retaining walls: stability analysis and construction
TRANSCRIPT
USE OF TIRE BALES IN BUILDING EARTH
RETAINING WALLS: STABILITY ANALYSIS
AND CONSTRUCTION GUIDELINES
by
MOHAMMAD SADIQUE HOSSAIN, B.S.C.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
Appnbved
Accepted
December, 2000
ACKNOWLEDGEMENTS
I would like to express my gratitude to Dr. Priyantha W. Jayawickrama for
chairing my thesis committee. I greatly appreciate his guidance and support throughout
the research project. I would also like to thank him for all the knowledge and skills that I
learned from his geotechnical engineering classes. I am also thankful to Dr. Mujahid H.
Akram for being on my thesis committee.
I would like to express my eternal gratitude to my parents for their affection,
guidance, support and sacrifice for me. I am also thankful to my wife whose love and
support made me accomplish my task.
11
TABLE OF CONTENTS
ACKNOWLEDGEMENTS ii
ABSTRACT vi
LIST OF TABLES vii
LIST OF FIGURES viii
CHAPTER
I. INTRODUCTION 1
1.1 Overview 1
1.2 Significance of Used Tire Problem 1
1.3 Current Applications of Scrap Tires 2
1.3.1 Energy Recovery 2
1.3.2 Tire Pyrolysis 2
1.3.3 Retreading 3
1.3.4 Scrap Tires in Civil Engineering Applications 3
1.3.4.1 Wet Poured Layers 3
1.3.4.2 Rubber Modified Asphalt 3
1.3.4.3 Marine Reefs and Shoreline protection 4
1.3.4.4 Earth Retaining and Erosion Control Structures 4
1.4 Objective and Scope of the Research Project 4
II. LITERATURE REVIEW 6
2.1 Overview 6
2.2 Eco-Bloc in the construction of Retaining Walls 6
2.2.1 Eco-Bloc 6
2.2.2 Different Types of Eco-Bloc 8
2.2.2.1 Bulkhead/Erosion Control 8
2.2.2.2 Perimeter Wall 8
2.2.3 Design Criteria 8
2.2.3.1 Design of the Unit 10
2.2.4 Different Applications of Eco-Bloc 14
2.2.5 Features and Benefits of Using Eco-Bloc in Retaining Walls.. 14
iii
2.2.6 Economics of Construction by Eco-Bloc 16
2.3 Encore Tire Bales in the Construction of Retaining Walls 16
2.3.1 Encore Baler 16
2.3.2 Summary of Test Results on Encore Tire Bale 19
2.3.3 Benefits ofUsing Baled Whole Tires 19
2.3.4 Costs of Baler 19
2.3.5 Different Applications of Baled Tires 20
2.3.5.1 ABrief Description of Carlsbad, NM Project 21
III. STABILITY ANALYSIS AND DESIGN OF RETAINING WALL 25
3.1 Overview 25
3.2 Eco-Bloc Tire Retaining Walls 25
3.2.1 Modes of Failure 25
3.2.1.1 External Stability 28
3.2.1.2 Internal Stability 30
3.2.2 Stability Analysis and Design of Retaining Wall 32
3.3 Encore Tire Bale Retaining Walls 42
3.3.1. Modes of Failure 42
3.3.2 Stability Analysis 42
IV. DESIGN CHARTS AND SPECIFICATIONS 43
4.1 Overview 43
4.2 Selection of Design parameters 43
4.2.1 Wall Configurations 43
4.2.2 Site and Loading Conditions 44
4.2.3 Earth Reinforcement Systems 44
4.2.4 Soil Parameters 45
4.3 Design Charts 45
4.3.1 Design Charts for Eco-Bloc Retaining Wall 46
4.3.2 Design Charts for Encore Bale Retaining Wall 46
4.4 Construction Costs for Tire Retaining Walls 61
4.5 Construcfion Techniques for tire retaining walls 63
IV
V. CONCLUSIONS AND RECOMMENDATIONS 66
5.1 Conclusions 66
5.2 Recommendations 66
BIBLIOGRAPHY 68
ABSTRACT
In the United States, about 270 million automobile and truck tires are sold each
year, with most of those tires eventually making a trip to the landfill, adding to the
existing inventory of about 400 million. This thesis presentation focuses on the possible
use of tire bales for building retaining walls. Tire bales are scrap tires compressed to a
reduced volume. Two types of tire bales that have been used for different purposes were
identified in the literature review. They are Eco-Bloc and En-Core Tire Bales. The tire
bales can be used for building mechanically stabilized earth and gravity retaining walls.
Detailed stability analysis and design was done for these two types of retaining walls.
The stability analyses investigated both external and internal failure modes. Repeated
analysis was done for different site and loading conditions, different wall configurations
and different soil parameters. After all the design combinations were put into design, the
designs were combined to form design charts. These charts may be used in projects that
match the site and loading descriptions provided in the charts. Some construction
guidelines are provided to assist in constructing the retaining walls. It is recommended
that full-scale test walls of both mechanically stabilized and gravity retaining wall be test-
built before their commercial use. The fiill-scale tests should enable the constructability
review, economic analysis and environmental impact analysis to be done.
VI
LIST OF TABLES
2.1 Engineering Properties of Single Unit -Steel Reinforced 11
2.2 Engineering Properties of Single Unit -Plain Concrete 11
4.1 Mechanically Stabilized Earth Wall for Soil Fricfion Angle of 25^ to 30^ (Reinforcement Type: Metal Strip) 47
4.2 Mechanically Stabilized Earth Wall for Soil Friction Angle of 30^ to 35^ (Reinforcement Type: Metal Strip) 48
4.3 Mechanically Stabilized Earth Wall for Soil Fricfion Angle of 25^ to 30^ (Reinforcement Type: Geotextile/Geogrid) 52
4.4 Mechanically Stabilized Earth Wall for Soil Fricfion Angle of 30^ to 35^ (Reinforcement Type: Geotextile/Geogrid) 53
4.5 Gravity Retaining Wall for Soil Fricfion Angle of 25^0 35^ 57
Vll
LIST OF FIGURES
2.1 Compressed Tires 7
2.2 Interlocking Design of Eco-Bloc™ 7
2.3 Oblique View of Eco-Bloc™ Unit 9
2.4 Eco-Bloc™ Reinforcing using Welded Wire Fabric 12
2.5 Eco-Bloc™ Reinforcing using No. 3 Rebar 12
2.6 Eco-Bloc ^ using Plain Concrete 13
2.7 Walls using Eco-Bloc Units 15
2.8 River Wing dam Built using Eco-Blocs 15
2.9 Tires being loaded in the Baler 17
2.10 Tires Being Compressed in the Baler 18
2.11 Finished Bale being Ejected from the Baler 18
2.12 Tire Bales as Subgrade Lightweight Fill for Road Construction 21
2.13 Erosion in Lake Carlsbad 22
2.14 Tire Bales on Top of Concrete Foundation 23
2.15 Encapsulation of Bales in Concrete 23
2.16 Block Retaining Wall on Top of Bales 24
3.1 Typical MSE Wall Construcfion using Eco-Bloc™ Units 26
3.2 Gravity Retaining Walls of Different Shape 27
3.3 External Stability Failure Mechanisms of MSE Retaining Walls 29
3.4 Internal Stability Failure Mechanisms of MSE Retaining Walls 31
3.5 Coulomb's Active Earth Pressure 35
3.6 Tensile Forces in the Reinforcements and Schematic Maximum 37 Tensile Force Lines: (b) inextensible reinforcements, (c) Extensible reinforcements
4.1 MSE Wall using metal strips with Horizontal Backfill and no Surcharge 49
4.2 MSE Wall using metal strips with Horizontal Backfill and 500 Ib/ft Surcharge 50
Vlll
4.3 MSE Wall using metal strips with 15^ Sloping Backfill and no Surcharge 51
4.4 MSE Wall using geosynthetics with Horizontal Backfill and no Surcharge 54
4.5 MSE Wall using geosynthefics with Horizontal Backfill and 500 Ib/fl Surcharge 55
4.6 MSE Wall using geosynthefics with 15^ Sloping Backfill and no Surcharge 56
4.7 Gravity Walls of Different Shape with Horizontal Backfill and no Surcharge 58
and 500 Ib/ft Surcharge 59 4.8 Gravity Walls of Different Shape with Horizontal Backfill
rg'
4.9 Gravity Walls of Different Shape with 15^ Sloping Backfill and no Surcharge 60
IX
CHAPTER I
INTRODUCTION
1.1 Overview
Throughout the United States, millions of waste tires are being generated each
year. These huge dumps of waste tires represent an enormous depot of lost energy,
materials, and money. Moreover, waste fires present a number of environmental, health
and safety hazards to the public and represent a serious public nuisance. While scrap fires
represent only 1.8% of the total solid waste stream in industrialized countries (1),
problems associated with scrap fires get a disproportionate amount of attention. The
hazards most commonly posed by the unsafe disposal or scrap tires are fire hazard and
mosquito breeding.
1.2 Significance of Used Tire Problem
According to the Rubber Manufacturers Associafion, in 1998, 270 million tires
were generated in the United States. Approximately 66 percent of these scrap tires were
productively used or recycled. Another 12 percent were placed in landfill or monofill.
Estimates also indicate that the current stockpile of scrap tires in the US is around 400
million. Scrap tires create unique problems in landfill disposal; not only because of their
large numbers but also because of the nature and properties of their chief component,
rubber. Rubber tires are difficult to compact in landfills because they tend to rise and
even pop through the groundcover as other waste materials compact around them. Their
buoyancy causes them to rise to the surface after rainfall leaving behind empty spaces
that damages the landfill's stable, carefully layered composition. In addition, the hollow
shape of the tires fills with decomposition gases creating a serious fire hazard. Experience
has shown that large tire fires can bum for weeks causing the rubber to decompose into
oil, which may pollute ground and surface water, as well as gas and carbon black.
