovm

in Fig. 2.2 by branching each phase into sub-phases and each sub-phase into more

detailed project activities that involve specific man power, equipment, and other

resources. For example. Preliminary Design, a sub-phase of Design Phase presented in

Fig. 2.2, has been divided into eight detailed project functions at the third level of the

framework. In the same manner, other sub-phases of three major phases of PDP

framework needs to be divided into relevant activities. This third level of the framework

is of prime interest from the viewpoint of constructibility review where necessary

modification and improvement can be made to achieve project goals.

2.3.5.2 Consctructibility Review Process (CRP) Framework

CRP is applied during the planning, design, and construction phases of a project.

Quite analogous to PDP framework described in the previous section, the CRP is divided

into increasing levels of detailed constructibility functions. As outlined in Fig. 2.3 the

first two levels of the CRP framework imitate the PDP phases and sub phases. The third

level which is derived from the second level of hierarchy represents the proposed

individual constructibility functions that are performed during project development.

This level is where activities occur in order to integrate construction knowledge

and experiences into the PDP. In Fig 2.3 only 'Design Phase' has been divided into

detailed constructibility functions at the third level of the framework. In a similar

fashion other two major phases. Planning Phase and Construction phase, can be

disintegrated into detailed constructibility functions up to the third level in the

framework.

2.3.5.3 Integration ofCRP into PDP

As shovm in Fig. 2.4, integration of construction knowledge and experience into

the PDP necessitates iterative, recursive exchange of information between the PDP and

the CRP. Project information from PDP flows to CRP, which then takes this

information, acts on it, and retums suggested improvements for incorporation into

planning and design. Each set of constructibility functions has a specific objective. To

12

AOP: Project Development Process AlP: Planning Phase

A l lP : Project Definition A12P: Concept Plan Development

A2P: Design Phase A21P: Preliminary Design

A211P: Design Criteria/Para meters A212P: Survey Utilities/Locations/Drainage Area A213P: Design Concept/Conference A214P: Geotechnical Studies A215P: ROW Development A216P: Geometric Alignment A217P: Bridge Layouts A218P: Permits/Agreementa

A22P: PS&E Development A23P: Final Design

ASP: Construction Phase A31P: Pre-Construction Phase

A32P: Construction A33P: Post-Construction

Fig. 2.2: First Two Levels of a Typical PDP Framework.

(Source: Anderson and Fisher(1997), NCHRP Report 391. pp. A0.8)

AO: Apply Constructibility to Transportation Projects A l : Apply Constructibility during Planning Phase

A l l : Apply Constructibility during Project Definition A12: Apply Constructibility during Concept Plan Development

A2: Apply Constructibility during Design Phase A21: Apply Constructibility during Preliminary Design

A211: Modify Constructibility Team A212: Finalize Project Constructibility Procedure A213: Consult Lessons Learned to Design

A22: Apply Constructibility during PS&E Development A221: Evaluate Plans &Speciflcations A222: Validate Constructibility Improvement A223: Review and Approve Constructibility Improvements

A23: Apply Constructibility during Rnal Design A224: Summarize Constructibility Improvements

A3: Apply Constructibility during Construction Phase A31: Apply Constructibility during Pre-Construction Phase A32: Apply Constructibility during Construction A33: Apply Constructibility during Post-Construction

Fig. 2.3: First Two Levels of a Typical CRP Framework.

(Source: Anderson and Fisher(1997), NCHRP Report 39 L pp. A0.9)

13

achieve these objectives, inputs from the PDP and from a preceding set of

constructibility functions are essential. In the same manner, outputs from performing

each set of constructibility functions return information to the PDP and to the next set of

constructibility functions. This cyclic process between the CRP and PDP continues as

long as the project proceeds through each phase. Fig. 2.4 illustrates the basic structure

of implementation guidelines for constructibility review presented in the NCHRP Report

391.

2.3.6 Constructibility Review Tools

NCHRP report 391 lists a set of constructibility review tools and describes their

characteristics and usage recommended to perform individual actions for each

constructibility functions. Future tools, that is, those tools having potential applications

in the future for an advanced CRP, are also listed. Some of these tools are listed below.

a. Constructibility meetings

b. Suggestion forms

c. Pre-bid conference

d. CPM (critical path method)

e. Benefit-cost analysis, etc.

2.4 U.S. Army Corps of Engineers' Approach

2.4.1 Introduction

U.S. Army Corps of Engineers (1994) established a regulation No. 415-1-11 titled

as 'Biddability, Constructibility, Operability and Environmental (BCOE )' in the

regulation no. 415-1-11. It has been docimiented in 8 sections. Section 1, 2, 3 and 4

describes the purposes, applicability, references used, and definitions respectively

concerning the BCOE aspects presented in this regulation. Section 5 briefly gives a

general overview of the concept. Section 6 occupies major portion in this regulation that

illustrates the implementation guidelines of BCOE aspects. Section 7 and 8 specifically

lists the designations of appropriate personnel and their responsibilities needed to make

BCOE review official and issue certification.

14

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BCOE concept established by U.S. Army Corps Of Engineers has been presented

in the subsequent sections under the following sub-titles.

a. Definitions and purposes of BCOE review,

b. Guidelines for implementing BCOE review,

c. Responsibilities involved in making BCOE review official.

2.4.2 Definitions and Purposes of BCOE Review

The terms of BCOE aspects followed by U.S. Army Corps Engineers (1994) are

defined as follows:

Constructibilty and biddability are defined as ease with which a designed project

can be built and the ease with which the contract documents can be imderstood, bid

and, administered and executed. Operability refers to the ease with which a project

ca be operated and maintained. Environmental review refers to the protection of

air, water, land, animals, plants and other natural resources from the effects of

construction and operation of the project as stated in the Environmental Impact

Statement or Assessment.

The above definition of constructibility and biddability suggests to make the

contract documents comprehensive enough after the review is done so that it can be bid,

administered and implemented with clarity. Definitions of operability and environmental

review demonstrate their general purposes as stated above.

In short the purpose of this regulation is to consider BCOE aspects during design

and integrating a high degree of BCOE review into construction procurement for aU

projects.

2.4.3 Guidelines for Implementing BCOE Review

This is the kernel part of the BCOE concepts that is divided into three sub

sections: The following paragraphs briefly present the contents of this three sections.

Section 6(a) demonstrates the guidance to perform a BCOE review. This section

describes how to incorporate reviews at diSerent stages of a project by maintaining

proper timing and assuring that right person is involved in the review process. The

16

ultimate goal of BCOE review described in this section is to prepare a review document

that will serve as the basis for the certification required as stated in section 7 of the

regulation. People required for reviews and to improve BCOE aspects of designs include

construction, engineering, project management, and operations personnel from division

and district offices. Constructions and operation personnel from districts who are familiar

with project location and site related problems and have the potential to understand

design assumptions and specification, shall participate in the reviews. Input from

construction and operation personnel is desirable during both the following stages of the

project.

a. Early enough in the design process to allow its incorporation during design

development.

b. After final design and coordination reviews when the entire contract document

is ready for advertisement, but sufficiently prior to advertisement to allow for

corrections.

Therefore, in order to ensure appropriate timing of review, a minimimi of two

specific reviews are required to be performed by these personnel. The first will be made

at the concept stage when design process cannot be stopped and after the design is

sufficiently complete for substantive comment. The second will be made at final design

stage with complete specifications including special clauses at least 30 days prior to

advertisement. An additional review will be required once the design is completed and

reviewed that will be released to the prospective bidders after an abeyance period of six

months. The area/resident office shall transfer the comments to design branch though the

Automated Review Management system (ARMS). A BCOE back-check review for

certification required by Section 7 of the regulation is required by Engineering and

Construction Division prior to bid opening. All necessary comments shall be incorporated

in that final check prior to include it in the bid package.

Section 6(b) addresses the probable items and fimctions to be undertaken in

biddability and constructibility reviews that are supposed to be performed by Area

Engineer, Resident Engineer and Construction Staff personnel. Fig. 2.6 is an extract

from original regulation of U.S Army Corps of Engineers that lists 11 items/functions

17

addressed for biddability and constructibility reviews. In a similar fashion section 6(c) of

the regulation presumably lists 10 items for operability reviews which is presented in

Figure 2.7 below as an excerpt form original regulation. However, the items to be

addressed for reviews will not be limited to the functions listed in these two sections.

2.4.4 Responsibilities Involved with Issuing Certification for Finalized BCOE Review

The following officials bear the responsibilities for the accomplishment of

finalized BCOE review and have the certification for it.

a. Chiefs of Project Management has two responsibilities: (i) to ensure that

sufficient time for the BCOE reviews illustrated in Section 6.a is included in the project

baseline schedule and (ii) to ensure adequate design funds for the success of BCOE

reviews in the baseline budget.

b. Chiefs of Engineers will provide documents for review and back check,

evaluate comments, and provide feedback on disposition of comments. The main

responsibilities can be quoted as follows from the original regulation:

c. Responsibilities of Chiefs of Construction can be quoted as follows:

"The Chief of Construction or a duly authorized representative. Branch Chief or

higher, will certify, in writing that all appropriate BCOE comments have been

incorporated in the bid documents or satisfactorily resolved and that feed back has been

provided to reviewers for all comments."

d. Figure 2.8 below is a sample certification required to be signed by the Chief

of Engineering Division and the Chief of Construction Division as described above. This

has been attached with the original regulation as Appendix A. As stated in the regulation,

"Chiefs of Contracting will ensure that bid opening is not made prior to the above

certification unless the contracting officer determines that it is in the best interest of the

government to award without incorporation of all comment."

18

2.5 Conclusions

This chapter presented the available literature on constructibility review which

will serve as a background for Chapter 3. Consequently, Chapter 3, which performs a

constructibility review on the draft specification, starts with planning a constructibility

review strategy. Some of the concepts for performing a formalized constructibility

review presented in the previous sections have been incorporated in to the constructibility

plan. One such concept perceived from two models presented here is that some

personnel with specific responsibilities are required to be involved in this kind of review.

Therefore, a constructibility review team with specific responsibilities was constructed as

a part of a formal constructibility review strategy. The concept of breaking down a

project into detailed project activities as stated in a previous section as PDP/CRP

framework was applied at the beginning of the review in Chapter 3. However, no

literature review has been provided for economic analysis conducted in Chapter 4. It was

actually performed with a generic approach based on present-value-cost-data.

19

b. Items to be addressed in biddability and constructibility reviews performed by the Area engineer, Resident Engineer, and Construction Staff personnel will include, but not be limited to: (1) Accurate depiction and adaptation of design structures and features to site conditions and

restrictions such as access, utility availability, drainage, storage, existing underground utilities and general configuration.

(2) Appropriateness of contract sequencing, relationship to other work, contract performance time, contractor quality control (QC), submittal requirements and network analysis system provision for the specific project.

(3) Adequacy of working area and storage space and access for all site contractors as well as provisions for coordination to preclude on-site conflicts.

(4) Clarity, simplicity and essentiality of the bid schedule. (5) Local availability of special materials and labor skills. (6) Have special installation requirements been addressed? (7) Are the drawings and specifications free form ambiguities? (8) Are essential details and proper verbiage included ? (9) Do the specifications address the impact of the construction on the environment? Is the

contractor required to submit an environmental plan addressing how he will mitigate water, air, soil and noise pollution?

(10) Do the drawing depicts the site environment? Will the project encroach upon wetlands or endangered species habitat? Is erosion control adequately addressed?

Fig. 2.6 : Items Addressed for Biddability and Constructibility

(Source: U S. Army Corps. Of Engineers (1994), Regulation No. ER 415-1-11, pp. 3)

c. Items of operability reviews to be addressed by the facilities engineer or responsible operations engineer personnel will include, but not limited to:

(1) Architectural compatibility with existing facilities and established base plan (2) Adequacy of size and configuration of proposed facilities to meet the expected function or

mission and inclusion of all necessary features (3) Compatibility of proposed installation and equipment with existing facilities for ease of

maintenance and replacement. (4) Adequate size of mechanical equipment and maintenance spaces to facilitate maintenance. (5) Ease of maintenance and upkeep of planning and landscaping. (6) Adequacy of position indicators on operating equipment. (7) Adequacy of periodic inspection capability and ability to accomplish periodic maintenance. (8) Provision of features for safe, efficient and economic operation including maximum energy

conservation. (9) Appropriate level of operation sensitivity and/or complexity. (9) Design provides for operations which will be environmentally safe.

Fig. 2.7: Items Addressed for Operability

(Source: U. S. Army Corps. Of Engineers (1994), Regulation No. ER 415-1-11, pp. 4)

20

SAMPLE CERTIFICATION

BCOE Certification

Project Tifle:

Specification Number:

Installation:

I certify that all appropriate biddability, constructibility, operability and environmental

comments received and reviewed by this office by (Date) have been

incorporated into the bid package. Feedback has been provided to reviewers for all

comments.

Date Chief, Engineering Division

Date Chief, Construction Division

Fig. 2.8 : Sample of BCOE Certification

(Source: U S. Army Corps. Of Engineers (1994), Regulation No. ER 415-1-11, pp. A-1)

21

CHAPTER 3

CONSTRUCTIBILITY REVIEW

The previous chapter presented a detailed discussion of constructibility review as

a concept and its applicability to general civil engineering field construction projects.

This chapter describes the application of these concepts to evaluate the practicality of the

draft specification that was developed previously in this research project. This draft

specification can be foimd in Appendbc A of this report. It was developed based on

guidance available through specifications developed by other agencies such as AASHTO,

ASTM and other state DOTs as well as data collected from experimental work conducted

in this research. The primary objective of constructibility review was to examine the

draft specification from a constructibility viewpoint and hence identify any elements in

the specifications that may create difficulties during its field implementation. The

various steps involved in the above constructibility review and the recommendations are

presented in the following sections.

3.1 Constructibility Review Team

As a first step in the constructibility review process, it was necessary to identify a

number of qualified individuals to serve on a constructibility review team. In a typical

field construction project, the constructibility review will be performed by individuals

who have significant field experience in the specific construction processes involved.

However, the constructibility review described here was difierent in a number of ways.

First, it did not involve a specific pipe installation project. Instead, it involved a new

specification that has been developed for such pipe installations. Secondly, the review

was performed as a part of a research project. Therefore, this constructibility review

team consisted of two groups of individuals: (1) members of the research team, (2)

individuals with experience in the field installation of HDPE pipe. The researchers

included: (a) research assistant charged with the primary responsibility of conducting the

constructibility review, (b) the research study supervisor of the study and (c) other key

investigators. The field construction personnel included (a) members of the TxDOT

22

project monitoring committee, (b) contractor representatives from TxDOT pilot

construction projects in San Angelo and Laredo districts and (c) representatives from

HDPE pipe manufecturing companies. The primary role of the researchers was to collect

necessary information from the field construction personnel, published literature, phone

survey, and latest estimating catalogs and then perform the review based on this data.

Table 3.1 below identifies the members of the constructibility review team.

Table 3.1 Constructibility Review Team

Researcher/s Field Personnel

Research Assistant TxDOT Project Director Mohd. D. Alam Victor Pinon, P.E.

Research Supervisor District Construction Engineers P.W. Jayawickrama, Ph.D.

Other Key investigators Representatives of the Contractors Involved in TxDOT D.G. Gransberg, Ph.D., P.E. Pilot Construction Projects S. Phelan, Ph.D., P.E.