Moreover, the tire rubber is a dense, durable and elastic material that does not undergo
natural decomposition in landfill environment easily. Rainwater accumulates in tire piles
creafing an ideal environment for mosquitoes, which are known to transmit disease to
1
humans. Because of all these reasons, many landfills do not accept large quantities of
discarded tires, while others charge a high tipping fee for their disposal. Consequently,
scrap tires are frequently placed in dedicated stockpiles or in illegal tire dumps.
1.3 Current Applications of Scrap Tires
Presently, approximately 66 percent of scrap tires are being used in retreading,
recycling, and energy recovery applications or in Civil Engineering applications (1).
1.3.1 Energy Recoverv
Tires can be burnt for energy recovery. Tires are burned for fuel in power plants,
tire-manufacturing plants, cement kilns, pulp and paper plants and small steam generators
utilizing a combustion technology similar to that for coal. In the U.S., approximately 114
million scrap tires were used as fuel supplement in power plants, cement kilns, industrial
boilers, etc., in 1998 (1). Tire Derived Fuel (TDF) is currently the most widely used
disposal method for scrap tires. TDF is defined as a scrap tire that is shredded and
processed into a rubber chip with a range in size and metal content. Size normally varies
in a range of 2 inches to 4 inches and metal content ranges from wire free, to relatively
wire free, to only bead wire removed, to no wire removed (1). Depending on the amount
of wire removed, the TDF has an energy content ranging from 14000 Btu/lb. to 15000
Btu/lb (2). Combustion efficiency for TDF is generally understood to be in the 80% range
(3). Hence, the re-use of scrap tires as tire derived fuel is generally considered to be one
of the more promising approaches to solve the scrap tire disposal problem.
1.3.2 Tire Pvrolvsis
Pyrolysis is the thermal decomposition of an organic material under the exclusion
of ambient oxygen. The typical products of scrap tire pyrolysis are: hydrocarbon gases
and oils, low-grade carbon black and steel. Pyrolysis plays only a marginal role in the
scrap tire industry because the oil and gas produced in this method needs to compete with
the low prices of conventional fuel.
1.3.3 Retreading
One form of tire recycling that has been in use for many years consists of tire
retreading. But available data indicates that retreading of old tires for reuse has steadily
declined in the US, particularly in the recent years. The decline in retreaded tire market
has been partly attributed to the complex technologies used in the production of modem,
high quality tires. As a result, the retreading of tires with new designs has become a less
profitable business.
1.3.4 Scrap Tires in Civil Engineering Applications
Scrap tires are used in different ways in Civil Engineering Applications. Civil
Engineering projects utilizing scrap tires typically involve replacing conventional
construction material (e.g., road fill, gravel, sand or dirt) with whole scrap tires or tire
chips. In their whole form, tires are used in crash barriers, reef, and shore protection and
in retaining walls. Whole tires are now being used to prevent soil erosion. Tires are also
used as fill. Cmmb mbber is being used in highway applications including the
improvement of asphalt.
1.3.4.1 Wet Poured Layers
Playgrounds and athletic surfaces are frequently covered with a layer of mbber
granules in order to help prevent injuries. Many high schools throughout the U.S. use
mnning tracks that consist of recycled material. Most commonly, a moisture-curing
urethane is mixed with ground tire mbber (GTR) and applied in a similar way as other
poured pavements. These layers are usually softer than molded mats and the top layer can
be colored.
1.3.4.2 Rubber Modified Asphalt (RMA)
Adding recycled tire mbber to the hot asphalt mix is a very economical way of
meeting, or exceeding, the new SHRP specifications that require certain physical
properties that rarely can be met by conventional (unmodified) asphalt cements. RMA
can significantly widen the temperature span of asphalt pavements when compared to
conventional asphalt binders. Increased resistances to mtting, reflective and thermal
cracking are the main benefits of RMA. Other advantages include better de-icing
properties, reduced traffic noise and, most importantly, a significantly increased service
life and thus a lower life cycle cost.
1.3.4.3 Marine Reefs and Shoreline Protection
Artificial reefs are used in the marine environment to duplicate conditions that
cause concentrations of fish and invertebrate on natural reefs. Scrap tires have been used
for shoreline protection since the 1970's. Breakwaters are offshore barriers that protect a
harbor or shore fi-om the strong impact of waves. Scrap tires for breakwaters and floats
are filled with material, usually foam, which displaces of water.
1.3.4.4 Earth Retaining and Erosion Control Stmctures
Whole scrap tires have been used in a variety of earth retaining and erosion
control stmctures across the world. Some of these stmctures have used whole tires filled
with soil or gravel as the basic building unit. Some others have used baled tires that are
produced by compressing a large number of tires and binding them together. One
example of such earth retaining stmctures includes retaining walls for erosion control
using Eco-Bloc units made by Ecological Building Systems. Another instance of tire bale
use is erosion control and dam constmction using En-Core baler, a tire baler produced by
ENCORE SYSTEMS, inc. Some examples of earth retaining stmctures using whole
scrap tires include: (a) ECOFLEX tire retaining wall system developed by SULCAL
Constmction Pvt. Ltd., in Australia; (b) USD A tire-faced reinforced earth retaining wall;
(c) ECO WALL highway noise barrier in Vienna, Austria; and (d) Santa Barbara Public
Works Department's earth retaining stmcture.
1.4 Objectives and Scope of the Research Project
Although earth retaining stmctures have been built using discarded tires by a
number of agencies as isolated constmction projects, general design guidelines applicable
for a wide range of wall heights, wall configurations and backfill material types are not
available at the present time. The primary objective of this research project is to develop
such guidelines so that used tires can be utilized in routine retaining wall constmction
projects by the transportation industry. Such retaining walls should be capable of
withstanding lateral earth pressures from the soil backfill as well as any surcharge loads
that is typically found in an urban setting. It is equally important that the wall, once
completed, has an aesthetically pleasing appearance.
The general research approach used to accomplish the research objectives stated
above consisted of the following steps:
• Collect information from previous/on-going tire retaining wall projects. This
information will include tire retaining wall configurations, designs, equipment
requirements and any specific problems encountered.
• Review and analyze the information collected and hence come up with a number
of tentative designs that will meet TxDOT (sponsor agency of the research
project) needs.
• Perform necessary stability analysis to ensure that the selected tire wall designs
have adequate factor of safety against potential modes of failure. Such analysis
examined intemal stability criteria such as mpture and pullout of backfill
reinforcement and then external stability conditions such as overtuming, sliding
and bearing capacity failure.
• Perform repetitive design calculations for walls with varying configurations,
heights and backfill material properties and loading conditions and hence develop
design charts. The design charts should enable someone to readily select wall
configurafion without going through detailed experiments and calculations.
CHAPTER n
LITERATURE REVIEW
2.1 Overview
This project involved a survey of different Civil Engineering applications of
waste tires throughout the world. The survey included a comprehensive library search, a
telephone survey and an Intemet search. The primary purpose of the search was to
identify some suitable techniques to build retaining walls utilizing tire bales. Retaining
walls and River Wing dams have been built utilizing compressed tire bales named Eco-
Bloc. Retaining walls for erosion control have been built using tire bales produced by
Encore Systems, Inc. The findings about the Eco-Bloc and Encore Baler are presented in
this chapter. The other aspect of the project was the use of whole tires for building
retaining walls. That issue has been addressed in a separate task.
2.2 Eco-Bloc'^^ in the Constmction of Retaining Walls
2.2.1 Eco-Bloc™
Eco-Bloc is a trademark of Ecological Building Systems (EBS), which is
headquartered in Cypress, Texas. EBS has developed a patented process for using a bale
of compressed scrap tires as a core for a stmctural concrete building product called the
Eco-Bloc."^^ It has been designed and manufactured for Civil Engineering applications
like erosion control, retaining walls, border walls, prison walls, river wing dams, etc.
Eco-Bloc' ' is an integration of baled compressed tires with concrete and reinforcement
steel to form a sealed concrete unit. The compressed tires are encapsulated with the
concrete to form the central core of the blocks. Figure 2.1 shows the core of the block
made by the compression of tires. It is designed with an external interlocking system to
enhance stmctural wall strength and to simplify and reduce the installation time. The
external interlocking design of Eco-Bloc'^^ is shown in Figure 2.2.
:^-<^^t\'%\'r«^j5^^ : < ^ '>• < s \
Figure 2.1: Compressed Tires (4)
Figure 2.2: Interlocking Design of Eco-Bloc™ (4)
7
2.2.2 Different Types of Eco-Bloc (4^
2.2.2.1 Bulkhead/Erosion Control
The bulkhead/erosion control Eco-Bloc™ dimensions are 4'x4'x8', weighs
approximately 5.5 tons, and has the equivalent stmctural integrity as a solid concrete
block. Figure 2.3 shows the oblique view of a 4'x4'x8' Eco-Bloc unit. The economic as
well as environmental advantage of building with the Eco-Bloc™ is that it contains 120
scrap tires (1 ton of waste material), which displaces approximately 52% of the concrete
cost. EBS makes the Eco-Bloc"^^ flexible as the size, shape and stmctural integrity to
meet project specifications and it can be manufactured at the constmction site. This
product can be used for building retaining walls.
2.2.2.2 Perimeter Wall
The tilt wall style Eco-Bloc^^ can be used for walls, barriers, security enclosures,
etc. It is 2'x8'x10' in size and can be installed in the horizontal or the vertical position.
EBS makes available over 30 standard architectural patterns for the exposed surface of the
block.
2.2.3 Design Criteria (5)
The Eco-Bloc"^^ design is based on the engineering concept of weight combined
with a tongue and groove system for lateral resistance. The tongue in the concrete block
provides automatic alignment of the blocks, which in most cases, eliminates the need for
mortar. Each segmental stmctural unit serves as a gravity stmctural element for walls,
stmctures, and a permanent erosion control unit. The basic unit has a minimum wall
thickness of 6 inches with a central core of recycled tires.
The overall design configurations include:
• Unit geometry,
• Loading,
• Location (dry/wet).
8
8"{typ)
6"(typrZ
I />•* 4'-0
4'-0
Figure 2.3: Oblique View of Eco-Bloc™ Unit (5)
Two units are available: a steel reinforced unit for stmctural applications and a
plain concrete unit for non-stmctural applications. The basic unit is manufactured using
3000-psi concrete and has a minimum wall thickness of 6 inches with a central core of
recycled tires.
Table 2.1 is presented to provide basic engineering data for a single containment
unit, meeting minimum reinforcing requirements of the American Concrete Institute
(ACI), ACI 318-89 (revised 1992) specifications. The use of this data will allow an
engineer to design a wall system for site-specific conditions. A qualified engineer should
review any proposed application to be certain that the actual site conditions and the
proposed dimensions meet with standard engineering practice.
Table 2.2 provides engineering data for a single containment unit consisting of
plain concrete. This unit shall not be used in stmctural applications.
2.2.3.1 Design of the Unit
Three alternative designs of Eco-Bloc™ are presented based on the use of 3000
psi concrete. Altematives one and two meet the minimum reinforcing requirements of the
American Concrete Institute (ACI), ACI 318-89 (revised 1992) specifications. These
altematives are suitable for stmctural applications and the engineering properties of a
single unit (for either alternative one or two) are given in Table 2.1. Figure 2.4 shows the
first alternative, which consists primarily of welded wire fabric reinforcing. The second
alternative, shown in Figure 2.5, consists of number three steel reinforcing bars. The third
alternative is a plain concrete unit with comer reinforcing only and it is shown in Figure
2.6. It does not meet ACI code requirements and is not applicable for stmctural
applications requiring code conformance. The engineering properties of this alternative
are given Table 2.2. This alternative may be subject to shrinkage and/or thermal induced
cracking.
10
Table 2.1: Engineering Properties of Single Unit-Steel Reinforced (5)
Property
Weight
Allowable Surcharge Capacity Allowable Punching Shear on Side Wall
6"X6" area 9"X9" area 12"X12" area Allowable Lateral Load Capacity of Tongue
Allowable Bending Capacity of Single Unit with Simply Supported Ends (uniform load)
Units
lbs
kips
lbs lbs lbs kips/ft
kips/ft
Value
13,900
200
9,000 11,900 14,900 19.0
18.8
Table 2.2: Engineering Properties of Single Unit-Plain Concrete (5)
Property
Weight
Allowable Surcharge Capacity Allowable Punching Shear on Side Wall
6"X6" area 9"X9" area 12"X12" area Allowable Lateral Load Capacity of Tongue
Allowable Bending Capacity of Single Unit with Simply Supported Ends (uniform load)
Units
lbs
kips
lbs lbs lbs kips/ft
kips/ft
Value
13,900
200
9,000 11,900 14,900 19.0
6.0
11
W4.3 wire or W6.5 wire (typ)
Use WWF 4x4 or WWF 6x6 -
- W6 X W4.3 W9 X W6.5
W6 wire or W9 wire (typ)
6 #3 bars x 7'-8" O corners
(typ.)
Figure 2.4: Eco-Bloc™ Reinforcing Using Welded Wire Fabric (5)
6"
—3" cover (typ.)
20 / 3 bars x 7*-6" & 10" spacing
Z.
10 ^3 bars x 3'-6" 9 1 0 spacing Near and Far
-10 #3 bars x 3'-6" @ 10" spacing Top and Bottom
Figure 2.5: Eco-Bloc™ Reinforcing Using No. 3 Rebar (5)
12
6"
I 3" cover (typ.)
— 6"
6 #3 bars x 7'-6"
Figure 2.6: Eco-Bloc™ Using Plain Concrete (5)
13
2.2.4 Different Applications of Eco-Bloc™
Eco-Blocs can be used in different Civil Engineering applications. Some of the
typical usage of Eco-Blocs are in erosion control, wetland reclamation, traffic diversion,
building dikes or dams, sound barriers, warehouses, retaining walls, equipment bams,
parking lot levelers, retaining walls for bulk material, river wing dams, border walls,
prison walls and energy efficient homes. Figure 2.7 shows a retaining wall and Figure 2.8
shows a river wing dam built using Eco-Bloc™ units.
2.2.5 Features and Benefits of Using Eco-Bloc™ in Retaining Walls
Following are some of the features of Eco-Bloc™ units, which have beneficial
effects on constructing retaining walls.
a. Standard block has a 32 square foot base, which allows it to act as a foundation
unit eliminating the need for extra foundations.
b. Eco-Bloc's interlocking system makes the installation simple and cost-effective.
This interlocking also resists lateral movement.
c. Each block contains about 1 ton of waste material, which recycles waste from
environment. This also reduces concrete cost by approximately half, which
significantly reduces the cost and weight of the block.
d. The blocks can be manufactured at/near construction site, which reduces
overhead, and transportation cost.
e. The blocks can easily be reinstalled at another job site, as these are portable,
f The simplicity in manufacturing and installation minimizes the need for
technically skilled manpower,
g. This program can establish a community resource conservation program.
14
Figure 2.7: Walls Using Eco-Bloc Units (4)
Figure 2.8: River Wing Dam Built Using Eco-Blocs (4)
15
2.2.6 Economics of Construction bv Eco-Bloc™
Each Eco-Bloc' M unit contains about 1 ton of waste material, which reduces
concrete cost by approximately half, which significantly reduces the cost and weight of
the block. Standard block has a 32 square foot base (4'x8'), which allows it to act as a
foundation unit eliminating the need for extra foundations. The blocks can be
manufactured at/near construction site, which reduces overhead, and transportation cost.
The production price of each Eco-Bloc unit is currently approximately US $ 175/unit (4).
2.3 En-Core Tire Bales in the Construction of Retaining Walls
2.3.1 The En-Core Tire Baler (6)
The En-Core baler is manufactured by ENCORE SYSTEMS, inc., headquartered
in Cohasset, Minnesota. The En-Core baler is a vertical down stroke portable baler which
compresses approximately 100 whole passenger and light truck tires into a block
measuring 30 " x 50 " x 60 ". The baler has a chamber of about 5'x4'x2.5' which needs to
be filled three to five times before enough tires are compressed to complete the bale. The
baling process is shown in Figures 2.10-2.12. It takes about 15 minutes to produce a bale
depending upon the speed of the hydraulic system and the type of supportive equipment
used. Average production is 400 tires per hour. The weight of the completed block is
approximately one ton. This is a volume reduction of 5 to 1. The bales are secured with 5
strands of 9-gauge wire. The wires are 12 feet long, 2300-pound tensile strength, made of
carbon steel, galvanized or stainless steel with a "Square Loc" connecting knot.
In some cases, the bales are painted or coated with soil, shot-crete, plastic, foam,
or rubber compounds. Coating the bales improves the aesthetics and creates a barrier to
extend the integrity of the wire almost indefinitely.
The baler and two men are capable of making from four to six bales an hour on a
steady basis. The completed bales are ejected automatically. The completed bales can be
handled with a forklift, front-end loader, logger's clam or grappler. According to the
manufacturers, because of the uniformity of the bales, they can be easily stacked.
16
Figure 2.9: Tires Being Loaded in the Baler (6)
17
Figure 2.10: Tires being Compressed in the Baler (6)
Figure 2.11: Finished Bale Being Ejected From the Baler (6)
18
2.3.2 Summary of Test Results on Tire Bale ^7)
Stork Twin City Testing Corporation in St. Paul, Minnesota performed a creep
test and a load deflection test on a tire bale submitted by the Encore Systems of Cohasset,
Minnesota. In the creep test, the average ultimate deflection after 72 hours was 8.06
inches under a load of 88,000 lb. In the load deflection test, the average ultimate
deflection was 11.45 inches under the maximum load of 338,850 lbs.
2.3.3 Benefits of Using Baled Whole Tires (6)
ENCORE SYSTEMS, inc. claims that the baler is relatively inexpensive, has
virtually no down time, and has very low maintenance costs.
Tires in baled form do not hold water; therefore, pose no threat to public health
due to mosquitoes. Because of the density of the bale, the decreased surface area, and
lack of air, the fire hazard is greatly reduced. The volume reduction of 5 to 1 makes the
storage and transportation of tires more convenient. The uniformity of the bales makes
them a feasible product to be used in Civil Engineering applications.
The comprehensive advantage to this method of scrap tire processing is the
potential use as an end product. Increasing disposal costs and state laws make the option
of baling whole tires an attractive and cost-effective alternative.
2.3.4 Costs of Baler. (6)
The operating and maintenance costs, as given by the ENCORE SYSTEMS, inc.
are given below:
1. Hvdraulic Maintenance Costs
Based on 48 H.P. Kubota diesel engine baling 1,000 bales @ 4 bales/hour
Assuming $10/hour labor costs, 1 hour labor @ $10.00/hour = $ 10.00
Filters/Parts — $ 27.85
Hydraulic Maintenance Costs To Bale 1,000 Bales = $ 37.65
19
2. Engine Maintenance (Kubota^ Costs
1 hour labor @ $10.00 per hour = $10.00
parts (filters, oil change) = $15.00
Engine Maintenance Costs = $ 35.00
3. Fuel Consumption Costs
48 H.P. Kubota diesel engine - 1.25 gallons/hour.
1,000 bales @ 4 bales per hour = 250 hours
@$1 .25/gallon = $ 250.00
4. Labor Costs
3 men @ $10.00/man per hour baling 1,000 bales in 250 hours = $ 7,500.00
5. Wire Costs
5 galvanized wires per bale
1,000 bales = 5,000 wires @ $.45/wire — $ 2,250.00
6. Total Cost to Bale 1000 Bales/100,000 Tires
= $10,072.65/$.10 per tire.