Representatives from the HDPE Pipe Manufacturers

3.2 Development of the Work Breakdovm Structure (WBS)

Constructibility review begins with the development of a Work Breakdown

Structure (WBS) for the particular construction project. During this task, the pipe

installation process is analyzed in detail and each individual construction activity is listed

in a sequential manner. As a first step, the pipe installation process is divided into five

major tasks. They are:

1. Trench excavation,

2. Installation of trench support system,

3. Preparation of the trench bottom,

4. Laying and joining pipe,

5. Placement and compaction of backfill.

23

The next step involves the development of the detailed work breakdown structure.

In the detailed work breakdown structure, each task is divided into several sub-tasks.

Table 3.2 presents the above detailed work breakdown structure. It identifies all the steps

that the site engineer, contractor, and the construction crew must go through from the

time they receive the plans to the time of project completion. Table 3.2 also provides

information on the resources needed for the completion of each sub-task. These

resources include: equipment, construction crew and material. Subsequently, in Chapter

4 Economic Analysis, this work breakdown structure is fiirther expanded to include the

costs associated with each construction activity.

3.3 Equipment

As shovm in Table 3.2, one of the important resources needed for successful pipe

installation includes construction equipment. The construction equipment required for

each itemized work process, as listed in that table, include the following:

1. Trench excavators;

2. Trench support system: trench boxes, drag boxes, slide rails, trench sheeting;

3. Pipe-layers, cranes;

4. Backfilling equipment: loaders, backhoes, backhoe loaders;

5. Compaction equipment for initial backfill: vibratory plate compactors, impact

rammers;

6. Earth moving vehicles: elevating scrapers, belly-dump trucks.

The following sections provide a preview of the equipment listed above. The

discussion includes the selection of right type of equipment for each work process and

their effects on the installation process as a part of constructibility review

3.3.1 Trench Excavators

Backhoe is the most commonly used equipment for the excavation of pipe

trenches. It is used for excavating below the level of tracks and also as a small crane for

handling duties

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29

in pipe laying and installing trench support system. When excavating large and deep

trench, an operating plan should be sketched to suit the removal of the spoil and

accommodate any ramps needed for the trucks. Selecting an excavator of right capacity

is important to do the excavation job without any difficulty. Table 3.3 lists typical

maximum digging depth for hydraulic backhoes of varying capacity. Accordingly, the

maximum digging depth for a backhoe with % CY capacity is 18 ft (6m). In other words,

greatest construction efficiency may not be achieved if the above equipment is used to

excavate a trench with depth of say 25 ft (approximately 8m).

Table 3.3 Maximum Digging Depth

Bucket capacity y4CY-5/8CY y4 CY ICY 2 CY 2 CY 2'/2CY 3 CY (not heaped)

Backhoe's 5m 6m 7m 8m 8m 8!/2m 9m Maximum digging depth

Another important factor to be taken into consideration in the selection of the

appropriate excavation equipment is their operating weight. This is because any

equipment that traverses the already installed pipe has the potential to disturb the

structural integrity of buried HDPE pipe. This issue will be reviewed in a subsequent

section of this chapter where the minimum cover required for various axle loads. Table

3.4 below lists typical operating weights for backhoes of various capacity.

3.3.2 Trench Support Systems

Pipe installation projects may involve excavation to large depths. In such

projects, safety of the construction crew working inside the trench require special

attention. Safety must be ensured through the selection of a trench support system that is

appropriate for the specific depth of excavation.

30

Table 3.4 Backhoe's Operating Weight

Maximum bucket capacity Operating weight 0 . 8 2 C Y 27,910 lbs 0.97 CY 35,100 lbs 1.83 CY 50,000 lbs 2.12 CY 59,560 lbs 2.75 CY 73,880 lbs

3.40 CY 110,420Jlbs Source: Caterpillar Performance Handbook, Edition 26.

OSHA regulations(Standards -29 CFR) Part 1926 Subpart P, Standard no.

1926.652 provide guidelines that must be followed in this regard. These are presented

below in the form of a graphical flow chart.

According the OSHA flow chart presented above, some kind of trench protection

system is required whenever the trench depth exceeds 5 ft. Consequently, many large-

diameter HDPE pipe installations will require such trench support. The following section

presents some of the most commonly used trench support systems.. These include: trench

boxes, drag boxes, or wood plank and struts.

3.3.2.1 Drag Box

Fig. 3.2 shows how a drag box is utilized in construction. The method of

installation requires the trench to be cut slightly wider than the box and the drag box is

lowered into position. Subsequently, backfilling inside the drag box and excavation of

the next segment of the trench proceeds simulataneously. After the backfilling has been

completed, the drag box is pulled forward into position by a large excavator into the new

excavation.

3.3.2.2 Trench Box

Fig. 3.3 is a sketch of a trench box. It is a modular system composed of two

support walls separated by props. Fig. 3.4 demonstrates the method of installation of

31

Is the excavation more than 5 ft in depth?

Is there potential for no

Cave-in?^^

Is the excavation

^ entirely in stable

rock?

NO YES

• Excavation may be made with

Vertical sides

YES NO

^ Excavation must be sloped or shored ^

or shielded

f Sloping selected Shoring or shielding selected

Fig. 3.1 Flow Chart for Selection of a Trench Protection System

trench boxes. Contractors have generally found that three boxes are sufficient to operate

an efficient cycle of work - one box going down with excavating, a second box already

founded to provide protection for pipe installation and the third box coming up as the

backfilling proceeds.

Fig. 3.5 shows the use of slide rails in the installation of trench boxes. The trench

box system has been developed a stage ftirther to incorporate slide posts driven ahead of

the slide plates to act as guides. This method overcomes difficulties in trench box

withdrawal in granular soil.

32

STFENING PLATE P U l FROM EXCAVATOR

"Wirr

PIPE

Fig. 3.2: Drag Box Installation

Fig. 3.3: Trench Box Module

33

Fig. 3.4: Pipe Installation with Trench Boxes

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3.3.3 Earth Moving Equipment: Bulldozers, Loaders. Scrapers and Graders

The construction sites are often uneven and require leveling. When construction

takes place in such rough terrain, excavated material is removed, transported and

deposited in a cycle. There is a fairly broad range of earth moving equipment is available

and the most suitable equipment must be selected depending on specific site conditions.

The bulldozer is very versatile machine and is used frequently for stripping top soil,

clearing vegetation, pushing scrapers, spreading and grading. The bulldozer can be used

effectively for moving earth over short distances up to 100 m (300 ft ). However many

projects, necessitate a combined load, haul and discharge system at least up to a distance

of 3 km. The situation calls for a robust excavator, capable of travelling over rough

terrain to eliminate the use of trucks and wagons on public roads. The scraper has been

developed specially to cater for this medium distance haul. Essentially the earth is cut and

loaded directly into the scraper box (or bowl), transported to the discharge area and

finally spread in layers. The whole process takes place in a continuous cycle. The type of

machine to be adopted depends upon travelling distance. The loader is a machine which

serves the purpose of both the fixed-position excavator and transporter over short

distances of perhaps 10-20 m (30-60 ft).

3.3.4 Compaction Equipment

Compaction of the backfill within the trench requires special equipment because

of the limited space available between the pipe and the trench wall. Walk-behind

vibratory plate compactor and impact rammers (Fig. 3.6) are the most common and

convenient types of compactors contractors use for compaction of backfill inside a trench

for pipeline installation.

Rammers are the best type of compactor for clay and cohesive soils, where we

need to squeeze out air and excess water. The shoe or foot of rammer will come off the

ground, approximately 2 or 3 inches and then slap down about 600 to 700 times a minute

in order to really pound the soil. The vibratory compactors are well suited for granular

material. However, they do not work well in clay soil because their compacting action

36

tends to pump water to the surfece where it creates mud. The machine bogs down

because it does not have enough amplitude to separate itself from the clay.

The backfill materiiils recommended in the specification other than the flowable

backfill are course granular materials and hence, there should be no problem with using

vibratory plate compactors for compacting backfill ofHDPE pipe installation. Vibratory

compactors and vibratory plates in particular rest du-ectly on the ground. The compactor

with smallest plates dimension measure 12 inches wide by 25 inches long. A rotating

offset weight in the plate creates vibrations. These vibrations reduce the friction between

the soil or gravel particles in backfill, then allow gravity and the weight of the machine to

compact that material. There are two types of vibratory plate compactors: forward-plate

compactors and reversible-plate compactors. Reversing-plate machines are more

productive than forward-plate.

While working in a confined place with a forward plate unit such as inside a

trench, once the pipe is laid workmen have got to turn that machine around, it is hard to

do, because it is designed to go in only one direction only. Forward-plate machines use

one counterbalanced weight to produce compaction energy. A reversing plate machine

uses two. Changing the pitch on one of those weights allows the machine to go from

forward to reverse simply by pulling a lever.

3.3.5 Weight of Equipment

Once the pipe soil envelope is prepared, any of the equipment discussed above

may traverse buried pipe zone and hence affect the structural integrity of the installed

pipe. Therefore, proper cover must be provided to avoid potential damage to the pipe.

The selection of the mmimum cover required, as explained in Section 3.8 is done based

on the operating weight of the equipment. Table 3.5 that provides approximate weight of

most of the construction equipment that might traverse that pipe-soil zone. Data in this

table has been obtained from Caterpillar Performance Handbook, Edition 26.

37

Vibratory Plate Compactor

Impact Rammer

Fig. 3.6: Commonly Used Compactors

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3.4 Deficiencies in the Draft Specification

The next step in the constructibility review involved careful examination of each

sub task along with the relevant portions of the draft specification to identify potential

problems in implementation. During this process, the researchers relied heavily upon the

input they collected from the field construction personnel. This review identified a

number of deficiencies or problem areas that deserve special attention. These are as

follows:

a. Minimum trench width requirements,

b. Types of backfill material allowed,

c. Granular backfill gradation specifications,

d. Minimum cover specifications.

Each of these topics is discussed in detail in the following sections.

3.5 Minimum Trench Width Requirements

Section 6.1 of the draft specification deals with trench excavation. It specifies

that "the trench width shall be sufficient, but not greater than necessary, to allow working

room to properly and safely compact haunching and other embedment materials." Since,

in most cases, the native material does not meet the specifications for pipe backfill

suitable material has to be obtained and then transported to the jobsite at a cost.

Therefore, from a project economics standpoint, it is important to keep the trench width

to a minimum. At the same time, however, the trench should be wide enough to allow

placement and proper compaction of the backfill. The minimum trench width

requirements found in the draft specification depend on the type of backfill used. They

are as follows:

Type I Backfill Outside pipe diameter +12 inches.

Type II Backfill Outside pipe diameter x 1.25 + 12inches.

One of the issues that was addressed during this constructibility review involved

the minimum trench width specifications for installations where Type II backfill (i.e.,

granular backfill) was used. The current specification was based on the guidelines found

in ASTM D 2321: Standard Practice for Underground Installation of Thermoplastic Pipe

40

for Sewers and Other Gravity-Flow Applications. However, during the field tests

conducted in this research, it was observed that the above minimum trench width

specifications did not provide adequate room for the operation of backfill compaction

equipment. Therefore, this problem was investigated during the constructibility review.

As a first step, the minimum trench width guidelines developed and used by

various agencies were compiled. These data are shown in Table 3.6. The last column in

this table represents the trench widths calculated by the draft specification. Comparison

of these numbers reveals that there is significant variation in the minimum trench width

recommendations developed by different agencies. For large diameter pipe (i.e., 36in and

above), the AISI Handbook, NCSPA installation brochure and UniBell Handbook

provide the smallest minimum trench widths. Minimum trench widths specified in

AASHTO Bridge Design Manual Sections 12 and 26 are largest. Fig 3.7 shows a

comparison of some of the more commonly used minimum trench width guidelines.

Secondly, the overall dimensions of the more commonly used backfill compactors

were reviewed to determine, the minimum space that would be required to operate these

equipment. Based on the information reviewed it was determined that a minimum of 18

inches will be needed to operate most vibratory plate compactors or impact rammers

without disturbing the pipe. Consequently, the minimum trench widths were calculated

allowing 18in space between the pipe and the trench wall. These calculations are

summarized in Table 3.7. Based on this review, it is recommended that the minimum

trench width in the specification be modified according to Table 3.8. Comparison of the

minimum trench widths recommended in Table 3.8 and those shown in Table 3.6 reveal

that the new guidelines closely match with AASHTO Section 12 and Section 26

guidelines.

41

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44

3.6 Types of Backfill Material

Section 6.8 of the draft specifications deals with backfill materials. It allows the

following two types of backfill materials.

Type I Backfill - Flowable Backfill in accordance with Special Specification

4005.

Type II Backfill - Granular Material that meets the gradation requirements of

Type B, C, D or F aggregate mixtures m Item 334 or Item 340.

One of the key issues addressed during this constructibility review involved the

availability of the specified backfill material at economical prices in various parts of

Texas. To examine this issue, a survey was conducted among the materials or laboratory

engineers in all TxDOT districts. As a first step, a copy of the draft specification was

sent to each district lab engineer. Then they were asked to provide information on the

availability and the cost of each specified backfill material in their district. They were

also asked to identify altemative materials that are economically available within the

region that may be used as HDPE pipe backfill. The information collected from this

survey is summarized in Appendix C. Review of the information received during this

survey lead to the following important findings.

a. Cement stabilized sand is a common backfill material that is widely used by many

TxDOT districts. In some districts, such as Houston and Beaumont this material

is foimd to be more economical than conventional granular backfill. This was

confirmed by data collected during the economic analysis phase of this research.

Therefore, cement stabilized sand should be included in the specifications as an

acceptable backfill material.

b. The mix design of the Special Specification 4005 flowable backfill is designed to

provide a much higher strength than is necessary for pipe backfill purposes. This

flowable backfill is considerably more expensive than other backfill materials. A

TxDOT special task force has examined a number of different flowable backfill

specifications and identified Special Specification 4438: flowable backfill as a

more suitable backfill material for this application. Item 4438 corresponds to a

lower strength (28-day compressive strength of 80-150 psi) and therefore a more

45

economical flowable fill. Therefore, Item 4438 should be used instead of Item

4005 in the specifications for Type I backfill materials. However, concern has

been raised with respect to lack of control on the short-term strength of this

particular flowable fill. Item 4438 specifies the 28-day strength to be a minimum

of 80 psi but does not specify a minimum short-term, say 24 hr, strength. Short-

term strength of the flowable fill is of importance because, in many pipe

installation projects, the trench must be covered up and the highway opened to

traffic as soon as possible. Therefore special attention should be paid to the short-

term strength of the flowable fill when this type of backfill is used in pipe

installation projects.

3.7 Granular Backfill Gradation

Gradation of the Type II granular backfill is specified in Section 6.8 of the draft

specification. In this section it is stated that "Type II backfill consists of granular

material that meets the gradation requirements of Types B, C, D, or F aggregate mixtures

in Item 334: Hot Mix-Cold Laid Asphalt Concrete Pavements and Item 340: Hot Mix

Asphalt Concrete Pavements." Although the specified gradation bands match the HDPE

pipe backfill requirements very well, there is a major difficulty associated with the use of

this specification. In the preparation of an asphalt concrete mix of a specified type,

aggregate of different size fractions are fed into the plant in the correct proportions and

then blended inside the hot mix plant. Accordingly, aggregate blending to achieve

specific gradation requirements of Types B, C, D and F aggregate mixtures is

accomplished within the hot mix plant. Thus, achieving the same Types B, C, D and F

gradations for another application is difficult.

Item 334 and Item 340 were used in the backfill material gradation specification

with the expectation that they will make the task of finding the appropriate material easier

for the contractor. However, experience from the pilot construction projects proved that

it created more ambiguity and confusion for the contractor than it helped him identify

suitable granular backfill. Therefore, the following altemative approach is recommended

for use in the granular backfill specification. Table 3.9 below specifies the gradation

46

band for granular backfill. In addition, items from the current TxDOT Standard

Specification that may meet the specified gradation requirements are identified in a

footnote to the table.

Table 3.9 Gradation Requirements for Type III Backfill

Sieve No.

1 inch /g inch

Vi inch /g inch

No. 4 No. 10 No.200

Percent Retained (Cumulative)

0-5 0-35 0-75 0-95

35-100 50-100 90-100

3.8 Minimum Cover

One of the important aspects that must be addressed in the specification for

installation of the pipe involves the minimum cover requirements to protect the pipe from

vehicular loading. In arriving at a suitable thickness for the minimum cover, one must

consider two types of loadings; (a) loadings from off-road vehicles, such as constmction

vehicles that may traverse the pipe during constmction, (b) repeated loading from

vehicles that travel on the highway once the pipe installation is complete.

In the original version of the specification that was developed by the research

team and presented to the TxDOT project monitoring committee on April 30, 1998,

minimum cover issues were addresses in Sections 3.1 and 4.5.4. Figure 3.8 on the

following page presents the relevant sections from the above specification. During the

constmctibility review, the project monitoring committee (PMC) was asked to review the

specifications and provide their comments. Based on their review, the PMC raised a

question with respect to lack of a clear definition of "heavy constmction vehicles." This

was an important issue because the specification requires the constmction of a special

ramp to provide a minimum 1.2 m (4ft) cover before heavy constmction vehicles could

traverse the pipe. However, building of such a ramp will require the use of constmction

47

vehicles. This raises a question as to which constmction vehicles are not considered

"heavy" and therefore may be used in the constmction of the ramp.

In response to the above comment, the researchers conducted a thorough review

of the existing information on effects of heavy vehicle loading on the thermoplastic pipe

with minimum cover. The findings indicated that, in general, 300mm (1 ft) minimum

cover has generally been found to be adequate to protect the pipe from loading due to

many commonly used constmction equipment such as excavators, rollers, front-end

loaders, backhoes etc. However, larger cover is needed to protect the pipe from

constmction equipment such as earth movers, elevating scrapers and cranes. However,

since each type of constmction vehicle comes in a broad range of models, it is not

possible to categorize constmction vehicles into two classes as "light, for which 300mm

is adequate" and "heavy, for which minimum cover larger than 300mm is required."

Therefore, it is recommended that the specifications be revised in the following manner

as stated in the final specification (Appendix B, pp. 108-109).

The backfill material shall be placed evenly and simultaneously on both sides of the pipe to not less than 300 mm (1 ft) above the top of the pipe. No heavy constmction equipment with axle loads equal to or larger than 40-kips shall be permitted to traverse the pipe trench. If the passage of such heavy constmction equipment over an installed pipeline is necessary during constmction, compacted fill in the form of a ramp shall be constmcted to depth of one pipe diameter above the crown of the pipe.

The recommendations given above are based on information available in

published technical literature. In the third and final year of this research study,

appropriate field testing will be conducted to check the validity of the above specification

for the specific types of backfill material used in TxDOT pipe installation projects.

Revisions, if found to be necessary, will be incorporated in the final version of the

specification that will be delivered to TxDOT at the conclusion of the study.

48

3.1 Minimum Soil Cover

The minimum cover from the pipe crown to the top of the road subgrade or ground surface should be as specified Table 2 below.

Table 2. Minimum Soil Cover Type of Pavement Minimum Cover

inches mm Rigid Pavement Flexible Pavement Unpaved Roadway No Vehicular Loading

12 18 27 21

300 450 675 525

4.5.4 Final Rackfill - Final backfill consists of the zone that extends from 1 ft (300 mm) above the crown of the pipe to the base or final grade. Placement and compaction of the final backfill should be performed according to specifications provided in the plans. Heavy constmction vehicles should not be allowed to cross over the pipe until the compaction has been completed to the finished earthwork grade or to an elevation of at least 4 ft above the crown the pipe. If the passage of constmction equipment over an installed pipeline is necessary during constmction, compacted fill in the form of a ramp shall be constmcted to a minimum elevation of 4 ft (1.2 m) above the crown of the pipe. Any damaged pipe shall be replaced at the contractor's expense.

Fig. 3.8 Excerpts from Draft Specifications that Address Minimum Cover Requirements

49

CHAPTER 4

ECONOMIC ANALYSIS

4.1 Overview

In this chapter, HDPE pipe is compared with reinforced concrete pipe and

cormgated metal pipe in terms of material and installation costs. The chapter begins with

a general economic comparison between different pipe products. This discussion reviews

the advantages and disadvantages of using HDPE pipe in place of concrete and

cormgated metal pipe from an economic point of view. Subsequently, Section 4.2

presents a similar comparison based on data compiled by several other state DOTs on as-

installed costs for different types of pipe. Several interesting observations can be made

from this data analysis and review. First of all, review of data indicates that the

acceptance ofHDPE pipe as a viable altemative has resulted in lower unit bid prices for

all pipe products. Secondly, the available data shows that as-installed costs for HDPE

pipe have been lower than for other pipe products. A detailed review is found in Section

4.2. Section 4.3 presents a comparison on as-installed cost ofHDPE pipe and RCP based

on an analysis performed for some example-pipe-installation projects using a software

named 'PipePac 2000'.

The two main material resources required in large diameter pipe installation are

pipe and trench backfill material. The unit prices for both of these, especially backfill

material, depend largely on the project location. Therefore, the economic analysis

conducted in this study also involved a study of how these parameters vary within the

state. Accordingly, data on backfill material prices were collected from different TxDOT

districts and reviewed. Section 4.3 of this chapter presents the results from the above

data review and analysis.

The last section of this chapter. Section 4.4, presents the findings from a

parametric study. This parametric study is based on a detailed analysis that was

conducted to obtain estimates of as-installed costs for a hypothetical pipe installation

project when pipe installation is performed according to TxDOT specifications. It

examines the influence of pipe material (HDPE vs. RCP), pipe diameter and backfill

material price on overall project cost by varying each parameter within the complete

50

range of values found within Texas. Several useful conclusions were drawn based on the

findings from the above parametric study.

Concrete pipe has thicker pipe wall and is much heavier than its HDPE

counterpart that meets the same stmctural requirements. The heavier weight of concrete

pipe results in higher transportation cost per mile. In other words, a tmck with given

weight carrying capacity can transport a much larger quantity (i.e., total pipe length) of

HDPE pipe than concrete pipe. Because of its light weight and ease of handling, HDPE

pipe can be easily nested and stacked up higher on the tmck allowing a larger quantity of

HDPE pipe to be transported in a single trip. However, it is important to note that this

advantage is somewhat ofi&et by the longer distances that HDPE pipe must be transported

in comparison to conventional RCP pipe. There are fewer number ofHDPE pipe

manufacturing plants when compared with RCP pipe manufacturing plants. For example,

there are only two HDPE pipe manufacturing plants within the entire state of Texas: ADS

pipe manufecturing plant in Enis (near Dallas) and Hancor pipe manufacturing plant in

Yoakum. In comparison, there are more than seven RCP manufacturers within Texas as

listed in Highway Dope Book and& Directory (Whitley & Siddons, Dec. 1998). Some of

those RCP manufacturers have more than one production plants located in different

districts within Texas. Therefore, the average distance from the point of production to

the project site is larger in the case ofHDPE pipe than it is for RCP. A more detailed

discussion of pipe prices can be found later in a subsequent section of this chapter.

In addition to possible savings in transportation costs, the lighter weight of the

HDPE pipe also results in savings in labor cost during installation. Due to the light

weight ofHDPE pipe, less labor is required in its handling and placement. In addition,

because of the lighter weight ofHDPE pipe, they come in longer pipe lengths. The

typical length ofHDPE pipe (also called "stick length") is 20ft whereas the typical length

of RCP is in the range of 8-10ft. Accordingly, HDPE pipe installation involves fewer

joints. This results in significant savings in overall project time and therefore, project

cost. In addition, pipe joints are also the most critical places of the drainage system from

the view point of maintenance. Therefore, it can be anticipated, that fewer joints in

HDPE pipe will lead to lower makitenance costs. The manufacturers of smooth-lined

51

polyethylene pipe (SLPE) also make the claim that SLPE has better hydraulic flow

characteristics than concrete pipe and thus lowering maintenance costs. However,

American Concrete Pipe Association (ACPA) refutes the above claim based on research

conducted by Utah State University (ACPA Concrete Pipe Insights, 1997). ACPA

suggests that an extrapolation of the test values (only 12" through 18" HDPE pipes were

tested) results in laboratory values as high as 0.015 for 24" diameter and 0.019 for 36"

diameter SLPE. These numbers are higher than design Manning's n value of 0.012 and

0.013 that is generally recommended by the concrete pipe industry for RCP. Therefore,

at this point it is not clear whether the smooth lined HDPE pipe does have superior

hydraulic flow characteristics than other pipe products or not.

HDPE pipe, being a more flexible product than reinforced concrete pipe, depends

more on the surrounding backfill material for stmctural support. Therefore, quality

control during the placement and compaction of baickfiU is a very important aspect of

HDPE pipe installation. For this reason, specifications for installation tend to be stricter

for HDPE pipe than those for rigid pipe systems such as RCP. These specifications

typically include requirements for special backfill materials, special precautions during

handling and placement of the pipe, special precautions to avoid potential problems due

to pipe floatation, requirements on larger minimum covers to prevent pipe damage,

requirements to measure pipe deflection to ensure satisfactory installation etc. Such

requirements tend to drive the cost ofHDPE pipe installation higher. Another drawback

that is often cited by highway agencies with regard to the use ofHDPE pipe on a routine

basis is that they are not adequately staffed to provide close supervision that is needed in

such installations. As a result, their HDPE pipe installation specifications tend to be

overly conservative. Unfortunately, when such conservative practices are used, any

economic benefit that could be gained from the use ofHDPE pipe will be lost.

52

4.2 Review of Information from Other States

4.2.1 Introduction

Section 4.1 presented a general comparison between HDPE pipe and reinforced

concrete pipe from an economic point of view. Apart from this general overview, effort

was also made to collect and review data on actual as-installed costs for HDPE pipe from

various agencies that have used this product in highway drainage applications. This

section summarizes the findings from the above review. The review primarily focuses on

two separate issues; (a) the impact of accepting HDPE pipe as a biddable altemative for

large-diameter pipe installations on the unit bid prices for other pipe products, (b)

comparison between the as-installed cost for HDPE versus that for reinforced concrete

pipe. However, as the reader reviews the information presented below, it is important

that he (or she) keeps the following points in mind.

a. The installation costs for a given pipe product depends on the specifications

used in its installation. These specifications may vary significantly from one

agency to another. Stringer requirements will obviously cause the installation

costs to go up. Therefore, the numbers reported for one agency or location may

not apply to another. Additionally local conditions such as availability of

quality granular backfill also play an important role in determining which pipe

product is most economical and what margin of economical benefit it will yield

over other products.

b. This research focuses on large-diameter (36in or larger) pipe category.

Therefore, this economic comparison should strictly be confined to large

diameter pipes only. Unfortunately, the available data did not always categorize

percent savings on installation costs by different pipe diameters. Inevitably,

some loss in accuracy in data analysis occur when data from different pipe

diameters are pooled together.

The authors made every effort to perform an unbiased review. It must be

pointed out that, nearly all of the data that surfaced during their search came from

databases that were compiled by thermoplastic pipe manufacturing industry.

53

Nevertheless, these data were originally obtained from independent agencies such as state

DOTs and City Public Works Departments.

4.2.2 Economic Impact from the Acceptance ofHDPE as a Biddable Altemative

This section deals with the overall impact from introducing HDPE in the bid

process for pipe installation projects for all types of pipe. It includes a review of

available data on actual bid prices for as-installed costs for different pipe products when

HDPE pipe is allowed as a biddable altemative versus when HDPE pipe is not allowed as

a biddable altemative. The above review indicates that the competition created by

including HDPE in the bidding process leads to significant benefit to the transportation

agencies. This benefit is two-fold and is discussed in the following sections.

First of all, the unit bid price for RCP as-installed cost becomes lower when

HDPE is allowed to bid compared to the case where HDPE is not allowed in the bidding

process. Limited data presented in Table 4.1 supports this statement. This table has

been compiled from the South Carolina State DOT Bid Tabulation (Jan 1996 - Feb

1997). Savings on 18in and 24in RCP bid price were found to be 7.6% and 10.4%

respectively as it appears in this table. Unfortunately, similar data was not available for

pipe with larger diameters where bid prices for RCP pipe could be con^ared for the two

bidding environments, i.e., when HDPE was present as a biddable altemative and when

such altemative was not present.

A second and a more significant benefit resulting from the presence ofHDPE in

the bidding process is that it lowers the overall bid price for the as-installed cost for the

pipe installation project.. A con^arative study on available data on average unit bid

prices for installations with different pipe products suggests that unit bid price for HDPE

is the minimum among different pipe products. Therefore, the overall as-installed cost

would be based on HDPE pipe which, according to the data, yielded

54

Table 4.1: Impact on Average Unit Bid Price of RCP when HDPE Pipe was Permitted to Bid as Experienced by SCDOT, 1996-1997

Pipe Diameter

18in

24in

Average Unit Bid Price of As Installed Cost When

RCP is the only Pipe Material ($/ft)

$17.59

$23.7

4

Average RCP Unit Bid Saving on RCP Price of As Installed Cost When HDPE When HDPE was Present was Allowed an

as Altemate ($/ft) Altemate ($/ft)

$16.27

$21.30

7.6%

10.4%

significant savings over RCP as installed cost. Table 4.2 summarizes the available data

on unit bid prices for pipe installations when HDPE was available as a biddable

altemative. Majority of the data shown in Table 4.2 is limited to HDPE and RCP.

However, in some instances, they include bid prices for other pipe products such as CMP

as well. Pipe diameter tabulated in Table 4.2 ranges from 18in through 42in. Only Iowa

State DOT has the experience with bidding and using 42in pipe and no data is available

for 48in diameter pipe. Accordingly, these pipe installations have been completed during

the time period from 1989 through 1999 and all available data have been tabulated in

chronological order. In Table 4.2, it is noticed that as-installed cost for HDPE pipe of

same diameter varied significantly from once state DOT to another. For example, for

36" diameter HDPE pipe as-installed costs were $45.84, $26.38, $39.03 and $42.39 as

experienced by NYSDOT, ODOT, OKDOT and SCDOT, respectively, in the time range

from 1991 through 1997. Ohio DOT's as installed cost is noticeably lower than any other

state DOTs'. The use of different specifications by different agencies and local

conditions such as availability of specified backfill material may explain the observed

cost variation from one state DOT to another. Additionally, all of the reported data do

not correspond to the same time period. This makes direct comparison difficult owing to

rising labor and material costs. Interestingly however, review of data from NYDOT for

which data was available for both 1991-92 and 1998-99, shows that the as-installed cost

55

has remained neariy the same over the 7 year period. In fact, the as-installed cost for

36in diameter pipe has come down. Subsequently, Table 4.3 which presents the same

information in summary form shows the fact that percent savings reported by different

state transportation agencies varied widely. Maximum savings due to low bid price of

HDPE pipe is as high as 61% relative to RCP bid price. The minimum savings relative to

RCP was 16.% for bidding on 30in diameter pipe as experienced by NY State DOT when

HDPE pipe was bid on an equal basis along with RCP and CMP.