2.3.5 Different Applications of Baled Tires
Many successful projects have already been completed using the bales. Some of
these projects include impact barriers, erosion control, land reclamation, equine training
arenas, fences, and dam construction. Tire bales were used in erosion control projects like
that in Carlsbad, New Mexico; Manitou Springs, Colorado and Cohasset, Minnesota. Tire
bales have been used as Subgrade Lightweight Fill for Road Construction in Chautauqua
County, New York and also in Pueblo, Colorado. Figure 2.12 shows the bales being used
as Subgrade Lighwight Fill for Road construcfion. Entrance walls and Equipment
buildings have been built ufilizing the bales in Pueblo, Colorado. Over 5,000 bales have
been used to elevate 4 acres of soil for using as a parking lot. Over 50,000 bales have
been used to build a dam in Mountain Home, Arkansas. They were used as fill material
on both the upper and lower sides of the dam.
20
Figure 2.12: Tire Bales as Subgrade Lightweight Fill for Road Construcfion (6)
2.3.5.1 A Brief Description of Carlsbad, NM Project (6)
This project began in September of 1997, and used approximately 700,000
recycled scrap fires in the form of one-ton bales to stabilize 4,400 feet of the East bank of
the Pecos River in Lake Carlsbad.
Figure 2.13 shows the extent of erosion near the Carlsbad Country Club. The
erosion was being caused by wave action of pleasure watercraft. The river was drained to
allow for construction of the erosion control project.
The first step was to dig a three to four foot deep trench along the river's edge.
This was lined with a concrete foundation, and set with steel reinforcing bars. Then, one-
ton bales produced by Encore's Baler were set on top of the concrete and secured in
place. Figure 2.14 shows the bales on top of concrete foundation. The next step involved
encapsulating the tire bales in concrete. The encapsulation process is shown in Figure
2.15. The encasement in concrete enabled the tire bales to serve as a foundafion for a
concrete block wall, and prepared them for the application of a layer of facing stone,
which was laminated to the front of the bales. A block retaining wall was then
21
constructed on top of the bales and backfill was applied behind the wall. Figure 2.16
shows the block retaining wall on top of the bales.
Figure 2.13: Erosion in Lake Carlsbad (6)
22
Figure 2.14: Tire Bales on top of Concrete Foundafion (6)
Figure 2.15: Encapsulafion of Bales in Concrete (6)
23
Figure 2.16: Block Retaining Wall on Top of Bales (6)
24
CHAPTER in
STABILITY ANALYSIS AND DESIGN OF RETAINING WALL
3.1 Overview
From the research project's comprehensive literature review, two types of
retaining wall were chosen for further review and analysis. One was a Mechanically
Stabilized Earth retaining wall utilizing Eco-Bloc units and the other was Gravity
retaining wall using Encore Tire Bales. In the mechanically stabilized earth (MSE)
retaining wall, the earth mass is reinforced with a series of strips, which are attached to a
facing material. The facing resists the lateral thrust induced by the active earth pressure,
through the anchorage provided by the strips. The strips derive their tensile capacity fi-om
the friction developed between the strips and the earth. Figure 3.1 shows a typical MSE
wall construction using Eco-Bloc units. Gravity retaining walls depend solely on their
weight for stability. Different shapes of gravity retaining wall are shown in Figure 3.2.
This chapter presents detailed stability analysis for each type of wall.
3.2 Eco-Bloc Tire Retaining Walls
Eco-Blocs unit, patented by Ecological Building Systems, was used as the main
element to analyze and design mechanically stabilized earth retaining walls. The walls
were designed considering all possible modes of failure.
3.2.1 Modes of Failure
MSE walls shall be designed for external stability of the wall system as well as
intemal stability of the reinforced soil mass behind the facing. Both the external and
intemal stability failure problems were addressed in the design procedure.
25
Tire Containment
Unit
Surface Water Collection/Diversion
(optional) \
Drainage Tile (as Req'd)
''Leveling Pad
"" Foundation Soil
Groundwater Drainage System (if Req'd)
Figure 3.1: Typical MSE Wall Constmcfion using Eco-Bloc™ Units (5)
26
30"X50"X60"
6" concrete ' • = d 3 r
± 12" thick • concrete base
^ ^ 1 > ^ ( »( 1 Backfill \-; ^^Draimge 1 II 1 •^> Fill
__jz]aa 1 ^ ^ • a a a %
18'
• • • • • 1 /Drainage
^ •3^< „ M , ^ r »
— J o wiue concrete ba se
(a) Pyramid-Shaped Gravity wall
30"X50"X60"<--tire bale
C 6" concreie [ ] [
II II 11
- 1 II II II 11 II 11 II 11 II
^ ^
1 s -s%
Ai
^8K ^ ^ Drainage
* ^ Fill
Backfill 18'
^xCrainage ^ ^ Pipe ^
12" thick -concrete base
36' wide concrete base
(b) Front-Stepped Gravity wall
^ -
30"X50"X60",,;;--;^^ 1 tire bale ~~~ ^ f
6" concrete -'^^^^^^^^-—^
12" thick • concrete base
II 11 II II 11 II I II
1 11 II II
Backfill
1
M
\
1 1
i
^,,---Drainage * ^ Fill
^....-^rainage ^ ^ Pipe 1
36' wide cone
k
W
rete b
(c) Rear-Stepped Gravity wall
Figure 3.2: Gravity Walls of Different Shape
27
3.2.1.1 External Stability
Stability computations shall be made by assuming the reinforced soil mass and
facing to be a rigid body. The external stability of an earth wall depends on the ability of
the reinforced soil mass to withstand external loads, including the horizontal earth
pressure from the soil being retained behind the wall and loads applied to the top of the
wall, without failure by one of the failure mechanisms: (l)sliding of the reinforced
volume along the base of the wall or along any plane above the base, (2) overtuming
about the toe of the wall and (3) bearing capacity failure or loss of serviceability because
of excessive settlement of the foundation soil.
1. Sliding Failure: It represents the ability of the reinforced structure to overcome
the horizontal force of the soil immediately behind it. The sliding failure
mechanism is shown in Figure 3.3 (a). The factor of safety of an earth wall
against sliding is typically taken as 1.5.
2. Overtuming Failure: this model the ability of the stmcture to overcome the
overtuming moment created by the soil pressures acting behind it. Figure 3.3 (b)
shows the overtuming failure mechanism. Design engineers have generally
accepted that reinforced soil walls should have a factor of safety of at least 2.0
with respect to overtuming.
3. Bearing Capacity Failure: The bearing capacity of the foundation soil must be
checked to ensure that the vertical load exerted from the weight of the wall and
surcharge is not excessive. Figure 3.3 (c) is an example of bearing capacity
failure. The generally accepted minimum factor of safety against this type of
failure for reinforced soil walls is 2.0.
28
J J . . . /
(a) Sliding
i - •• • ' •
(b) Overtuming
iiJ ±.J^ ^ - ^
- » - - • I »^
• . ^ I i © Bearing Capacity (d) Global Failure
Figure 3.3: Extemal Stability Failure Mechanisms of MSE Retaining Walls
Source: Allan Block Design Manual
29
3.2.1.2 Intemal Stability
Intemal stability requires that the reinforced soil stmcture be coherent and self-
supporting under the action of its own weight and any extemally applied forces.
Reinforcement loads calculated for intemal stability design are dependent on the soil
reinforcement extensibility and material type. In general, inextensible reinforcements
consist of metallic strips, bar mats, or welded wire mats, whereas extensible
reinforcements consist of geotextiles or geogrids. Intemal stability failure modes include
soil reinforcement mpture and soil reinforcement pullout. For a reinforced soil stmcture
to be intemally stable, the reinforcements must be able to carry the tensile stresses
transferred to them by the soil without mpture . In addition, there must be sufficient bond
between the reinforcements and the soil in the resisting zone that reinforcements do not
pull out under the load that they are required to carry. The basis for the intemal design is
to evaluate the required spacing and lengths of reinforcements so as to satisfy the mpture
and pullout criteria. Intemal stability is determined by equating the tensile load applied to
the reinforcement to the allowable tension for reinforcement, the allowable tension being
govemed by reinforcement mpture and pullout. Figure 3.4 shows the failure mechanism
of a mechanically stabilized retaining wall due to lack of intemal stability.
The load in the reinforcement is determined at two critical locations, i.e., at the
zone of maximum stress and at the connection with the wall face, to assess the intemal
stability of the wall system. Potential for reinforcement mpture and pullout are evaluated
at the zone of maximum stress. The zone of maximum stress is assumed to be located at
the boundary between the acfive zone and resistant zone. Potential for reinforcement
mpture and pullout are also evaluated at the connecfion of the reinforcement to the wall
facing.
A very important addifional intemal design considerafion concems loss of
reinforcement durability over time. Reinforcement deteriorafion can result from
corrosion, creep, and chemical and biological attack of the different reinforcement
materials. Current practices in design to prevent failure as a result of reinforcement
deteriorafion include use of additional reinforcement cross secfion to allow for corrosion
30
(a) Breakage
i 4 . I * •
f | l 1 . - . . . • J
^^•*dada*da**ak
(b) Pullout
© Bulging
Figure 3.4: Intemal Stability Failure Mechanisms of MSE Retaining Walls
Source: Allan Block Design Manual
31
loss, epoxy coating of metallic reinforcements, protection of geotextiles from exposure to
ultraviolet light, and design at reduced stress levels to minimize creep in plastic grids and
geotextiles.