Also it is of interest to note that percent savings for comparatively smaller

diameter pipe such as 18in, 24in were similar to those for HDPE pipe of diameter as high

as 30in, 36in and 42in. Thus, the state DOT data reported above lead to the conclusion

that HDPE pipe is more economical than RCP pipe for both smaller diameter and large

diameter pipe. In addition to this comparative review on unit bid price of as-installed

cost ofHDPE and other pipes, the history of using HDPE along with RCP and CMP by

NY State DOT in the past few years support the same view. This data is presented in Fig.

4.1. This figure has been derived from data published in Cormgated Polyethylene Pipe

Association (designated as CPPA) Press Release, dated April 7, 1997. The original

source of these data was NYSDOT Material Bureau. NYSDOT began using large

diameter HDPE pipe in 1989. Fig. 4.1 shows that even though the total use ofHDPE was

just 1% in 1989, the percentage ofHDPE pipe use in the following years gradually

increased. As a continuation of this fact cormgated HDPE pipe accounted for 48 percent

of all large-diameter pipe used in 1996 roadway drainage projects. Fig. 4.1 speaks for

itself and it depicts the fact of increasing popularity ofHDPE in the state projects and the

reason is obviously the savings in installation costs for making HDPE as their material of

choice in place of RCP or CMP.

56

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Table 4.3: Percent Savings due to Presence ofHDPE in the Bidding Process

Pipe Diameter

I Sin

24in

30in

36in

42in

48in

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4.3 Comparison ofHDPE and RCP As-installed Cost Based on Analysis Performed with TipePac 2000'

In addition to the comparison made in the previous section based on the actual

bid prices, an analysis was performed using Cost Analysis of Pipe Envelope (referred to

as CAPE) of the software PipePac 2000. American Concrete Pipe Association has the

copyright for this software. 'PipePac 2000' allows calculation of as-installed costs for

both RCP and HDPE pipe. Any analysis performed using this software represents

economic perspective of concrete pipe industry about various pipe products.

This section summarizes the results from the analysis performed for several

example-projects ofHDPE and RC pipe-installation in order to get the comparative

picture on which pipe product is economical. The main parameters requiring input for

the analysis are pipe price, pipe diameter, hauling and tippmg rate and granular backfill

price. Trench dimensions such as trench width, bedding depth, excavation height receive

default values once a diameter is selected for an analysis. As-installed cost ofHDPE and

RC pipe estimated using this software is listed in Table 4.4. RCP Installation type Class

C is listed which assumes the use of native soil for backfilling. RCP price considered in

this analysis is the minimum listed pipe price of Hanson Concrete Products. Whereas

HDPE pipe price is typical price for Texas region listed by Advanced Drainage System,

Inc. Savings from using HDPE pipe were calculated accordingly. Table 4.4 shows that

approximately 7% to 9% savings on using HDPE pipe is possible over RCP.

59

It must be noted that there are a number of significant limitations in the PipePac

2000 analysis. The software estimates the total pipe installation cost as the sum of cost

of the pipe, cost of backfill material and cost of removal and disposal of excavated native

soil. It does not consider cost of labor and equipment for the installation. Therefore, it

does not appropriately consider reduction in cost due to less labor and faster installation

ofHDPE pipe resulting from the lighter weight and longer joint spacing for this type of

pipe.

4.4 Economics: State of Texas

4.4.1 Introduction

Data presented and discussed in the preceding section clearly indicate that there is

significant economic incentive for transportation agencies to include HDPE pipe in the

bidding process for pipe installation projects. At the same time, however, it is important

to point out that the pipe installation costs vary with the installation specifications used

by each agency. The pipe installation costs also vary from one location to another

depending on local conditions such as availability of specific types of backfill materials.

Also, the analysis performed with PipePac 2000 does not consider some of the important

factors that affect the total installation cost ofHDPE pipe and RCP. Therefore, before

any conclusions could be reached concerning the potential savings to be gained by

TxDOT from the use ofHDPE pipe, it is necessary to perform a closer review of the

specific conditions that exist within Texas. Consequently, a survey was performed to

determine the pipe prices and backfill material prices within various parts of Texas.

Among all the parameters that influence the overall pipe installation cost, these two, viz.

pipe price and the backfill material price are most liable to vary from one region to

another. The findings are summarized in the following two sections 4.3.2 Pipe Price and

4.3.3 Backfill Material Price. Subsequently, in Section 4.4 this information is used in a

detailed economic analysis to determine cost of pipe installation according to draft

specifications developed in this research.

60

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62

4.4.2 Pipe Price

In order to have the most recent pipe price information in different parts of Texas,

the two largest HDPE pipe manufacturers in Texas and two concrete pipe manufacturers

were contacted. Each of these companies was asked to provide price quotations for their

products. Table 4.5 lists price of smooth interior cormgated HDPE pipe for pipe

diameters ranging from 18in to 48in. The listed prices include the price of pipe, joints

and freight cost. Manufacturer 1 recommend that if delivery is requested earlier than 5

days, extra freight cost will be added. For overnight delivery, an extra $200+$ 1.67 per

mile is required. The prices listed for manufacturer 2 could be considered delivered

prices anywhere within Texas, provided the order was in full tmck load quantities. If the

order was less than tmck load amounts, a freight charge could be applied. This amount

would be no more than $150.

Table 4.5: Typical Smooth Interior Wall Cormgated HDPE Pipe Pricing (May 12, 1999)

Diameter Length Price/ft^$) Price/ff($) Manufacturer 1 Manufacturer 2

18" 24" 30" 36" 42" 48"

20' 20' 20' 20' 19.5' 19.5'

6.30 9.71 15.97 19.43 30.45 36.71

5.95 9.44 16.65 20.00 27.00 34.00

Similariy, prices per ft of ASTM C-76 Class III (Tongue and Groove Joint)

reinforced concrete pipe from the two RCP companies are shown in Tables 4.6, 4.7 and

4.8. Table 4.6 shows the price quotations provided by the first RCP manufacturer in the

vicinity of San Antonio while Table 4.7 shows the RCP pipe prices for Dallas Fort Worth

and vicinity. Table 4.8 are price quotations obtained by a second RCP manufacturer, also

for Dallas Fort Worth metropolitan area and its vicinity. These figures include the price

of the joints.

63

One significant difference that can be observed between the price tabulations for

HDPE pipe and RCP is that RCP prices vary with the distance between the

manufecturing plant and the project location whereas HDPE prices do not. This

difference is due to the significant costs associated with the transportation of RCP. This

is an interesting observation because, in comparison to RCP, the HDPE pipe

manufecturing plants are few and far between. For example, each of the two concrete

pipe suppliers mentioned above, has six RCP manufacturing plants in different parts of

Texas. The HDPE pipe manufacturer, on the other hand, has only one manufacturing

plant in Texas that serves the whole state and some of the neighboring states as well.

Nationwide, they have 33 storage locations and 4000 independent distributors.

Nevertheless, the average distance from the point of production ofHDPE pipe to point of

pipe mstallation is much larger than for RCP pipe. The information presented in Tables

4.6, 4.7 and 4.8 shows that despite longer transportation distance, HDPE pipe price is

lower than concrete pipe. The probable reason for this is the difference in cost of raw

materials used in the production of the two different types of pipe.

It was also reported that price of RCP varies with the quantity ordered. In other

words, contractors receive discounts when they order large quantities. Based on the

information received from RCP manufacturers, these discounts may be as high as 20%.

According to information presented in Table 4.6, the minimum listed price for RCP

corresponds to RCP pipe produced at San Antonio plant and delivered within Zone I.

Accordingly, the least possible price of RCP could be calculated by applying 20%

discount to that minimum RCP price. Figure 4.2 presents a con^arison ofHDPE pipe

price against RCP pipe prices for pipe diameters ranging from 18in to 48m. In this

comparison the HDPE prices from both the manufacturers were used. Because RCP

prices varied from one delivery zone to another, the maximum price, the minimum price

and minimum price with 15% discount are plotted. It shows that HDPE pipe price listed

by each of the two manufacturers is lower than RCP pipe price even when a high

discount rate of 15% is applied.

64

4.4.3 Backfill Material Price

4.4.3.1 Overview

Backfill material is one of the most important among all the factors that control

the as-uistalled cost of the HDPE pipe installation. The new backfill material

specifications have been developed so that satisfactory pipe performance can be ensured

with reasonable level of quality control during backfill placement and compaction.

Most native soils will not meet these specifications and therefore, suitable backfill

materials must be obtained from outside sources and transported to the site. Thus, the

specified backfill material comes at a cost and it is an important element that must be

considered in the estimation of the as-installed cost of the pipe. The availability of a

given type of backfill material and its price vary significantly from one location to

another. Therefore, as part of this economic analysis, information on availability and

price of each type of specified backfill material types within different regions of the state

was collected and reviewed. The findings from the above review is presented in this

section of the report.

Section 4.3.3.2 below begins with a detailed description of the data collection

procedure. It also presents all the data collected in tabular form. Subsequently, it

presents the findings from the data review and analysis. The data review was performed

with the following specific objectives in mind. First of all, the prices of different types of

backfill material allowed in the specifications are reviewed to establish the general price

range for each. Secondly, the price quotations obtained from different regions are

examined to determine whether they show any trends or patterns with respect to

geographical location. Finally, the findmgs from this review are used to detemme the

overall as-installed cost of the pipe with each type backfill material allowed by the

current specifications. These as-installed costs are also compared with as-installed costs

of RCP pipes of same diameter.

65

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4.4.3.2 Data Collection

The first step in the review process involved the collection of data on current

backfill material prices in various parts of Texas. This was accomplished in two

different ways:

a. Contacting laboratory engineers in TxDOT districts and collecting their input on

prices of suitable types of backfill materials that are economically available in

each district.

b. Extracting data from TxDOT's website that publishes 12-month average unit bid

prices based on construction projects that have been completed in each district.

Backfill price data obtained from district lab engineers in all 25 TxDOT districts

are listed in Appendix C. Table 4.10 is an excerpt from Appendix C that lists some of the

more economical materials available in various parts of Texas. Similarly, data collected

from average bid price tabulations published in TxDOT's website are summarized in

Tables 4.11, 4.12, and 4.14. They represent the average unit bid prices compiled from

numerous projects during the year, 1999. Table 4.13 shows unit bid prices for cement

stabilized backfill (also referred to as Type II backfill in the specification for thermo

plastic pipe), whereas Table 4.14 summarizes the bid prices for flex base materials.

However, not all the data that were collected in this manner could be directly

used in fiirther analysis. First of all, it could be easily seen that unit bid prices for

backfill material were quite sensitive to the quantity of material supplied. In general, the

unit price decreases as the quantity supplied increases. As a result, unit price applicable

to one project may not be directly compared with unit price for another unless the

quantities of backfill material supplied in the two cases are similar. Another factor that

makes direct comparison of backfill material difficult involves the form in which backfill

prices are reported. For example, in Table 4.14, unit bid prices of flexible base material

are tabulated in two forms: 'roadway delivery' price and 'complete in place' price.

Roadway delivery price refers to the price of flexible base material delivered at the job

site and thus, it includes the cost of transportation of the material. On the other hand,

price of flex base in 'complete in place condition' includes cost of material, cost of

transportation and cost of placing of placing the material and compacfing it to specified

69

density. Additionally, because of the volume reduction associated with compaction of

the material, it will be incorrect to compare the 'roadway delivery" price with 'complete

in place' when these prices are reported in $/CY. An even greater difficulty arises with

unit prices of coarse aggregate material used in bituminous mkes. The prices quoted by

most laboratory engineers represented the price of the bituminous mix that included both

aggregate and asphalt binder. Many times these prices represented the price of the

bituminous mk in 'complete in place' condition. Because of these ambiguities, the

bituminous coarse aggregate prices were not included in any fiirther review or analysis.

Among all the backfill materials prices, flowable fill (i.e.. Backfill Material Type

I in the specifications) were the highest. Table 4.11 shows flowable backfill prices for

several districts of Texas. The unit price of flowable fill varied in the range from $53/CY

to $130/CY. However, it must be noted that although the unit price of flowable fill is

higher than that for any other backfill material type, it does not necessarily mean that

flowable backfill will result in higher as-installed cost. First, the specifications allow the

use of a smaller trench width when flowable fill is used. Therefore, the volume of

flowable fill required in a given installation is less than the volume of any other backfill

material type. Secondly, this type of backfill does not require any compaction thus

allows faster installation. These factors may partly offset the higher cost of backfill

material.

70

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71

Table 4.11 : Overall Average Bid Price of Flowable Fill in Texas Districts in 1999

District

Austin San Antonio Beaumont Wichita Falls Corpus Christie Childress Bryan Pharr Fort Worth

Item Number

4156 4156 4158 4438 4438 4438 4438 4438 4438

Qtiantity

3475 840 381 10 5 157 8 237 47

Overall Unit Bid Price of Flowable BackfiU($/CY)

53.47 55.85 68.85 75.00 100.00 120.00 125.00 127.00 130.00

Review of unit price tabulations found on TxDOT website reveals that cement

stabilized materied, i.e.. Type II Backfill in the specifications, is more widely used in

TxDOT construction projects than flowable backfill. Table 4.12 shows the cement

stabilized backfill prices for 24 TxDOT districts. The last column in the table shows the

weighted average price calculated for each district. Conqjarison of these unit prices show

that the price of cement stabilized backfiJl vary significantly. Most of the data lie in the

range between $26/CY and $87/CY although there are a few data points can be found

outside this range. Secondly, it can be observed that the prices of cement stabilized

backfill show a clear price trend according to different geographical location. Table 4.13

categorizes the cement stabilized backfill price into three different ranges; low (less than

$40/CY), medium (between $40/CY and $70/CY) and high (greater than $70/CY).

Subsequently, based on the weighted average price calculated for each TxDOT distrk t,

they are divided into different price zones. These different price zones are depicted in

Fig. 4.3. It shows that the price of cement stabilized is lower near the gulf coast. The

prices show a general increasing trend as you move away from the gulf coast with some

of the West Texas and northern districts showing the highest prices.

The third type of backfill allowed in the specifications is granular backfill. In

most regions, granular backfill is found to be the most economical option among the

three types of backfill materials specified. Once again, review of granular backfill

72

material prices was performed based on input received from district laboratory engineers

as well as unit bid price tabulation available on TxDOT website. Table 4.10 provides a

summary of information collected from district lab engineers. Review of these data

shows that the unit price of granular backfill range from about $9.50/CY to about

$25.00/CY. The next step involved review of information available on TxDOT unit bid

price tabulations. Although, granular material with gradations similar to those specified

is used in many applications including Hot Mix Asphalt Concrete, Surface Treatment,

Portland Cement Concrete, the unit prices for these items cannot be used in this review

because they do not represent cost of aggregate material alone. The only exception was

Item 247: Flexible Base. Therefore, overall average bid prices for flex base in 'roadway

delivery condition' were obtained for 15 TxDOT districts. They are listed in Table 4.14. •

The typical price range appears to be between $7.00/CY and $25.00/CY. It is

worthwhile noting that unit prices reported for 11 out of 15 districts are less than $15/CY.

At the same time, however, it must be pointed out that not all flexible base materials may

qualify for use as backfill imder the proposed specifications because of higher fines

(minus 200) content. Table 4.14 also hsts overall bid prices of flex base as 'complete in

place' condition for all 25 district which varies in the range of $14.51-$35.51. Data

presented in Table 4.14 indicate that flex base is an economically available backfill

material at an average price in almost every district of Texas. Based on the above review,

$10.00/CY was selected as a typical price for granular backfill at the low end while

$15.00/CY was selected as a representative figure for medium price granular backfill.

Based on the above review, the unit prices listed in Table 4.15 were selected as

representative figures for each backfill material category. These unit prices are

subsequently used in the estimation of as-installed costs ofHDPE pipe. This analysis

presented in Section 4.5 below.

73

Table 4.12: Overall Average Bid Price of Cement Stabilized Backfill in Texas Districts in 1999

District

Abilene (ABL)

Atlanta (ATL)

Austin (AUS)

Beaumont (BMT)

Brownwood (BWD)

Bryan (BRY)

ChHdress (CHS)

Corpus Christie (CRP)

Dallas (DAL)

ElPaso(ELP)

Fort Worth (FTW)

Houston (HOU)

Laredo (LRD)

Lubbock (LBB)

Lufldn(LFK)

Odessa (ODA)

Quantity (CY;

45.26

215.70 1,538.00

248.00

752.56 30213.00

78.20

3,018.00 581.00

583.12

47.12 1293.5

42.00 11.40

861.00

256.00 5,724.00

16.10

31,052.73 51,292.34 5,600.66

77,770.00

1,086.84 537.78

745.90 1786.96

722.50 892.6

842.65 1056.40

Average Bid Price ($/CY)

87.00

95.27 62.74

36.23

40.60 25,56

28.00

66.20 69.45

81.88

85.00 30.10

60.00 60.00 68.28

75.30 84.63

128.00

27.94 27.65 10.75 35.21

58.10 54.34

78.47 63.00

68.56 43.40

67.35 82.43

Weighted Average Bid Price ($/CY)

87.00

66.70

36.23

25.92

28.00

66.71

81.88

32.00

67.80

84.23

128.00

26.12

56.85

67.57

54.65

75.73

74

Table 4.12 (Continued)

District

Paris (PAR)

Pharr (PHR)

San Angelo (SJT)

San Antonio (SAT)

Tyler (TYL)

Waco (WAC)

Wichita Falls (WFS)

Yoakum (YKM)

Quantity (CY;

298.20 718.50

1,935.00 3,767.40

936.26 278.76

1,272.53 234.90 512.00

48.40 100.00

301.00 610.30

51.00

3,412.30 2886.00

Average Bid Price ($/CY)

132.6 87.00

62.54 37.67

36.74 83.33

71.53 67.20 68.00

120.00 141.00

61.34 45.18

79.50

39.73 33.87

Weighted Average Bid Price ($/CY)

109.7

46.00

47.43

70.13

134.00

50.51

79.50

36.65

Table 4.13: Different Price Category of Cement Stabilized Backfill in Different Parts of Texas

Districts

AUS, BMT, BWD, CRP, HOU, YKM

PHR, SJT, WAC, LFK, LRD, ATL, BRY, DAL, LBB, SAT

ABL, AML, CHS, ELP, FTW, ODA, PAR, TYL, WFS

Overall Unit Bid Price of Cement Stabilized BackfiU ($/CY)

Below $40 per CY

Between $40 and $70 per CY

Above $70 per CY

Price Level

Low

Mediu m

High

75

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76

Table 4.14: Overall Average Bid Price of Flex Base

Districts

Abilene (ABL) Amarillo (AMA) Atlanta (ATL) Austin (AUS) Beaumont (BMT) Brownwood (BWD) Bryan (BRY) Childress (CHS) Corpus Christie (CRP) Dallas (DAL) El Paso (ELP) Fort Worth (FTW) Houston (HOU) Laredo (LRD) Lubbock (LBB) Lufldn(LFK) Odessa (ODA) Paris (PAR) Pharr (PHR) San Angelo (SJT) San Antonio (SAT) Tyler (TYL) Waco (WAC) Wichita Falls (WFS) Yoakum (YKM)

1 ^ 1 ^

Overall Average Bid Price ($/CY), Roadway Delivery

-

11.74 -

-

-

15.57' -

19.31 12.41

-

-

24.60 -

13.00' -

7.00 6.27'

-

12.51 7.14

43.47' 7.10' 2.51

28.351 12.82

Overall Average Bid Price ($/CY), Complete in Place

20.53 29.20 16.67 20.64 35.51 16.59 27.88 22.68 31.96

33.30 20.51 24.87 31.04 14.51 23.81 32.24 21.00 26.60 29.96 19.18 17.15 31.23 16.94 25.54 24.7

77

Table 4.15: Suitable Backfill Materials Selected for HDPE Pipe As-installed Cost Estimation

Suitable Backfill Material Price {S/CY)

Flowable Backfill (Type I Backfill as specified in revised specificafion), 70.00 typical price in Texas region, source: Appendix C

Cement Stabilized Backfill (Type II Backfill as specified in revised 32.00 specification), low price zone, source: Table 4.12

Cement Stabilized Backfill (Type II Backfill as specified in revised 60.00 specification), medium price zone, source: Table 4.12

Flex Base, (typical price), source: Table 4.14 18.00

Granular Backfill Conforming Type III Backfill as specified in revised 10.00 specification, source: Table 4.10

Granular Backfill Conforming Type III Backfill as specified in revised 15.00 specification, source: Table 4.10

4.5 As-Installed Costs for HDPE and Concrete Pipe

Section 4.2 of this chapter presented a comparison between as-installed costs of

HDPE pipe versus concrete pipe based on data available from other states. These data

generally indicated that HDPE pipe provides savings of 20-40% over RCP. However,

because of the differences in specifications used by different agencies and availability

and prices of backfill materials, the percent savings reported by other state DOTs do not

necessarily apply to Texas. Yet again. Section 4.3 revealed the fact that savings of 7% -

9% on as-installed cost can be achieved from using HDPE pipe over RCP according to an

analysis performed with 'PipePac 2000' which is a software used by concrete pipe

industry. However, 'PipePac 2000' does not perform an analysis with all the details of

construction processes required for a high quality installation ofHDPE pipe following the

final specification (Appendix B). It does not consider cost of labor which is not same for

installation with light-weight HDPE pipe and heavy-weight RCP. Therefore, an

economic analysis was conducted in this study to estimate the as-installed costs for both

HDPE pipe and RCP. This analysis was performed for a hypothetical pipe installation

project where the pipe diameter, pipe price and backfill material price were varied within

78

typical ranges as established through previous analysis. The findings from this analysis is

presented graphically so that comparisons can be made between installation costs for

HDPE and RCP for a variety of pipe diameter, pipe price, backfill price combinations.

Section 4.5.1 presents details with regard to sources of data used and assumptions made

during analysis

4.5.1 Sources of Data and Assumptions Made for Model Project Analysis

A detailed work breakdown structure for the entire pipe installation process was

developed in Chapter 3 as the part of the constructibility review. This work breakdown

structure is presented in Table 3.2. Table 3.2 lists sub-tasks associated with different

stages of construction as well as resources (i.e., manpower, equipment and materials)

needed for the completion of each sub-task. In this cost analysis the above work

breakdown structure was further expanded to include the costs associated with each

construction activity. This enhanced work break down structure for installation ofHDPE

pipe is given in thesis as Appendix D. This new itemization forms the primary basis for

the economic analysis presented here.

The analysis in this section calculates approximate as-installed cost ofHDPE pipe

and concrete pipe installation of 18 in., 24 in., 30 in., 36 in., 42 in. and 48 in diameter for

identical utility. The whole analysis is done in one MS Excel Spread Sheet which has

been attached as Appendix E. The sources of relevant resource price information for this

analysis are as follows.

a. Information on equipment rental price, equipment capacity, equipment

size, workers wage and installation cost per unit for each sub-task is available

in Table D.l of Appendix D. Appendix D was compiled following

National Construction Estimator edited by Killey and AUyn (1997) and

Means Heavy Construction Cost Data (1998).

b. Backfill material price of six categories has been used from Table 4.15 that was

selected after a thorough review on all available backfill price data presented in

section 4.4.2.

79

c. From Table 4.5, HDPE pipe price of manufecturer l(Advanced Drainage

Systems, Inc.) was used for estimating as-installed cost. Among the prices of

RCP listed in Table 4.6, 4.7 and 4.8, RCP unit prices of the foUowing categories

have been selected to be used in this estimating:

(a) Minimum RCP price. Zone 1 of CSR Hydro-conduit, with 15%

discount

(b) Minimum RCP price. Zone 1 of CSR Hydro-conduit without discount.

(c) Minimum RCP price(FOB), priced by Hanson Concrete Products.

(d) Minimum RCP price, Hanson Concrete Products with 15% discount.

(e) Maximum RCP price, priced by Hanson Concrete Product.

(f) Discounted RCP price of Zone2, CSR Hydro Conduit.

(g) Discounted RCP price of Col. 3, Table 4.8, Hanson Concrete Products,

(h) Discounted RCP price of Col. 4, Table 4.8, Hanson Concrete Products,

(i) Discounted RCP price of Col. 6, Table 4.8, Hanson Concrete Products.

The estimation documented as Appendix E is based on some assumptions. It was

assumed that the route was perfectly flat terrain and the trench depth required was

minimum. This means that the crown of the pipe laid down in the trench remained

exactly at one pipe diameter depth according to the revised recommendation made in

section 3.8 in Chapter 3. The lengths of the pipe lines were adjusted as 170 m, 140 m,

140 m, 240 m, 220 m, 200 m for 18 in., 24 in., 30 in., 36 in., 42 in. and 48 in. diameter

HDPE pipe respectively in order to get project duration as whole number of days. For

the same reason the lengths of the pipe lines were adjusted as 90 m, 90 m, 65 m, 120 m,

110 m, 110 m for 18 in., 24 in., 30 in., 36 in., 42 in. and 48 in. diameter RCP

respectively. The project duration was rounded up in each case. For concrete pipe

excavated native soil was considered for backfilling. For HDPE pipe backfill material of

sk suitable categories presented in Table 4.15 were considered. Nine different concrete

pipe prices, mentioned previously, were used due to the distance of sites from the

manu&cturing plants. For 18 in., 24 in. and 30 in diameter pipe two temping rammers

with 10 in. plate width have been used. And for 36 in., 42 in., and 48 in. diameter pipe

two vibratory plate compactors with 12 in. plate width have been used. Two large

80

capacity backhoes will be rented. Backhoel will be doing the whole excavation job.

Backhoe2 is the larger of the two backhoes and it will perform three tasks: backfilling,

installing trench boxes and laying pipe in the trench. The total busy hrs of Backhoe2 will

determine the project duration and Backhoel will do some other subtasks like putting the

extra excavated material in the hauling truck during its idle time.

Keeping the above scenario in mind MS Excel Spread Sheet was chosen as a

convenient environment to perform this estimation by varying most significant

parameters in all possible ways. The following section performs a graphical comparison

between HDPE and RCP using the findings from the estimates presented in Appendix E

4.5.2 A Comparative Review on Findings of Model Project Estimation for Competing HDPE and RCP

The resource parameter that mainly affects as-installed cost ofHDPE pipe is

backfill material price of varying category which was discussed in Section 4.4.3. On the

other hand, varying RCP price for different supply zones appeared to be the main

resource parameter for estimating as-installed cost of RCP. Estimated as-installed cost of

HDPE pipe and RCP listed in Appendix E is summarized in Table 4.16 for relevant

resource price conditions in the districts of Texas. Prior to comparing HDPE and RCP

as-installed cost, gradients of as-installed cost of RCP with respect to six pipe diameter

categories have been plotted in Fig. 4.4. This plot also gives an idea in what range as-

installed cost of RCP can vary when pipe can be procured to the site at discounted

minimum unit price or pipe needs to be procured from a remote production plant at the

maximum unit price of RCP.

Figures 4.5, 4.6, and 4.7 immediately compares as-installed cost ofHDPE pipe

with as-installed cost of RCP for all the six pipe-diameter category on the basis of

gradually declining level of RCP price. The curves showing as-installed cost of RCP in

Figures 4.5 consider procuring RCP to three different project-site at distances of 70miles,

100 miles and 130 miles away from the manufacturing plant at 15% discount. The

manufacturers usually consider discount on listed prices in case of a large supply or on

the basis of long term business with pipe buyers. Three curves for as-installed cost of

81

HDPE which considered procuring granular backfiU @$10/CY, granular fiU @$15/CY

and Flex Base @$18/CY show clear savings over RCP. Fig. 4.6 compares as-installed

cost ofHDPE with fliat of RCP when RCP was considered to be procured to the site at

minimum pipe price of CSR Hydro Conduit and minimum pipe price at freight on board

condition (subsequently referred to as FOB) priced by Hanson Concrete Products. HDPE

appears to be cheaper again if granular backfill procured to the project-site @$10-

$15/CY. In Fig. 3.7, as-installed cost ofHDPE considering backfill price below $18/CY,

competes with as-installed cost of RCP which considered procuring RCP with discounted

minimum prices.

However, as-installed cost ofHDPE were maximum when cement stabilized

backfill @$60 and Flowable Fill @$85 were used in estimating. It can be inferred that if

the use of flowable backfill or high priced cement stabilized backfill can be substituted by

some kind granular backfill material locally available in the district of project site, HDPE

pipe can be an economically attractive stand in for RCP pipe.

Percent savings from using HDPE pipe as estimated in this analysis have been

listed in Table 4.16. Savings from using HDPE have been considered in comparison to

as-installed cost of RCP price for various RCP pipe price categories. The table speaks for

itself and leads to the fact that HDPE can be a suitable altemative of RCP under certain

resource price and availability conditions. Most of the numerals listed in Table 4.17 as

percent savings from HDPE over RCP lie between 10% and 15%. Maximum savings

appeared in this analysis is approximately 23% and minimum savings is 2.7%. In

general, it can be inferred from this analysis that if the backfill material that meets the

recommendation can be procured at a price lower than $20/CY, HDPE can compete with

RCP.

All the comparisons on resource prices and as-installed cost ofHDPE pipe and

RCP presented in this chapter are based on present-value-cost-data. A life cycle cost

analysis would would provide a more rational basis for cost comparison between HDPE

and RCP. However, data necessary for such analysis is not available because HDPE pipe

product that is currently available in the market has not been in use for many years. The

specification for the resin to be used for manufacturing HDPE pipe also demands change

82

within a short period of time due to its quality iiiq)rovements through research. These are

the reasons why a life cycle cost analysis for HDPE pipe installation was beyond the

scope of this research. Thus a con^arison based on as-installed cost ofHDPE pipe and

RCP in the only viable altemative at this time.

83

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90

CHAPTER 5

CONCLUSIONS

5.1 Introduction

The previous chapters in this thesis examined the use ofHDPE pipe in TxDOT

construction projects from two very important and practical viewpoints. One of these

two viewpoints involved the constructibility of the HDPE pipe system according to

specifications. Constructibility is an important aspect in large diameter HDPE pipe

because of its flexibility and dependence on surrounding backfill for strength to carry

imposed loads. As result, quality control during pipe installation deserve special

attention. This review, which was described in Chapter 3, examined the draft

specification from a constructibility standpoint and hence identified elements in the

specifications that may create difficulties during its field implementation. The final

specification that was developed by incorporating the recommendations from the

constructiblity review is found in this thesis as Appendix B. Another important issue that

affects the successful implementation of the new HDPE pipe specifications is economics.

Prior to using HDPE pipe in TxDOT projects, it was necessary to verify that that the

installation ofHDPE pipe according to new specifications is economically viable.