3.2.2 Stability Analysis and Design of Retaining Wall
The present concept of systematic analysis and design of reinforced earth
stmctures was developed by a French Engineer, H. Vidal (1966). The mechanically
stabilized earth (MSE) retaining wall uses the principle of introducing reinforcing into a
granular backfill via mechanical means such as metal strips and rods, geotextile strips and
sheets, or wire grids.
The three basic components of MSE retaining walls are:
1. Earth fill - usually granular material with less than 15% passing #200 sieve.
2. Reinforcement - strips or rods of metal, strips or sheets of geotextiles or wire
gridding fastened to the facing unit and extending into the backfill some
distance.
3. Facing unit - not necessary but used to maintain appearance and to avoid soil
erosion between reinforcements. It may be curved or flat metal plates or
precast concrete strips or plates. In our case, Eco-Bloc units serve as the
facing unit.
MSE walls derive their lateral resistance through the dead weight of the
reinforced soil mass behind the facing. The current design procedures for reinforced earth
retaining stmctures consider the intemal and extemal stability analyses separately. MSE
walls shall be dimensioned to ensure that the minimum factors of safety required for both
intemal and extemal stability are satisfied. Different wall dimensions were analyzed for
different loading condifions, soil backfill properties and different types of reinforcement.
Both inextensible (metallic strips) and extensible (geotextile and geogrid) types of
reinforcement were considered in the design procedure. Diversified soil backfill
properties (fricfion angle varying from 25° to 35°) were considered. Different site settings
(horizontal backslope and sloping backslope) were analyzed in the design. Dissimilar
loading conditions (surcharge and non-surcharge) were analyzed.
32
General Design Procedure for MSE Walls: The following general procedure was
followed for the design of MSE walls.
1. Establish wall profile and design loadings.
Establish wall profile from the grading plan of the wall site and verify the
following design assumpfions:
• The wall face is vertical or nearly vertical;
• The backfill is granular and free draining;
• The wall is constmcted over a firm foundafion or stabilized, improved soils;
• The live loads are vertical.
If any of the design assumpfions are not safisfied, the design method must be modified.
2. Determine the properties of backfill soil, foundafion soil and retained soil.
Well-graded and fi-ee-draining granular material should be used as backfill of
mechanically stabilized earth reinforced walls. The fHction angle, (|), of the soil can be
estimated conservatively by a soil engineer or determined by performing appropriate
direct shear or triaxial tests. Diversified fricfion angle ranging from 25° to 35°was
considered in the analysis. The unit weight, y, can be determined in a moisture density
test. Generally, the unit weight at 95% Standard Proctor relative compaction is specified.
A unit weight of 115 Ib/ft was assumed in the analysis of the wall. Obtain the shear
strength and allowable bearing capacity of the foundafion soil. Determine soil-tie fricfion
angle, ^u-
3. Establish design factors of safety.
Suggested values of safety factors used in the stability analysis are as follows:
I. Extemal Stability
a. Sliding, Fs>=l.5,
b. Overtuming, Fo>=2.0,
c. Bearing Capacity, Fb>=2.0.
n. Intemal Stability
a. Breakage Strength, FB>=2.5,
b. Pullout resistance, Fp>=2.5.
33
4. Determine preliminary wall dimensions.
Determine the height of the wall; H. Heights extending fi-om 4' to 16' were
analyzed for the mechanically stabilized earth retaining wall. The heights were
incremented at an interval of 4', since the depth of the Eco-Bloc units are 4'. The heights
for gravity retaining walls ranged from 3' to 18'. Their height interval was 3' as the depth
of the EnCore Bale is 3'. An embedment depth, D is usually required for reinforced earth
stmctures to avoid bearing failure of the foundafion soil. Embedment is also required
because of risk of local failure in the vicinity of the spacing, depth of frost and risk of
scour or erosion-induced local damage. In any case, an embedment depth of 0.1 H is
usually used, H being the height of the wall.
5. Select reinforcement type and strength.
Both inextensible (metallic strips) and extensible (geotextile and geogrid) types of
reinforcement were considered in the design procedure.
Metallic strips of 1.6 by 0.2 inch with an ultimate tensile strength of 36 ksi were
considered in the analysis. Both the geotextile and geogrid were assumed to have
allowable tensile capacity of 100 lb/inch (17.5 kN/m). This is a conservative value.
6. Determine actions of lateral earth pressure due to overburden pressure and live
loads.
Active Earth Pressure Coefficient,
K,= ^'"^f^^^ (3.1)
y sin(0 - o)sin(^ + p)
where
0= back face of the retaining wall, (0=0 for vertical back face of the wall),
(t)= angle of intemal friction of backfill soil,
5= fricfion angle between back face of the wall and soil backfill,
p= slope of backfill.
The parameters of the above equation are shown in Figure 3.5.
34
A ' K A X H
Figure 3.5: Coulomb's Active Earth Pressure (12)
Both sloping and non-sloping conditions were analyzed in the design procedure.
A typical, modest slope of 15° was analyzed to represent a sloping back slope.
For a non-sloping backfill, the above formula simplifies to the simplest form of
Rankine equation,
K^ = t an ' (45 -^ /2 ) (3.2)
7. Calculate horizontal tensile stress at each reinforcement level:
Maximum vertical pressure on nth layer, QV = Yz + q,
Maximum horizontal pressure on nth layer, CTH = Ka (ay),
where
y = unit weight of backfill,
z = depth of reinforcement,
Ka = active earth pressure coefficient,
q = surcharge.
A surcharge value of 500 Ib/ft spanning over 25 ft was analyzed in the design.
35
Maximum tensile stress at nth layer,
T= (active earth pressure at depth z) x (area of the wall to be supported by the tie)
=(crh) X (s vxs h) (3.3)
where
Gh= horizontal pressure on reinforcement,
Sv= vertical spacing between reinforcements,
Sh= horizontal spacing between reinforcements.
Figure 3.6 shows the schemafic tensile force lines for both inextensible and
extensible reinforcements.
For metallic strips, values of horizontal and vertical spacing were assumed.
For geotexfile or geogrid, the vertical spacing of fabric layers (Sy) is calculated fi-om:
S . = ^ (3.4)
where
Taii= allowable fabric long-term tensile force per unit width,
ah= total lateral earth pressure for the layer,
FB= factor of safety against mpture.
The design specifications assume that the wall facing combined with reinforced
backfill acts as a coherent unit to form a gravity retaining stmcture. The effect of
relatively large vertical spacing of reinforcement on this assumption is not well known,
and a vertical spacing greater than 0.8 m (31 inches) shall not be used without full scale
wall data (e.g., reinforcement loads and strains, and overall deflections) which supports
the acceptability of larger vertical spacing.
36
OJH.
^ • ^ A - j , C
w Mion ( ' / 4 - « / 2 )
t-m ' II I
P)
Figure 3.6: Tensile Forces in the Reinforcements and Schematic Maximum Tensile Force Lines: (b) inextensible reinforcements, (c) extensible reinforcements
Source: James K. Mitchell and Barry R. Christopher, "Design and Performance of Earth
Retaining Stmctures", North American Practice in Reinforced Soil Systems,
Geotechnical Special Publicafion No. 25, 1990.
37
8. Check intemal stability:
Reinforcement loads calculated for intemal stability design are dependent on the
soil reinforcement extensibility and material type. Maximum reinforcement load is
obtained by multiplying a lateral earth pressure coefficient by the vertical pressure at the
reinforcement, and applying the resulting lateral pressure to the tributary area for the
reinforcement. The applied load to the reinforcement shall be calculated on a load per
unit of wall width basis.
Check against reinforcement mpture for each layer n.
For metallic strips,
T<L„ = '-^ (3.5) FB
where
T= developed tensile force in the reinforcement,
Taii= allowable tensile stress of the reinforcing material,
Ts= ultimate tensile stress of the reinforcing material,
FB = Factor of Safety against mpture,
w = width of each tie,
t = thickness of each tie.
For geotexfiles or geogrids,
T<T^„~ (3-6)
where
RF= RFIDXRFCRXRFD,
Tall = long-term tensile strength required to prevent mpture,
Tuit = ulfimate tensile strength of the reinforcement,
RF = combined reducfion factor to account for potenfial long-term degradation
due to installation damage, creep, and chemical aging,
38
RFiD = strength reducfion factor to account for installation damage to the
reinforcement,
RFcR = strength reduction factor to prevent long term creep mpture of the
reinforcement,
RFD = strength reducfion factor to prevent mpture of the reinforcement due to
chemical and biological degradafion.
9. Determine length of reinforcements:
Total length of fies at any depth is L = L r + Lg (3.7)
where
L r = length within the Rankine /Coulomb failure zone,
Le = Effective length of reinforcements.
The effective length of ties along which the fricfional resistance is developed may be
conservatively taken as the length that extends beyond the limits of the Rankine active
failure zone.
At any depth z.
I , = ^ - ^ (3.8) ' tan(45 + ^/2)
where
h= height of wall,
z= depth of reinforcement,
([)= angle of intemal fiiction of backfill soil.
Check against reinforcement pullout for each layer n.
Pullout occurs when the reinforcement is pulled out of the soil by the intemal forces of
soil causing the wall to experience bulging or even worse, falling apart. Adequate length
of reinforcement prevents pullout. The reinforcement pullout resistance shall be checked
at each level against pullout failure for intemal stability. A factor of safety of about 2.5-3
is generally recommended for fies at all levels.
39
For a given factor of safety against reinforcement pullout, Ff
j ^ , W A (3 2>vcr„ tan^^
For sheets of geotexfile, the values of w and Sh are meaningless. So, the equafion becomes
Le = -If^^^^ (3.10) 2cr., tan kO
where
Fp = factor of safety against pullout,
aa= lateral earth pressure at depth z,
ay = vertical earth pressure at a depth z,
Sy = vertical spacing of reinforcement,
Sh = horizontal spacing of reinforcement,
w= width of reinforcing ties,
k(|)= soil-tie friction angle (can be conservatively assumed to be 2/3 of intemal
friction angle of backfill, (|)).