Therefore, in Chapter 4 of this thesis, necessary economic analyses were performed to

compare cost ofHDPE pipe installation with those of other traditional pipe products such

as RCP. As a part of tfiis analysis, bid prices for installation of HDPE, RCP and CMP

from highway agencies in other states were reviewed. A second comparison was

performed based on results from a sofhvare named 'PipePac 2000.' Subsequently, the

prices of two of the most important resources for pipe installation projects, i.e., pipe price

and backfill price were in various parts of Texas were compared. Finally, the above data

on pipe price and backfill price were incorporated into a more detailed analysis in which

as-installed costs ofHDPE and RCP were estimated and compared. Consequently, the

findings of that estimating were presented graphically in the concluding section of

Chapter 4. The findings showed that, in certain resource availability conditions, HDPE

pipe can provide significant economic benefit. The following sections document the final

91

conclusions and recommendations from the constructibility review and economic

analysis.

5.2 Conclusions

5.2.1 Conclusions: Constructibilitv Review

The constructibility review identified a number of deficiencies or problem areas

in that draft specification that required special attention. Revisions to overcome these

deficiencies were incorporated into a final specification dated August, 1999. These

revisions are summarized below:

a. Cement Stabilized Backfill is added as a third type of backfill that is acceptable

for use in HDPE pipe installations. In the final specifications this type of backfill

is identified as Type II backfill.. This revisions was based on the finding that

cement stabilized backfill is economically available and widely used in parts of

Texas, specially in TxDOT districts near the Gulf coast.

b. For Type II and III backfill materials that require compaction, wider minimum

trench widths are recommended to ensure there is adequate room to operate

commonly used compaction equipment. Recommended minimum trench widths

for HDPE pipes of 18", 24", 30", 36", 42" and 48" are listed in the final

specification.

c. A suitable gradation band for granular backfill materials was developed. This

gradation band is used in the new specifications in lieu of the previous backfill

material specifications that relied on Spec. Items 334 and 340 to define

gradation for granular backfill. The new gradation requirements are presented in

the final specification in a separate table. All the granular backfill materials that

fit in that gradation band are now referred to as Type III backfill,

d. The minimum backfill cover above the pipe crown is recommended to be revised

in the following manner as stated in the final specification (Appendix B, pp. 108-

109).

92

The backfill material shall be placed evenly and simultaneously on both sides of the pipe to not less than 300 mm (I ft) above the top of the pipe. No heavy construction equipment with axle loads equal to or larger than 40-kips shall be permitted to traverse the pipe trench. If the passage of such heavy construction equipment over an installed pipeline is necessary during construction, compacted fill in the form of a ramp shall be constructed to depth of one pipe diameter above the crown of the pipe.

5.2.2 Conclusions: Economic Analysis

The comparative economic analysis performed in Chapter 4 examined the

economic competitiveness ofHDPE pipe against the most widely accepted and used pipe

product, RCP. This analysis was based on all the present costs involved in initial

installation of the pipe system.. A more appropriate comparison between these two pipe

products would bebased on life cycle costs. Such an analysis, however, is not possible

because there is no adequate data on the performance and service life of the HDPE pipe

products that are currently available in the market. Therefore, it is beyond researchers

scope to observe or predict its performance of these pipe products in the future. As a

result, the conclusions made in this section is based on initial costs of pipe installation.

The findings from economic analysis can be summarized as follows.

a. As-installed bid prices ofHDPE and RCP in the projects undertaken by many

transportation agencies led to the important conclusion that allowing HDPE as a

biddable altemate along with RCP may result in significant savings.

b. Two most important resources that affect the overall project cost are pipe price

and backfill price. Data collected on pipe prices shows that HDPE pipe is

cheaper compared to RCP even though the number ofHDPE production plants

are fewer compared to that ofRCP manufacturing plants and the hauling

distances are longer. Also, HDPE pipe price does not vary for different supply

zone in Texas whereas RCP pipe price does vary with distance to supply zone.

However, HDPE pipe does require special kind of backfill material which often

has be obtained and transported to the project site at a cost.

c. A survey on availability of different backfill materials was performed prior to

93

estimating as-installed cost ofHDPE pipe and RCP required. It was found that

the price and availability of cement stabilized backfill shows a geographic

pattem in Texas districts. It is a readily and economically available backfill

material in the TxDOT districts along the gulf coast. The fiirther a district is

from the coast the higher its price is. Flowable fill appears to be most expensive

of all backfill materials. Flex Base and other granular backfill were found to be

a commonly available backfill material at comparatively low price.

In general, estimated as-installed costs ofHDPE was found to be cheaper than

as-installedcost ofRCP when flex base @ $18/CY, granular fill @$10/CY and

granular fill @$15/CY were used.. In this comparison, as-installed cost ofRCP

was estimated for the following cases: (i) When RCP is procured at minimum

price (freight on board), (ii) discounted minimum price and (iii) discounted

price applicable for a site 30-130 miles away from plant. Savings from using

HDPE pipe as estimated in the analysis were presented in Table 4.17 of Chapter

4. Most of the numbers listed in Table 4.17 as percent savings from HDPE over

RCP lie between 10% and 15%. Maximum savings obtained from this analysis

is approximately 23% and minimum savings is 2.7%. In general, it can be

inferred that if the backfill material that meets the recommendation can be

procured at a price lower than $20/CY, HDPE will be more economical than

RCP.

d. Even though the unit price of Flowable backfill is the highest of all ($85/CY) it

did not result in the maximum as-installed cost. This is due to the fact that

minimum trench width requirements for flowable backfill is smaller and

installation is faster. The cement stabilized backfill at $60/CY resulted in the

maximum as-installed cost.

5.3 Recommendations

Overall, this thesis has presented reviews of critical problems that might arise

during real world implementation of the specification developed for installation ofHDPE

pipe from two viewpoints: construction and economy. This research explored how

94

construction processes determine minimum dimensional requirements of trenches to be

excavated. The research on economic aspects ofHDPE pipe installation shows that

FIDPE can be competitive with other, traditional pipes in the larger diameter category

under many resource availability conditions. Based on the constructibility review and

economic analysis performed, the following final recommendations are made:

a. Based on analysis of actual as-installed cost data of statewide HDPE and RCP

pipe installation projects and estimated as-installed cost of several

hypothetical projects, it is recommended that HDPE should be accepted as a

biddable altemative.

b. The economic analysis was performed based on present value cost data of all

the resources. In future work, a life cycle cost analysis can be performed

which would consider the appropriate depreciation value ofHDPE pipe over a

period of time.

c. Developing an online 'Lessons Leamed Database' on constmction processes

and most recent price/availability picture of various resources is

recommended.

95

LIST OF REFERENCES

AASHTO, (1992). Standard Specification for Highwav Bridges. Edition 15, Section 18, "Soil-Thermoplasfic Pipe Interaction System," pp. 321-326.

Anderson, Stuart D., and Fisher, Deborah J. Constmctibility Review Process for Transtx)rtation Facilities Workbook. NCHRP Report 391, National Academy Press, Washington, D.C., 1997.

ASTM, D2321 (1993). "Standard Practice for Underground Installation of Thermoplasfic Pipe for Sewers and Other Gravity-flow Applicafions," ASTM Book of Standard. pp. 116-124.

Braden, Clay. RCP Price List, CSR Hydro Conduit, San Antonio, Texas, May 13, 1998.

Caterpillar Performance Handbook. Edition 26, CAT Publication by Caterpillar Inc., Peoria, Illinois, USA, October 1995.

Ellis, Tom. HDPE Pipe Price List, Quail Piping Products, Inc., Mangola, Arkansas, March 2000.

Freieich, David. HDPE Pipe Product Information, Hancors, Inc., Austin, Texas, 1998.

Gambatese, John A., and McManus, James F. "Constmctibility: A Quality Improvement Approach to Transportation Projects," Transportation Research Record 1575. Department of Civil Engineering, University of Washington, Seattle, Washington, D.C.,pp. 116-120.

Goddard, James B. Advanced Drainage Systems, Inc., Drainage Pipe: "The Sense and Dollars of Competition," Paper Presented at the 57th Annual Conference of N.Y.S.A.T.E., May 1997.

Haris, Frank. Modem Constmction and Ground Engineering Equipments and Methods. Second Edition, Longman Group Limited, UK, 1994.

Hunemuller, Brad. HDPE Pipe Price List, Advanced Drainage Systems, Inc., Round Rock, Texas, May 12,1999.

Jasek, Maria. Change Order Review, Yoakum District Office, Constmction Section, April 2000.

Killey, Martin D., and Allyn, Marques. National Constmction Estimator. 45th Edition, Craftsman Book Company, Carlsbad, California, 1997.

96

Kraemer, S., Ginley, D., and Joyce, C. The Life Cycle Analysis of Materials Competition for Pipe in the Constmction Industry. Bureau of Mines Information Circular No. 9279, United States De partment of the Interior.

Means Heavy Constmction Cost Data. Edition 13, R. S. Means, Kingston, Massachusetts, November 1998.

OSHA Regulations and Guidelines: A Guide for Health Care Provider, Standards - 29 CFR, Part 1926 Subpart P - Excavation, Thomson Learning, Florence, Kentucky, 2000.

Pmden, Dale. RCP Price List, Hanson Concrete Products, Inc., Dallas, Texas, May 13, 1999.

U. S. Army Corps. Of Engineers: "Biddability, Constmctibility, Operability, and Environmental Review," Regulation No. ER 415-1-11, Department of Army, Washington, D. C , September 1,1994.

Williams, Debbie. Change Order Review, Constmction Records, Laredo, April 2000.

Wilson, Robert, Chairman, Specification Committee: Statewide Special Specification 4269 (1993) and 4004 (1995), "Thermoplastic Pipe," Special Provision and/or Special Change Memorandum Dated March 15, 1996.

97

APPENDIX A

DRAFT SPECIFICATION FOR INSTALLATION OF

LARGE-DIAMETER HDPE DRAINGE

PIPE DATED MAY, 1998

98

DRAFT SPECIFICATIONS

HIGH DENSFFY POLYETHYLENE (HDPE) PIPE FOR GRAVFTY FLOW DRAINAGE APPLICATIONS

1. Description. This specification shall govern for the furnishing and installing of all 18 in (450 mm) to 48 in (1200mm)' high density polyethylene (HDPE) pipe used in the constmction of thermoplastic pipe culverts, sewer mains, laterals, stubs and inlet leads. The pipes shall be of the sizes, types, design and dimensions shown on the plans and shall include all connections and joints to new or existing pipes, sewer, manholes, inlets, headwalls and other appurtenances as may be required to complete the work.

2. Materials. Unless otherwise specified on the plans or herein, the HDPE pipes and fittings used for gravity flow drainage applications shall conform to the following specifications.

2.1 High density polyethylene pipes and fittings shall meet the requirements as in AASHTO M 294M-96 (for pipes up to 36 inches/900mm in diameter) and AASHTO MP6-95 (for pipes of 42 inches/1050mm and 48 inches/1200 mm in diameter).

2.2 Raw Materials - The pipes and the fittings shall be manufactured from virgin PE compounds which conform to the requirements of cell class 335420C^ as defined and described in ASTM D 3350, except that carbon black content shall not exceed 5 percent.

2.3 Designation of Type - The HDPE pipes used for gravity flow drainage applications shall be of Type S (outer cormgated wall with smooth inner liner) or Type D (inner and outer smooth walls braced circumferencially or spirally with projections or ribs).

2.4 Section Properties - Minimum wall thickness of the inner walls of Type S pipe and inner and outer walls of Type D pipe shall be as specified in Section 7.2.2 of the AASHTO M 294M-96 and MP6-95 respectively. The pipe stiffiiess at 5% deflection, when determined in accordance with ASTM designation D 2412, shall be as specified in Section 7.4 of AASHTO M 294M-96 and AASHTO MP6-95.

The manufacturer shall perform appropriate test procedures on representative samples of each type of pipe furnished, and hence verify that the pipe complies with the specifications. A certificate of compliance shall be prepared and submitted to the Department for review and approval. It shall include the following information: manufacturing plant, date of manufacture, pipe unit mass, material distribution, pipe dimensions, water inlet area, pipe stiffhess, pipe flattening, brittleness, environmental stress crack resistance, and workmanship.

' Nominal pipe size is the nominal inside diameter of the pipe ^ This new cell classification (i.e. 335420C) which is required in AASHTO Section 18 is a higher classification than that found in AASHTO M 294M-96 (i.e. 324420C).

99

3. Inspection. The quality of the materials, the process of manufacture, and the finished pipe shall be subject to inspection and approval by the Engineer at the manufacturing plant. In addition, the fmished pipe shall be subject to fiirther inspection by the Engineer at the project site prior to and during installation.

4. Marking. All pipe shall be clearly marked at intervals of not more than 12 ft (3.5 m), and fittings and couplings shall be clearly marked as follows:

4.1 Manufacturer's name or trade mark 4.2 Nominal size 4.3 Specification designation (e.g. M 294M-96) 4.4 Plant designation code 4.5 Date of manufacture

5. Joints. Joints shall be installed such that the connecfion of pipe sections will form a continuous line free from irregularities in the flow line. Joints shall meet the soiltightness definition in accordance with AASHTO Section 26.4.2.4. Suitable joints are the following:

5.1 Integral Bell-N-Spigot - The bell shall overlap a minimum of two cormgations of the spigot end when fully engaged. The spigot end shall have an O-Ring gasket that meets ASTM F 477: Specifications for Elastomeric Seals (Gaskets) for Joining Plastic Pipe.

5.2 Exterior Bell-N-Spigot_ - The bell shall be fully welded to the exterior of the pipe and overlap the spigot end so that flow lines and ends match when fully engaged. The spigot end shall have an O-Ring gasket that meets ASTM F 477: Specifications for Elastomeric Seals (Gaskets) for Joining Plastic Pipe.

6. Construction Methods. The location of private driveway and side road pipe shall be constructed at locations shown on the plans or as directed by the Engineer.

6.1 Excavation - All excavation shall be in accordance with the requirements of Item 400, "Excavation and Backfill for Stmctures."

The width of the trench for pipe installation shall be sufficient, but no greater than necessary, to ensure working room to properly and safely place and compact haunching and other embedment materials. The space between the pipe and trench wall must be wider than the compaction equipment used in the pipe zone.

When Type I backfill {See section 6.8 below) is used, the minimum trench width is the pipe outside diameter plus 12 inches (300 mm).

When Type n backfill {See section 6.8 below) is used, the minimum trench width is the pipe outside diameter times 1.25 plus 12 inches (300 mm). The contractor can use any trench width above the pipe zone.

6.2 Installation in Embankment - If any portion of the pipe projects above the existing ground level, an embankment shall be constmcted as shown in the plans or as directed by the Engineer for a distance outside each side of the pipe location of not less than five times the diameter and to a minimum elevation of 2 ft (0.6 m)

100

above the top of the pipe. The trench shall then be excavated to a width as specified in section 6.1 above.

6.3 Shaping and Bedding - The pipe shall be bedded in a foundation of compacted granular material that meets the gradation requirements of Type B, C, D or F aggregate mixtures in Item 334, "Hot Mix-Cold Laid Asphalt Concrete Pavements" and Item 340, "Hot Mix Asphalt Concrete Pavements." This material shall extend a minimum of 6 inches (150 mm) below the outermost cormgations or ribs and shall be carefully and accurately shaped to fit the lowest part of the pipe exterior for at least ten percent (10%) of the overall height. When requested by the Engineer, the Contractor shall furnish a template for each size and shape of the pipe to be placed for use in checking the shaping and bedding. The template shall consist of a thin plate or board cut to match the lower half of the cross section of the pipe.