Find fabric wrapped embedment length for geotextile.
The length of fabric-wrapped embedment, Lo is calculated by dividing the lateral
pressure-induced tension in the fabric by the fricfion mobilized between the soil and
fabric over its overlap length. The required fabric overlap length is calculated from:
A(7^ tan(A: )
So, a minimum fabric embedment length of 3 ft should be used.
40
10. Check the extemal stability of the wall:
Check for overtuming, sliding and bearing capacity failure needs to be done to
ensure the extemal stability of the MSE wall,
i. Check for overtuming.
The factor of safety against overtuming is defined as the ratio of the sum of
stabilizing moment to the sum of overtuming moment. The moments are calculated by
taking moments about the toe of the footing.
Fo = Resisfing Moment, MR/Overtuming Moment, Mo
MR = (Weight of soil, Ws)x(distance of Ws from front face of wall)+
(Weight of block, W b)x(distance of W b from front face of wall)+
(Weight of surcharge q, Wq)x(distance of Wq from front face of wall) (3.12)
Mo = Total soil thmst, PaX distance of Pa from base of wall
= l/2KayH^xH/3+KaqHxH/2 (3.13)
ii. Check for Sliding.
The factor of safety against sliding is defined as the ratio of the sum of horizontal
resistance forces to the sum of horizontal disturbing forces.
Fs = Horizontal resisting forces/ Horizontal driving forces
= (Ws +W b +W q)(tan k,|,)/( 1 /2 Kay H^+KaqH) (3.14)
where k(|) = friction angle at geotextile-soil interface = 2/3 (|).
iii. Check for Bearing Capacity Failure.
Since allowable bearing capacity depends on site conditions and these walls may
be used in a variety of condifions, a conservative approach was followed to check against
bearing capacity failure. Allowable bearing capacity of 3000 Ib/ft was assumed in the
design. Actual bearing pressure coming to the base was then calculated. The maximum
pressure usually occurs beneath the toe. This value must not exceed the allowable bearing
capacity of the soil, otherwise setfiement or vertical yielding may occur. Factor of safety
against bearing capacity failure was then determined by dividing allowable bearing
capacity (3000 Ib/ft ) by the actual bearing pressure, hi some cases, the reinforcement
length had to be increased to safisfy this criterion. Equations 3.15 and 3.16 were used to
obtain the actual bearing pressure coming to the foundafion soil.
41
Eccentricity,e='-''''''''^'"'^^^''''<^'^^ (3.15) Ws + Wb-vqL
n • Ws + Wb + qL , . . ,, Bearing pressure,cr = — (3.16)
L-2e
3.3 Encore Tire Bale Retaining Walls
Encore tire bales, produced by Encore Systems, inc., were used as the building
block for analyzing constmcfion of gravity walls. Different wall dimensions were
analyzed for different loading conditions and different soil backfill properties.
3.3.1 Modes of Failure
A gravity wall is typically intemally stable. The failure mechanisms of a gravity
wall are the same as those for the extemal stability of a mechanically stabilized earth
retaining wall. For the purpose of checking extemal stability, a gravity wall is treated as a
rigid monolith (i.e., no intemal yielding or distortion).
3.3.2 Stability Analysis
The same principles applied to ensure the extemal stability of the MSE wall was
applied to check the extemal stability of the gravity wall.
42
CHAPTER IV
DESIGN CHARTS AND SPECIFICATIONS
4.1 Overview
This chapter presents details of design charts and constmction specifications of
the mechanically stabilized earth retaining walls and gravity retaining walls. The
development of design charts involved repeated analysis for different site condifions,
different loading conditions, different wall configurafions and different natural properties.
After all the design combinafions are put into design, the designs are combined to form
design charts. After the design charts are completed, constmcfion detailing needs to be
determined. These details should include the stacking arrangement of fire bales,
connecting tire bales together and placing and compacting the backfill.
4.2 Selection of Design Parameters
Different wall dimensions were analyzed for different loading conditions, soil
backfill properties and different types of reinforcement. Both inextensible (metallic
strips) and extensible (geotextile and geogrid) types of reinforcement were considered in
the design procedure. Reasonable values were assumed for their tensile strength. The soil
parameters were selected based on commonly used soil backfill materials. Ranges of soil
backfill properties (friction angle varying from 25° to 35°) were considered. Different site
settings (horizontal backslope and sloping backslope) were analyzed in the design.
Dissimilar loading conditions (surcharge and non-surcharge) were also analyzed.
4.2.1 Wall Configurafions
Two types of retaining walls were considered in the analyses. They are the
mechanically stabilized earth retaining wall and gravity retaining wall. One configuration
of mechanically stabilized earth retaining wall was analyzed with different kinds of
reinforcement. Three types of gravity retaining wall were reviewed. These are pyramid
shaped, front-stepped and rear-stepped. These configurations are shown in Figure 3.2.
43
4.2.2 Site and Loading Condifions
Each configuration of both the mechanically stabilized earth retaining wall and
gravity retaining wall was designed for different extemal environment. Both horizontal
and sloping backslope were examined in the design. A modest slope of 15° was used to
represent a sloping backslope. Dissimilar loading environments were analyzed in the
design. One was with surcharge and the other was without surcharge loading. The
surcharge loading considered in these analyses included a uniformly distributed load of
500 Ib/ft spanning over 25 ft into the backfill.
4.2.3 Earth Reinforcement Systems
With strip reinforcement methods, a coherent reinforced soil material is created
by the interaction of longitudinal, linear reinforcing strips and the soil backfill. The strips
are normally placed in horizontal planes between successive lifts of soil backfill. For
concrete panel facings, the reinforcement strips are made of mild galvanized steel, with a
cross-secfion of 1.6 by 0.2 inch or 2.4 by 0.2 inch (40 by 5 mm, or 60 by 5 mm) or of
high strength steel with a cross-secfion of 2.0 by 0.16 inch (50 by 4 mm). Metallic strips
of 1.6 by 0.2 inch with an ulfimate tensile strength of 36-kip/sq inch were considered in
the analysis. Their surface is ribbed to improve the apparent soil-reinforcement friction.
Grid reinforcement systems consist of metallic or polymeric tensile resistant
elements arranged in rectangular grids placed in horizontal planes in the backfill to resist
outward movement of the reinforced soil mass. Geogrid reinforcements are produced and
marketed under the trade name "Tensar" by Netlon Limited in the United States, United
Kingdom, and elsewhere. Tensar geogrids are manufactured from high strength grades of
high-density polyethylene or polypropylene using a stretching procedure. Geogrids
generally are of two types: (a) uniaxial geogrids and (b) biaxial geogrids. Moderate
strength geogrids suitable for design lives between 1 year and 120 years have tensile
capacity of 100 lb/inch (17.5 kN/m). Facings can be formed for geogrids by looping
reinforcements at the face or by attachment of the reinforcement grids to concrete panels.
Continuous sheets of geotexfiles laid down altemately with horizontal layers of
soil form a composite reinforced soil material with the mechanism of stress transfer
44
between soil and sheet reinforcement being predominantly fricfion. The majority of
geotexfile fabrics used in soil reinforcement are made of either polyester or
polypropylene fibers. Woven, nonwoven needle-punched, nonwoven heat-bonded, and
resin-bonded fabrics are available as well as materials made by other processes. Moderate
strength geotextiles suitable for design lives between 1 year and 120 years have tensile
capacity of 100 lb/inch (17.5 kN/m). The durability of geosynthefic reinforcements is
influenced by environmental factors such as fime, temperature, mechanical damage,
stress levels and chemical exposure. Facing elements are commonly constmcted by
wrapping the geotextile around the exposed soil at the face and covering the exposed
fabric by gunite, asphalt emulsion or concrete. Altematively, stmctural elements such as
concrete panels or gabions can be used. Connecfion between the geotexfile sheet and
stmctural wall elements can be provided by casfing the geotexfile into the concrete,
fricfion, nailing, overlapping or other bonding methods.
4.2.4 Soil Parameters
The soil parameters selected in the design procedure represent the range of backfill
soils that are commonly used in retaining wall constmction. The soil parameters that were
assumed are soil friction angle and unit weight of soil. Soil friction angles ranging from
25° to 35°were considered in the analysis. A moderate unit weight of 115 lb/ft for soil
backfill was assumed in the analysis of the wall.
4.3 Design Charts
The design charts provided herein fumish an accurate esfimate of reinforcement
spacing and lengths for different configurafions of the walls. To use the charts, one has to
verify that the site and loading condifions match the given site condifions of the chart.
The following secfions provide the design charts of retaining walls for soil friction angle
varying from 25° to 35°. These charts may be used in projects that match the site and
loading descripfions provided in the charts.
45
4.3.1 Design Charts for Eco-Bloc Retaining Walls
Tables 4.1 through 4.4 fumish design charts for mechanically stabilized earth
retaining wall ufilizing Eco-Bloc units. Tables 4.1 and 4.2 are the design charts for MSE
walls to be built with metal strips as the reinforcement. Table 4.1 can be used for MSE
walls with backfill soil fricfion angle varying from 25° to 30°. Table 4.2 corresponds to
MSE walls with backfill soil fricfion angle varying from 30° to 35°. Tables 4.3 and 4.4
are the design charts for MSE walls to be built with geotexfile / geogrid as the
reinforcement. Table 4.3 can be used for MSE walls with backfill soil fiiction angle
varying from 25° to 35°. Table 4.4 corresponds to MSE walls with backfill soil fricfion
angle varying from 30° to 35°. These tables provide the height and width of retaining
walls along with the lengths of reinforcement. The diagrams corresponding to the tables
are shown in Figures 4.1 through 4.6.
4.3.2 Design Charts for Encore Bale Retaining Walls
Tables 4.5 fumishes design chart for gravity retaining wall ufilizing Encore fire
bales as the building block. The table corresponds to a pyramid-shaped gravity retaining
wall or a front-stepped gravity retaining wall or a rear-stepped gravity retaining wall
(Figures 4.7- 4.9). The table can be used for soils with fricfion angle varying from 25° to
35°. The table corresponds to gravity walls with or without surcharge and also for both
horizontal and sloping backfill. The table provides the height and width of retaining walls
along with the number of bales and the number of rows of bales.
46
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Figure 4.1: MSE wall using metal strips with horizontal backfill and no surcharge
49
500 Ib/ft surcharge for 25'
2' r
B=l' embedme • i
&
Ll L2
i>" J^ 0 H=4' high MSE retaining wall
2.5'
2.5'
T
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i i
Ll ^
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H=8' high MSE retaining wall
2.5' vertical spacing
B=2' embedment
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Ll
I L2
5
L3
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H=12' high MSE retaining wall
2.5' vertical spacing
2' vertical spacing
B= 2' embedment
i00 Ib/ft surcharge for 25',
' . Ll ISL I
I L2 /
tft-
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L4
1 ^ . L5
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Figure 4.2: MSE wall using metal strips with horizontal backfill and 500 Ib/ft surcharge
50
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15° slope
2.5' vertical spacing
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2.5' vertical spacing
2' vertical spacing
15 slope
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Figure 4.3: MSE wall using metal strips with 15' sloping backfill and no surcharge
51
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2'
r B=r embedmei § 6 '
H=4' high MSE retaining wall
Spacing @ 2'
_L1
B=r embedment
1 ^ .
5: . iS i -
1 ^
^
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• ^
Dram Pipe
H=12' high MSE retaining wall
H=8' high MSE retaining wall
Drainage Fill
Spacing between Ll and L2 @2'
Spacing between L3 and L4 @1.5'
Spacing between L5 to L9 @r
Spacing between LIO to [email protected]'
B=2' embedment
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t • • I I 5
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a H=16' high MSE retaining wall
Figure 4.4: MSE wall using geosynthefics with horizontal backfill and no surcharge
54
2'
T B=l' embedme
500 Ib/ft surcharge for 25'
t3^ a Spacing @ 2'
H=4' high MSE retaining wall Spacing® r
B= r embedment
500 Ib/ft surcharge for 25'
5 / ^
Ci. Id".
I i?
Spacing
Spacing
@2'
500 Ib/ft surcharge for 25'
@1'
1^ Drainage Fill
I i •J".
^ ^.s^
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vf
\ ^
••A
Drain Pipe
H=12' high MSE retaining wall
Spacing between Ll and L2 @2'
Spacing between L3 to LIO @r
Spacing between Ll 1 to [email protected]' J
& ' .0' H=8' high MSE retaining wall
Drainage Fill
500 Ib/ft surcharge for 25'
l i i i i U i
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' ^
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if.
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f.
^ L ^
3?
0 B= 2' embedment
H= 16' high MSE retaining wall ^
Figure 4.5: MSE wall usmg geosynthetics with horizontal backfill and 500 lb/ft
surcharge
55
2' _LL
B=l'embedment
15° slope
' 5
H=4' highMSEretaining wall 0- Spacing @ 2'
r b=r ernbedment
: ^
^' >r
-M^
•0 H=8' high MSE retaining wall
-vv' Drainage Fill
B=2' embedment
Drain Pipe
H=12' high MSE retaining wall
Spacing between Ll and L3 @2'
Spacing between L4 to L9 @r
Spacing between LIO to [email protected]'
M
i.-tf
B= 2' embedment
t
15° slope
# ys^
#
^ '
A» ^
• A
..^"
H=16' high retaining wall
Figure 4.6: MSE wall using geosynthetics with 15° sloping backfill and no surcharge
56
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57
30"X50"X60" tire bale
6" concrete
Horizontal Backfill with
1 no surcharge
12" thick concrete base
Drainage Fill
H=18'
Drainage Pipe
B=36' wide concrete base
(a) Pyramid-Shaped Gravity wall
CZIT 30"X50"X60" tire bale
•a Dan
6" concrete
12" thick -concrete base
•aaa aaaaaI laaiaaarS
Drainage Fill
Horizontal backfill with no surcharge
Drainage Pipe
H=18'
B=36' wide concrete base
(b) Front-Stepped Gravity wall
30"X50"X60" tire bale
^ ^
1 ac
6" concrete
12" thick concrete base'
a Horizontal backfill with no surcharge
Drainage Fll
B=36' wide concrete base
(c) Rear-Stepped Gravity wall
Figure 4.7: Gravity Walls of Different Shape with no Surcharge
58
30"X50"X60" tire bale
6" concrete
12" thick concrete base
, 500 Ib/ft surcharge for 25'
I II 1 rJ ^ ^ D h i n a g e 1 II I 'if^ Fill
I 11 ] I I Horizontal ^ - — ^ ' — " - — - * backfill with 500
I ) ( Z Z ) I Z Z ) ( Z Z ] ^^^^' surcharge
aaaaa I i rnai~ir~i k
(a) Pyramid-Shaped Gravity wall
H=18'
I "rainage Fipe
B=36' wide concrete base
30"X50"X60" tire bale
6" concrete
12" thick -concrete base
30"X50"X60" tire bale
6" concrete
12" thick -concrete base
500 Ih/ft surcharge for 25'
aaac I
Horizontal backfill with 500 Ib/ft surcharge
Drainage Fill
Drainage Pipe
H=18'
(b) Front-Stepped Gravity wall
B=36' wide concrete base
500 Ib/ft surcharge for 25'
Horizontal backfil with 500 Ib/ft surcharge
I
1 Drainage Fill
Drainaj ;e Pipe
H=18'
(c) Rear-Stepped Gravity wall
B=36' wide concrete base
Figure 4.8: Gravity Walls of Different Shape with 500 Ib/ft Surcharge
59
30"X50"X60" tire bale
15° slope
•iT.
6" concrete
^ 15 sloping JI I backfill with
- ( >. no surcharge I
12" thick concrete base
nage
H=18'
Drainage pe
(a) Pyramid-Shaped Gravity wall
B=36' wide concrete base
15° slope
30"X50"X60"<-tire bale
L 6" concreie i [
^ — ' ^ — ar 12" thick ^ concrete base
)l
11
- 1 II II II II II II II II II
—' 15° sloping ty^ 1 backfill with no [i.
surcharge r
J %
^ ^
•^ h>—-5o wide concrete base
. Drai nage Fill
H=
Drai nage Pipe^
(b) Front-Stepped Gravity wall
30"X50"X60' tire bale
6" concrete
12" thick -concrete base
15° slope
15° sloping backfill with no surcharge
Da inn
(c) Rear-Stepped Gravity wall
Drainage Fill
Drainagt Pipe
H=18'
B=36' wide concrete base
Figure 4.9: Gravity walls of Different Shape with 15' Sloping Backfill
60
4.4 Construction Costs of the Tire Retaining Walls
The total cost of earth retaining walls is composed of materials, construction and
backfill soil costs, and any special project features. Special project features might include
a special wall facing treatment or restricted site access. Usually, a reinforced retaining
structure may be 20 to50 percent less expensive than conventional altematives. This is
because the materials cost less, and the simple construction procedures result in lower
installation costs. An earth-reinforced wall may be especially cost effective where its use
permits the use of on-site soil as backfill material. The primary advantage gained from
the use of reinforced soil may be the improved idealization, which the concept permits;
thus structural forms that normally would have been difficult become feasible.
Reinforced soil structures will not always prove economical when compared with other
structural forms, but in many conventional situations where circumstances are favorable,
savings in cost may be realized. Cost comparisons are more difficult for slope and
embankment reinforcement because each situation is likely to be unique, and there may
be several options for each situation.
The derivation of cost estimates for a project is one of the significant elements in
the project. The total cost of a reinforced soil structure is made up of the following cost
estimates:
i. Excavation,
ii. Backfill,
iii. Reinforcing connection elements and their installation,
iv. Facing elements,
V. Labor for transport and construction,
vi. Transport of materials,
vii. Drainage construction.
The above elements are interrelated and the minimum total cost of a structure may be
produced by a combination of the most compatible elements in any particular situation.
Accurate expense for the retaining walls could not be estimated as no retaining
walls of these types have ever been built. However, both the MSE wall and gravity
61
retaining wall should cost less than their conventional altematives because of lower
material cost.
The cost of excavation is less in the case of MSE walls built with Eco-Bloc units,
as they do not need any extra foundation. Standard block has a 32 square foot base
(4'x8'), which allows it to act as a foundation unit eliminating the need for extra
foundations. Gravity retaining walls made of Encore Tire Bales require concrete
foundation, the thickness of which is equal to the height of wall in inches (e.g., 12" thick
concrete foundation for a 12' high wall). The cost of fill materials is dependent upon local
availability and haulage rates. Reinforcement materials have different properties and
costs vary. MSE walls built of Eco-Bloc units require less reinforcement because of the
magnitude of the blocks. Gravity retaining walls are more economical than MSE walls as
they do not require any reinforcements. Both the Eco-Bloc units and encore Tire Bales
can be manufactured at/near the construction site, which reduces overhead and
transportation cost. The cost of drainage construction should not vary much for different
types of retaining wall, with site conditions determining the cost of drainage.