6.4 Handling and Storage - Handling and Storage of HDPE pipe shall be in accordance with the pipe manufacturer's instmctions. Proper facilities shall be provided for hoisting and lowering the pipe into the trench without damaging the pipe or disturbing the bedding or the walls of the trench.

6.5 Laying Pipe — Unless otherwise authorized by the Engineer, the laying of pipe on the bedding shall be started at the outlet (or downstream) end and shall proceed toward the inlet (or upstream) end with separate sections firmly joined together. The pipe should be laid in conformity with the established line and grade and shall have a full, firm and even bearing at each joint and along the entire length of the pipe. The pipe should not rest on the bells at the end and therefore it may become necessary to excavate for the pipe bells. Any pipe which is not in alignment or which shows any undue settlement after laying shall be removed and relaid at the Contractor's expense.

Multiple installation of HDPE pipe shall be laid with the centerlines of individual barrels parallel. Unless otherwise indicated on the plans, the minimum clear distance between the outer surfaces of adjacent pipes shall be equal to 24 inches (600 mm).

6.6 Reuse of Existing Appurtenances - When exiting appurtenances are specified on the plans for reuse, the portion to be reused shall be severed from the existing culvert and moved to new position previously prepared, by approved methods.

Connections shall conform to the requirements for joining sections of pipes as indicated herein or as shown on the plans. Any headwalls and any aprons or pipe attached to the headwall that are damaged during moving operations shall be restored to their original condition at the Contractor's expense. The Contractor, if he so desires, may remove and dispose of the existing headwalls and aprons and constmct new headwalls at his own expense, in accordance with the pertinent specifications and design indicated on the plans or as furnished by the Engineer.

6.7 Sewer Connections and Stub Ends - Connections of pipe sewer to existing sewers or sewer appurtenance shall be as shown on the plans or as directed by the

Engineer. The bottom of the existing stmcture shall be mortared or concreted if necessary, to eliminate any drainage pockets created by the new connection. Where the sewer is connected into existing stmctures which are to remain in service, any damage to the existing stmcture resulting from making the connection shall be restored by the Contractor to the satisfaction of the Engineer. Stub ends, for connections to future work not shown on the plans, shall be sealed by installing watertight plugs into the free end of the pipe.

6.8 Backfilling - Backfill from the pipe bedding up to 1 ft (300 mm) above the top of the pipe is critical for the successfiil performance of the pipe. It provides necessary stmctural support to the pipe and controls pipe deflection. Therefore, special care should be taken in the placement and compaction of the backfill material. Special emphasis should be placed upon the need for obtaining uniform backfill material and uniform compacted density throughout the length of the pipe so that unequal pressure will be avoided. Extreme care should be taken to insure proper backfill under the pipe in the haunch zone.

Backfill material shall meet the following specifications.

Type I - Backfill consists of Special Specification Item 4005, "Flowable Backfill." The flowable backfill shall be placed across the entire width of the trench and shall maintain a minimum depth of 1ft (300 mm) above the pipe. A minimum of 24 hours shall elapse prior to backfilling the remaining portion of the trench with other backfill material in accordance with Item 400, "Excavation and Backfill for Stmctures."

Type n - Backfill consists of granular material that meets the gradation requirements of Type B, C, D or F aggregate mixtures in Item 334, "Hot Mix-Cold Laid Asphalt Concrete Pavements" and Item 340, "Hot Mix Asphalt Concrete Pavements." The backfill material shall be placed evenly and simultaneously on both sides of the pipe to not less than 1 ft (300 mm) above the top of the pipe. The backfill shall be placed in uniform layers not exceeding 8 inches (200mm) of thickness (loose measurement), wetted if required, and thoroughly compacted between the pipe and the side of the trench. Until a minimum cover of 1 ft (300 mm) is obtained, only hand operated tamping equipment will be allowed within vertical planes 2 ft (600 mm) beyond the horizontal projection of the outside surfaces of the pipe.

In the selection of appropriate backfill material, consideration should also be given to possible migration of fines from adjacent native soil materials into the backfill. Where potential for such migration exists, separation geotextiles that meet the requirements of ASSHTO M 288 Section 7 shall be installed between the native soil and the backfill.

6.9 Protection of Pipe - No heavy constmction equipment, such as earth hauling equipment shall be permitted to traverse the pipe trench until a minimum depth of cover above the pipe has been established. Unless otherwise specified on the

107

plans, the minimum depth of cover shall consist of fill compacted to a depth of at least one pipe diameter above the pipe.

Prior to adding each new layer of loose backfill material, until a minimum of I ft (300 nun) of cover is obtained, an inspection will be made of the inside periphery of the stmcture for local or unequal deformation caused by improper constmction methods. Evidence of such will be reason for such corrective measures as directed by the Engineer.

Pipe damaged by the Contractor shall be removed and replaced at no additional cost to the State.

7. _Measurement This item will be measured by the linear foot (meter). Such measurements will be made between the ends of the barrel along its flow line, exclusive of safety end treatments. Safety end treatments shall be measured in accordance with item 467, "Safety End Treatment". Where spurs, branches or connections to existing pipe lines are involved, measurement of the spur or new connecting pipe will be made from the intersection of its flow line with the outside surface of the pipe into which it connects. Where inlets, headwalls, catch basins, manholes, junction chambers, or other stmctures are included in lines of pipe, that length of pipe tying into the stmcture wall will be included for measurement but no other portion of the stmcture length or width will be so included.

For multiple pipes, the measured length will be the sum of the lengths of the barrels, measured as prescribed above.

This is a plans quantity measurement Item and the quantity to be paid for will be that quantity shown in the proposal and on the "Estimate and Quantity" sheet of the contract plans, except as modified by Article 9.8. If no adjustment of quantities is required additional measurements or calculations will not be required.

Flowable backfill will not be measured, but considered subsidiary to this item.

9. Payment The work performed and materials furnished in accordance with this Item and measured as provided under "Measurement" will be paid for at the unit price bid for "HDPE Pipe (Type I backfill)" of the type (if required) and size specified or "HDPE Pipe (Type I or EI backfill)" of the type (if required) and size specified. This price shall be the full compensation for furnishing, hauling, placing and joining of pipes; for all connections to new or existing stmctures; for moving and reusing headwalls where required, for removing and disposing of portions of existing stmctures as required; for the bedding and Type I or EI backfill material as required, for cutting of pipe ends on skew; and for all labor, tools, equipment and incidentals required to complete the work.

Excavation and backfill above the Type I or n backfill will be paid for in accordance with Item 400, " Excavation and Backfill for Stmctures". Safety end treatment will be paid for in accordance with Item 467, "Safety End Treatment".

103

APPENDIX B

FINAL SPECIFICATION FOR INSTALLATION OF

LARGE-DIAMETER HDPE DRAINGE

PIPE DATED AUGUST, 1999

104

DRAFT SPECIFICATIONS (Revised August 16, 1999)

HIGH DENSFTY POLYETHYLENE (HDPE) PIPE FOR GRAVrTY FLOW DRAINAGE APPLICATIONS

1. Description. This specification shall govern for the furnishing and installing of all 18 in (450 mm) to 48 in (1200mm)^ high density polyethylene (HDPE) pipe used in the constmction of thermoplastic pipe culverts, sewer mains, laterals, stubs and inlet leads. The pipes shall be of the sizes, types, design and dimensions shown on the plans and shall include all connections and joints to new or existing pipes, sewer, manholes, inlets, headwalls and other appurtenances as may be required to complete the work.

5. Materials. Unless otherwise specified on the plans or herein, the HDPE pipes and fittings used for gravity flow drainage applications shall conform to the following specifications.

5.1 High density polyethylene pipes and fittings shall meet the requirements as in AASHTO M 294-98 (for pipes up to 48 inches/1200mm in diameter).

5.2 Raw Materials - The pipes and the fittings shall be manufactured from virgin PE compounds which conform to the requirements of cell class 335420C as defined and described in ASTM D 3350, except that carbon black content shall not exceed 5 percent.

5.3 Designation of Type — The HDPE pipes used for gravity flow drainage applications shall be of Type S (outer cormgated wall with smooth inner liner) or Type D (inner and outer smooth walls braced circumferencially or spirally with projections or ribs).

2.4 Section Properties - Minimum wall thickness of the inner walls of Type S pipe and inner and outer walls of Type D pipe shall be as specified in Section 7.2.2 of the AASHTO M 294-98. The pipe stiffiiess at 5% deflection, when determined in accordance with ASTM designation D 2412, shall be as specified in Section 7.4 ofAASHTOM 294-98.

The manufacturer shall perform appropriate test procedures on representative samples of each type of pipe furnished, and hence verify that the pipe complies with the specifications. A certificate of compliance shall be prepared and submitted to the Department for review and approval. It shall include the following information: manufacturing plant, date of manufacture, pipe unit mass, material distribution, pipe dimensions, water inlet area, pipe stiffiiess, pipe flattening, brittleness, environmental stress crack resistance, and workmanship.

6. Inspection. The quality of the materials, the process of manufacture, and the finished pipe shall be subject to inspection and approval by the Engineer at the manufacturing plant. In addition, the finished pipe shall be subject to further inspection by the Engineer at the project site prior to and during installation.

Nominal pipe size is the nominal inside diameter of the pipe

7. Marking. All pipe shall be clearly marked at intervals of not more than 12 ft (3.5 m), and fittings and couplings shall be clearly marked as follows:

7.1 Manufacturer's name or trade mark 7.2 Nominal size 7.3 Specification designation (e.g. M 294-98) 7.4 Plant designation code 7.5 Date of manufacture

5. Joints. Joints shall be installed such that the connection of pipe sections will form a continuous line free from irregularities in the flow line. Joints shall meet the soiltightness definition in accordance with AASHTO Section 26.4.2.4. Suitable joints are the following:

5.1 Integral Bell-N-Spigot - The bell shall overlap a minimum of two cormgations of the spigot end when fully engaged. The spigot end shall have an O-Ring gasket that meets ASTM F 477: Specifications for Elastomeric Seals (Gaskets) for Joining Plastic Pipe.

5.2 Exterior Bell-N-Spigot - The bell shall be fully welded to the exterior of the pipe and overlap the spigot end so that flow lines and ends match when fully engaged. The spigot end shall have an O-Ring gasket that meets ASTM F 477: Specifications for Elastomeric Seals (Gaskets) for Joining Plastic Pipe.

6. Construction Methods. The location of private driveway and side road pipe shall be constmcted at locations shown on the plans or as directed by the Engineer.

6.9 Excavation - All excavation shall be in accordance with the requirements of Item 400, "Excavation and Backfill for Stmctures."

The width of the trench for pipe installation shall be sufficient, but no greater than necessary, to ensure working room to properly and safely place and compact haimching and other embedment materials. The space between the pipe and trench wall must be wider than the compaction equipment used in the pipe zone.

When Type I backfill {See section 6.8 below) is used, the minimum trench width is the pipe outside diameter plus 12 inches (300 mm).

When Type n or Type in backfill {See section 6.8 below) is used, the minimum trench width shall be as specified in Table 1. The contractor can use any trench width above the pipe zone.

6.10 Installation in Embankment - If any portion of the pipe projects above the existing ground level, an embankment shall be constmcted as shown in the plans or as directed by the Engineer for a distance outside each side of the pipe location of not less than five times the diameter and to a minimum elevation of 2 ft (0.6 m) above the top of the pipe. The trench shall then be excavated to a width as specified in section 6.1 above.

106

6.11 Shaping and Bedding - The pipe shall be bedded in a foundation of compacted granular material that is free of organic matter, clay lumps, and other deleterious matter. Such bedding material shall meet the gradation requirements shown in Table 2. This material shall extend a minimum of 6 inches (150 mm) below the outermost cormgations or ribs and shall be carefully and accurately shaped to fit the lowest part of the pipe exterior for at least ten percent (10%) of the overall height. When requested by the Engineer, the Contractor shall furnish a template for each size and shape of the pipe to be placed for use in checking the shaping and bedding. The template shall consist of a thin plate or board cut to match the lower half of the cross section of the pipe.

6.12 Handling and Storage - Handling and Storage of HDPE pipe shall be in accordance with the pipe manufacturer's instmctions. Proper facilities shall be provided for hoisting and lowering the pipe into the trench without damaging the pipe or disturbing the bedding or the walls of the trench.

6.13 Laying Pipe - Unless otherwise authorized by the Engineer, the laying of pipe on the bedding shall be started at the outlet (or downstream) end and shall proceed toward the inlet (or upstream) end with separate sections firmly joined together. The pipe should be laid in conformity with the established line and grade and shall have a full, firm and even bearing at each joint and along the entire length of the pipe. The pipe should not rest on the bells at the end and therefore it may become necessary to excavate for the pipe bells. Any pipe which is not in alignment or which shows any undue settlement after laying shall be removed and relaid at the Contractor's expense.

Multiple installation ofHDPE pipe shall be laid with the centerlines of individual barrels parallel. Unless otherwise indicated on the plans, the minimum clear distance between the outer surfaces of adjacent pipes shall be equal to 24 inches (600 mm).

6.14 Reuse of Existing Appurtenances - When exiting appurtenances are specified on the plans for reuse, the portion to be reused shall be severed from the existing culvert and moved to new position previously prepared, by approved methods.

Connections shall conform to the requirements for joining sections of pipes as indicated herein or as shown on the plans. Any headwalls and any aprons or pipe attached to the headwall that are damaged during moving operations shall be restored to their original condition at the Contractor's expense. The Contractor, if he so desires, may remove and dispose of the existing headwalls and aprons and constmct new headwalls at his own expense, in accordance with the pertinent specifications and design indicated on the plans or as furnished by the Engineer.

6.1 SSewer Connections and Stub Ends - Connections of pipe sewer to existing sewers or sewer appurtenance shall be as shown on the plans or as directed by the Engineer. The bottom of the existing stmcture shall be mortared or concreted if necessary, to eliminate any drainage pockets created by the new connection.

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Where the sewer is connected into existing stmctures which are to remain in service, any damage to the existing stmcture resulting from making the connection shall be restored by the Contractor to the satisfaction of the Engineer. Stub ends, for connections to future work not shown on the plans, shall be sealed by installing watertight plugs into the free end of the pipe.

6.\6Backfilling - Backfill from the pipe bedding up to 1 ft (300 mm) above the top of the pipe is critical for the successful performance of the pipe. It provides necessary stmctural support to the pipe and controls pipe deflection. Therefore, special care should be taken in the placement and compaction of the backfill material. Special emphasis should be placed upon the need for obtaining uniform backfill material and uniform compacted density throughout the length of the pipe so that unequal pressure will be avoided. Extreme care should be taken to insure proper backfill under the pipe in the haunch zone.

Backfill material shall meet the following specifications.

Type I - Backfill consists of Special Specification Item 4438, "Flowable Backfill." The flowable backfill shall be placed across the entire width of the trench and shall maintain a minimum depth of 1ft (300 mm) above the pipe. A minimum of 24 hours shall elapse prior to backfilling the remaining portion of the trench with other backfill material in accordance with Item 400, "Excavation and Backfill for Stmctures."

Type n - Backfill consists of Specification Item 400.6, "Cement Stabilized Backfill." Cement Stabilized Backfill shall be placed and compacted to ensure that all voids are filled completely.

Type m - Backfill consists of hard, durable, clean granular material that is free of organic matter, clay lumps, and other deleterious matter. Such backfill shall meet the gradation requirements shown in Table 2. The backfill material shall be placed evenly and simultaneously on both sides of the pipe to not less than 1 ft (300 mm) above the top of the pipe. The backfill shall be placed in uniform layers not exceeding 8 inches (200mm) of thickness (loose measurement), wetted if required, and thoroughly compacted between the pipe and the side of the trench. Until a minimum cover of 1 ft (300 mm) is obtained, only hand operated tamping equipment will be allowed within vertical planes 2 ft (600 mm) beyond the horizontal projection of the outside surfaces of the pipe.

In the selection of appropriate backfill material, consideration should also be given to possible migration of fines from adjacent native soil materials into the backfill. Where potential for such migration exists, separation geotextiles that meet the requirements of TxDOT Material Specification D9-6200, Type I shall be installed between the native soil and the backfill.

6.9 Protection of Pipe - No heavy constmction equipment with axle loads equal to or larger than 40-kips shall be permitted to traverse the pipe trench. If the passage of such heavy constmction equipment over an installed pipeline is necessary during

ins

constmction, compacted fill in the form of a ramp shall be constmcted to depth of one pipe diameter above the crown of the pipe.

Prior to adding each new layer of loose backfill material, until a minimum of 1 ft (300 mm) of cover is obtained, an inspection will be made of the inside periphery of the stmcture for local or unequal deformation caused by improper constmction methods. Evidence of such will be reason for such corrective measures as directed by the Engineer.

Pipe damaged by the Contractor shall be removed and replaced at no additional cost to the State.

7, Measurement This item will be measured by the linear foot (meter). Such measurements will be made between the ends of the barrel along its flow line, exclusive of safety end treatments. Safety end treatments shall be measured in accordance with item 467, "Safety End Treatment". Where spurs, branches or connections to existing pipe lines are involved, measurement of the spur or new connecting pipe will be made from the intersection of its flow line with the outside surface of the pipe into which it connects. Where inlets, headwalls, catch basins, manholes, junction chambers, or other stmctures are included in lines of pipe, that length of pipe tying into the stmcture wall will be included for measurement but no other portion of the stmcture length or width will be so included.

For multiple pipes, the measured length will be the sum of the lengths of the barrels, measured as prescribed above.

This is a plan quantity measurement Item and the quantity to be paid for will be that quantity shown in the proposal and on the "Estimate and Quantity" sheet of the contract plans, except as modified by Article 9.8. If no adjustment of quantities is required additional measurements or calculations will not be required.

Flowable backfill will not be measured, but considered subsidiary to this item.

9. Payment. The work performed and materials fumished in accordance with this Item and measured as provided imder "Measurement" will be paid for at the unit price bid for "HDPE Pipe (Type I backfill)" of the type (if required) and size specified or "HDPE Pipe (Type I, n or m backfill)" of the type (if required) and size specified. This price shall be the fiill compensation for furnishing, hauling, placing and joining of pipes; for all connections to new or existing stmctures; for moving and reusing headwalls where required, for removing and disposing of portions of existing stmctures as required; for the bedding and Type I, n or m backfill material as required, for cutting of pipe ends on skew; and for all labor, tools, equipment and incidentals required to complete the work.

Excavation and backfill above the Type I, II or m backfill will be paid for in accordance with Item 400, " Excavation and Backfill for Stmctures". Safety end treatment will be paid for in accordance with Item 467, "Safety End Treatment".

109

TABLE 1. Minimum Trench Width

Nominal Pipe Diameter inches

18 24 30 36 42 48

mm 450 600 750 900 1050 1200

Minimum Trench Width inches

44 54 66 78 84 90

mm 1100 1350 1650 1950 2100 2250

TABLE 2. Gradation Requirements for Type m BackfiU Material

Sieve No.

1 inch % inch Vi inch ^1% inch No. 4 No. 10 No.200

Percent Retained (Cumulative)

0-5 0-35 0-75 0-95

35-100 50-100 90-100

Note: Material that qualify under the following TxDOT specifications may meet the gradation requirements specified in this table.

1. ITEM 247: FLEXIBLE BASE, Grades 1,4 and 5. 2. FTEM 421: PORTLAND CEMENT CONCRETE, Coarse Aggregate Grades 4, 5, 6, 7 and 8. 3. FTEM 556: PIPE UNDBRDRAINS, Filter Material Type B

110

APPENDIX C

TYPES OF BACKFILL MATEIUALS ECONOMICALLY

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APPENDIX D

WORK BREAKDOWN STRUCTURE: ITEMIZING MAJOR

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120

APPENDIX E

ESTIMATING AS-INSTALLED COSTS OF

HDPE AND RC PIPE

121

Pip

e D

iam

eter

(in

ch

) P

IPE

AN

D T

RE

NC

H D

IME

NS

ION

FO

R H

DP

E

PIP

E I

NS

TALL

TIO

N

CO

CN

CD CO

O CO

CN

CO

Nom

inal

Pip

e D

iam

eter

(in

.)

52.7

46

.75

42.4

6 36

.07

27.8

21

.2

Pip

e O

uter

Dia

met

er (

in.)

O OJ

CO

00

co CO

in

Min

imum

Tre

nch

Wid

th (

in.),

(f

or T

ype

II &

Typ

e III

Bac

kfill)

64

.7

58.7

5 54

.46

48.0

7 39

.8

33.2

M

inim

um T

renc

h W

idth

(in

.),

(for

Flo

wab

le

Bac

kfill

) 70

.7

64.7

5 60

.46

54.0

7 45

.8

39.2

M

inim

um T

renc

h D

epth

in.

200

220

240

140

140

o

Tota

l Le

ngth

of

HD

PE

Pip

e (m

) 65

6 72

1.6

787.

2 45

9.2

459.

2 55

7.6

Tot

al L

engt

h of

HD

PE

Pip

e (ft

)

EX

CA

VA

TIO

N F

OR

HD

PE

PIP

E

INS

TALL

ATI

ON

10

73.5

926

1009

.46

954.

8201

48

421.

4789

9 29

2.10

2222

2 24

7.36

3292

2 T

otal

Vol

ume

to b

e E

xcav

ated

in C

Y (

for T

ype

II &

Typ

e III

Bac

kfill

) 77

1.79

379

706.

0215

66

6.66

0324

30

6.97

72

215.

2901

564

186.

6468

477

Tot

al V

olum

e to

be

Exc

avat

ed in

CY

(for

Fl

owab

le B

ackf

ill)

705.

7445

3 69

1.03

84

668.

2780

31

300.

8539

2 22

0.44

9140

8 19

6.76

4763

6 T

otal

Bac

kfill

Mat

eria

l R

egui

red

in C

Y (

Typ

e 1

and

II U

sed)

40

3.94

573

387.

5994

38

0.11

8207

18

6.35

213

143.

6370

75

136.

0483

192

Tot

al B

ackf

ill M

ater

ial

Reg

uire

d in

CY

(F

low

able

Fill

Use

d)

2C

Y

1..5

1.

5 C

Y

1.5

CY

>-O

>-

o T—

Exc

avat

or C

apac

ity (

Bac

khoe

l)

o 00

o

o

o

co in

CO in

Exc

avat

ion

Rat

e in

CY

/hr

13.4

1990

7 14

.420

86

13.6

4028

78

6.02

1128

4 5.

5113

6268

3 4.

6672

3192

8 T

otal

Tim

e R

egui

red

for

Exc

avat

ion

in h

r fB

ackf

ill T

voe

II or

III

Use

d)

9.64

7422

3 10

.086

02

9.52

3718

91

4.38

5388

5 4.

0620

7842

2 3.

5216

3863

7 T

otal

Tim

e R

egui

red

for

Exc

avat

ion

in h

r rF

low

able

Fill

Use

d)

122

^3

.i o U

IS H

Pip

e D

iam

eter

(in

ch)

CO

CN

CD CO

O CO

CN

CO

CA

LCU

LATI

NG

TO

TA

L B

US

Y H

OU

RS

OF

E

AC

H E

QU

IPM

EN

T I

N C

AS

E O

F H

DP

E P

IPE

IN

STA

LLA

TIO

N

2.5

CY

2.

5 C

Y

2.5

CY

2.

5 C

Y

2.5

CY

2

.5C

Y

Cap

acity

of t

he O

ther

Bac

khoe

2 10

0 10

0 10

0 10

0

o CO

100

Bac

kfill

ing

Rat

e of

Bac

khoe

2 in

CY

/hr

7.05

7445

3 6.

9103

84

6.68

2780

3 3.

0085

392

2.75

5614

26

1.96

7647

6 T

otal

Tim

e R

egui

red

for

Bac

kfill

ing

in h

rs (

Typ

e II

& I

II B

ackf

ill U

sed)

4.

0394

573

3.87

5994

3.

8011

820

1.86

3521

3 1.

7954

6343

1.

3604

831

Tot

al T

ime

Reg

uire

d fo

r B

ackf

illin

g in

hrs

(F

low

able

Fill

Use

d)

CN

CN

CN

O

O

O

Wid

th o

f Vib

rato

ry P

late

Com

pact

or o

r T

empi

ng

Ram

mer

(in

.)

1.6

1.6

CD

1.61

0.

61

0.61

R

ate

of C

ompa

ctio

n in

CY

per

min

at

8 in

Lift

per

T

wo

Com

pact

ors

7.35

1505

5 7

1983

17

6.96

1229

4 3.

1144

298

6.02

3200

56

5.37

6086

4 T

otal

Tim

e R

egui

red

for

Com

pact

ion

in h

rs

(incl

udes

tren

ch b

otto

m)

CD

CD T—

CO

CD X—

CO

CO

Leng

th o

f Tre

nch

Box

es in

ft

(Siz

e 16

by

6 ft)

^

45.1

49

.2

28.7

28

.7

34.8

5 T

otal

No.

of

Rep

etiti

on in

Ins

talla

ing

Tre

nch

Box

es

TT

-

r

TT

CO

"

Tim

e R

egui

red

for

Eac

h T

renc

h B

ox I

nsta

llatio

n in

m

in

2.73

3333

3 3.

0066

67

3.28

1.

9133

333

1.43

5 2.

3233

333

Tot

al T

ime

Reg

uire

d fo

r A

ll R

epea

ted

Tre

nch

Box

In

stal

latio

n in

hrs

32

.8

36.0

8 39

.36

22.9

6 22

.96

27.8

8 T

otal

No.

of

HD

PE

Pip

es E

ach

20 f

t Lon

g 31

.8

35.0

8 38

.36

21.9

6 21

.96

26.8

8 T

otal

No

of J

oint

s W

hen

HD

PE

Pip

e is

Use

d

t^

r--

co

CO

in

in

Tim

e R

egui

red

forT

iein

g,

Lifti

ng,

Layi

ng a

nd

Join

ginq

of

Eac

h P

ipe

in m

in

3,82

6666

7 4.

2093

33

3.93

6 2.

296

1.91

3333

33

8888838 3

Tot

al T

ime

Reg

uire

d fo

r Li

fting

, La

ying

and

Joi

ning

of

All

the

Pip

es in

hrs

15

.455

322

15.9

2596

15

.639

087

7.99

648

7.60

9747

73

7.95

8335

9 C

umul

ativ

e B

usy

hrs

of B

ackh

oe2

(Whe

n B

ackf

ill

II &

III

Use

d)

10.5

9945

7 11

.091

99

11.0

1718

2 6.

0728

546

5.14

3796

77

6.00

7149

8 C

umul

ativ

e B

usy

hrs

of B

ackh

oe2

(Whe

n F

low

able

Fill

Use

d)

123

T3 <L)

o O

Pip

e D

iam

eter

(Inc

h)

00

CN

CD CO

O CO

CN

00

CA

LCU

LATI

NG

TO

TA

L W

AG

E A

ND

EQ

UIP

ME

NT

C

OS

T F

OR

HD

PE

PIP

E I

NS

TALL

ATI

ON

P

RO

JEC

TS

CN

CN

CN

App

roxi

mat

e P

roje

ct D

urat

ion

in d

ays

(For

Typ

e II

&

II ba

ckfil

l or

Flo

wab

le F

ill)

CN

CN

CN

CN

CN

CN

Tota

l N

o. o

f E

xtra

Lab

orer

s fo

r C

ompa

ctio

n, P

ipe

layi

ng a

nd J

oini

ng

o CO

o CO

o CO

o CO

o CO

o CO

Labo

rer's

Wag

e pe

r H

our

960

960

960

480

480

480

Tot

al C

ost f

or L

abor

er's

Wag

e fo

r P

roje

ct D

urat

ion

Tim

e

in CO

in CO

in CO

in CO

o CO

o CO

Ren

tal

Rat

e of

Com

pact

or (

dolla

rs p

er d

ay)

140

140

140

o

o CD

o CD

Cos

t for

Ren

ting

Two

Com

pact

ors

for

Pro

ject

D

urat

ion

Tim

e 10

0 10

0 10

0 10

0 10

0

o o

Ren

tal

Rat

e of

eac

h 16

ft

by 6

ft t

renc

h bo

x (d

olla

rs

per

day)

60

0 60

0 60

0 30

0 30

0 30

0 C

ost f

or R

entin

g Th

ree

Tre

nch

Box

es fo

r P

roje

ct

Dur

atio

n

CD 00

CD in

CD in

CD in

CD

CD

Hou

rly R

enta

l R

ate

of B

ackh

oel

(1 C

Y,

1.5

CY

or 2

C

Y B

ucke

t C

apac

ity)

100

100

100

100

100

100

Hou

rly R

enta

l R

ate

of B

ackh

oe2

(2.5

CY

Buc

ket

Cao

acitv

) 35

.41

35.4

1 35

.41

35.4

1 35

.41

35.4

1 H

ourly

Wag

e of

81

Cre

w (

1 T

ract

or o

pera

tor

1 la

bore

r) i

nvol

ved

with

Bac

khoe

s 12

1.41

91

.41

91.4

1 91

.41

81.4

1 81

.41

Hou

rlly

Tot

al I

nsta

llatio

n C

ost

Invo

lved

with

B

ackh

oel

135.

41

135.

41

135.

41

1

135.

41

135.

41

135.

41

Hou

rlly

Tot

al I

nsta

llatio

n C

ost

Invo

lved

with

B

ackh

oe2

1942

.56

1462

.56

1462

.56

731.

28

651.

28

651.

28

Tot

al C

ost

Invo

lved

with

Bac

khoe

l fo

r P

roje

ct

Dur

atio

n T

ime(

All

Tvo

es o

f B

ackf

ill)

2166

.56

2166

.56

2166

.56

1083

.28

1083

.28

1083

.28

Tot

al C

ost

Invo

lved

with

Bac

khoe

2 fo

r P

roje

ct

Dur

atio

n T

ime(

AII

type

s of

bac

kfill)

124

t 3 <D

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U

x: o

(D <4—•

CD

E ro

b <D CL

Q-

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CN -^

CD CO

o CO

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rice

of N

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i n CO

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) Fill

($/

CY

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Type

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42

48

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48

83.2

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41.7

7383

13

31.5

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d 79

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92

68.4

798

53.3

6548

42

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04

30.6

7892

96

22.2

0931

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t of

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n C

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t S

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d 11

0.11

51

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128

PERMISSION TO COPY

In presenting this thesis in partial fulfiUment of the reguirements for a

master's d e ^ e e at Texas Tech University or Texas Tech University Health Sciences

Center, I a ^ e e that the Library and my major department shall make it freely

available for research purposes. Permission to copy this thesis for scholarly

purposes may be pan t ed by the Director of the Library or my major professor.

It is understood that any copying or publication of this thesis for financial gain

shall not be allowed without my further written permission and that any user

may be liable for copyright infringement.

Agree (Permission is granted.)

Student's Signature L)ate

Disagree (Permission is not granted.)

Student's Signature Date

hdpe drainage pipe a thesis - tdl

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