The tire bales make the big economic distinction. Producing tire bales is a far
better economic alternative than paying for the disposal of scrap tires. Each Eco-Block
unit contains 120 scrap tires (about 1 ton of waste material), which displaces
approximately 52 percent of concrete. This reduces the cost and weight of the block to
about half Moreover, each Eco-Bloc removes 120 scrap tires form the environment,
which would otherwise have to be disposed off in a landfill paying for their disposal costs
also. The disposal costs of tires vary from state to state. However, on average, their
disposal cost is around $ 1-1.5 per tire. Consequently, each block saves the state
approximately $ 150 in disposal fees. The price for each Eco-Bloc unit is approximately
US $ 175/unit. Producing the same volume of concrete of an Eco-Bloc unit (4'x4'x8')
would cost about US $ 250. The Encore tire bales contain 100 scrap tires. According to
the manufacturers, the production price of each bale is about US $15. hi addition to this,
each tire bale saves the state approximately $ 125 in tire disposal fees. The size of each
bale is 30"x50"x60"(1.93 cubic yard). Consequently, each tire bale displaces about 1.93
cubic yard of concrete from a gravity retaining wall.
62
4.5 Construction Technignpc for Tire Ret.inin^ w.iic
The topography, drainage pattems, soil conditions and local building codes and
regulations have to be considered for the construction of retaining wall. Construction of
reinforced soil structures must be consistent with the assumed idealization and analysis.
Speed of construction is essential to achieve economy and is detemiined by the rate of
placing and compacting the fill. Economy may be achieved by the simplicity of the
construction technique. Care must be taken that building units and reinforcements are not
damaged during construction. The following several factors have to be considered for
constructing retaining wall using tire bales.
When installing walls more than 4 feet high, particularly with surcharge loads, a
qualified engineer should be consulted, as recommended by the manufacturer's of the
Eco-Bloc units.
Foundation soil should be examined by the engineer to ensure that the actual
foundation soil strength meets or exceeds the assumed design strength. Site preparation
consists of excavating the area where construction is to take place to the limits shown in
the plans. Foundation soil should be excavated to a depth recommended by a qualified
engineer. The excavation width at any depth should be equal to or exceed the length of
the reinforcement layer planned for that elevation. Foundation preparation includes
removal of unsuitable materials or regrading the bottom of the excavation. Unsuitable
foundation materials may need to be replaced with compacted backfill prior to
construction of the MSE wall.
The first course of the concrete blocks shall be placed on the prepared base (no
extra foundation is necessary). The tire containment unit should be checked for levelness
and alignment. Units should be placed end to end for frill length of the desired structure.
Alignment could be done by using a string line or any other technique that is approved by
the engineer. The top of the unit should be cleaned before installing the next one on top
of it. The second course of tire containment units should be positioned upon the preceding
one, straddling two lower units, and staggering the vertical joints (no mortar or
interlocking pins are required). It is important that the Eco-Bloc units are not damaged
63
during handling. The stability of the facing panels during the backfilling operation can be
ensured by temporary struds placed on the extemal side of the wall.
For building gravity walls made of Encore Tire Bales, extra foundation needs to
be built. The thickness of the concrete foundation should be equal to the height of the
wall in inches, with a minimum of 6 inches. The first course of the tire bales shall be
placed on the foundation. There should be a gap of 6 inches between tire bales in both
vertical and horizontal direction. The bales need to be tied to one another in some
fashion. They can be tied with # 3 rebars running both vertically and horizontally. The
front of the wall should be painted or coated with soil, shot-crete, plastic, foam, or rubber
compounds. Coating the bales improves the aesthetics and creates a barrier to extend the
integrity of the wire almost indefinitely.
A well draining granular soil should be used as backfill behind the wall. Organic
topsoil should not be used. Clay soils or similar material should not be used as fill.
Compaction of the fill in a reinforced soil structure is desirable as it has a beneficial
influence on behavior and increases the efficiency of the structure. Proper compaction of
the backfill soil is required to minimize subsequent settlements and to ensure good soil-
reinforcement stress transfer. Each fill layer must be leveled after compaction to ensure
that all the reinforcements are in contact with the soil over their enfire bottom surface.
This may require some manual filling and tamping, particularly near the connection of
the reinforcements to the facing and in zones of difficult access.
The reinforcements should be laid flat on the compacted backfill and fixed to the
fie-strips protruding from the panels. All the reinforcements should be bolted to the tie-
strips, and corrosive protecfion should be applied to the bolts. Care should be taken to
ensure that the reinforcing strips are properly aligned after dumping the backfill.
A typical geotexfile-reinforced wall is constructed by placing horizontal layers of
geotextile in an earth fill (backfill), with the front edge of each geotextile layer wrapped
around the overiying layer of backfill to forni the wall face. The geotextile should be
unrolled in the direction specified in the design (machine or cross-machine direction).
Backfill is progressively dumped and spread toward the wall face. During backfilling
operations, no construction equipment should be pennitted to roll directly over the
64
installed geotextile, and a minimum backfill thickness of 6 in. should be maintained
Reinforcement layers and backfill are placed altemately as the wall height increases.
Materials used in the construction of a geotextile-wrapped wall face may be asphalt,
gunite, structural material or soil. Placement of either asphalt or gunite is usually by
spraying in one or several coats directly onto the geotexfile-wrapped face.
Geogrid reinforcement should be laid directly on the surface of a layer of
compacted fill and covered with the next layer of fill. Care should be taken to control the
timing and rate of placing of fill material to ensure that grids are not damaged by
compaction of site vehicles. Vehicles should not travel directly on the exposed
reinforcement. Uniaxial grids-Tensar SR2 are generally adopted as the main
reinforcement. When positioning the grids, particular attenfion should be given to ensure
that they are placed in the correct direcfions. The reinforcement is generally laid
horizontally in continuous strips of the required length.
Proper drainage of retaining soil structures is essential. Accumulation of water in
the backfill soil could cause a reduction in the effective vertical stress between soil and
reinforcement that would lower the pullout capacity of the reinforcement, resulting in
wall movements. The drainage of each structure or condition should be considered
separately on its merits. Proper drainage construction will control the flow and volume of
water around the retaining wall, hi the case of walls where the backfill material is poorly
draining, it is necessary to collect and remove the water by providing drainage blanket at
the back and beneath the reinforced structure, as shown in Figures 4.1 though 4.9.
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CHAPTER V
CONCLUSIONS AND RECOMMENDATIONS
5.1 Conclusions
The tire rubber is a dense, durable and elastic material that does not undergo
natural decomposition easily. However, tires in baled fomi do not hold water; therefore,
pose no threat to public health due to mosquitoes. Because of the density of the bale, the
decreased surface area, and lack of air, the fire hazard is greatly reduced. Utilizing this
property, tire bales can be used in many applications whereas scrap tires pose a number
of environmental and monetary hazards, hicreasing disposal costs and state laws make
the option of baling whole tires an attractive and cost-effective altemative. The global
advantage to this method of scrap tire processing is the potential use of an unproductive
material that had to be dispose off to a landfill with some disposal costs. The project's
literature search reveals that the tire bales are a potential product for Civil Engineering
applications like erosion control, wetland reclamation, construction of dam, retaining
wall, etc. Each tire bale contains about 1 ton of waste material, which recycles waste
from environment. This also reduces concrete cost by approximately half, which
significantly reduces the cost and weight of the block. Mechanically stabilized earth and
gravity walls utilizing tire bales appear to be two practical solutions to the disposal
problem of scrap tires. Both of them appear to be cost-effective as well as environment-
fiiendly.
5.2 Recommendations
No test wall could be built because of lack of fiinds in the project. A test wall
needs to be built to complement the stability analysis. Both the mechanically stabilized
earth retaining wall and three types of gravity retaining wall need to be test-built before
their implementation. A frill-scale test should enable the constructability review,
economic analysis and environmental impact analysis to be done. Constructability review
addresses different issues such as material availability, speed of construction and other
aspects of construction. Economic analysis is necessary to find the actual cost of wall
66
construction in terms of life cycle costs. It can be anticipated that tires in baled form and
encapsulated in concrete should pose no threat to environment. Still an environmental
impact analysis needs to be done before their public use. The Eco-Bloc units should have
to have some connection mechanisms to connect the reinforcements because connection
mechanisms at every half-foot of the block was assumed in the design.
67
BIBLIOGRAPHY
1. Rubber Manufacturers Association homepage, http://wvm. rma.org.
2. Proximity and Ultimate Analysis of TDF Waste Recovery, Inc., Hazen Labs, 1997.
3- Efficiency Resuhs of Multi-Fuel Firinp ABB Combustion Engineering Services Inc., Waste Recovery Inc., 1993.
4. Ecological Building Systems homepage, http://www.comwerx.net/biz/ecobloc.
5. Avent, R, Richard and Alawaddy, Mohamed, Analysis and Design of Concrete Tire Containment Unit, Ecological Building Systems, April 1995.
6. Encore Systems, Inc. homepage, http://www.tirebaler.com.
7 Stork Twin City Testing Corporation, Project: MNDOT Test of Tire Bale, Project No:03066, Date: March 24, 2000.
8. 1997 Interim Revisions to the Standard Specifications for Highway Bridges, 16 ^ Edition, 1996, American Association of State Highway and Transportation Officials.
9. Reinforcement of Earth Slopes and Embankments, National Cooperative highway Research Program Report 290, Transportation Research Board, Washington, D.C., June 1987.
10. Design and Performance of Earth Retaining Structures, Geotechnical Special Publication No. 25, American Society of Civil Engineers, 1990.
11. Design Manual, Allan Block Retaining Wall Systems, http://www.allanblock.com.
12. Das, Braja M, Principles of Foundation Engineering, 3''* Edition, PWS Publishing Company, Boston, Massachusetts, 1995.
13. Bowles, Joseph E., Foundation Analysis and Design, 4'*' Edition, McGraw-Hill, Inc., 1988.
14. Day, Robert W.. Geotechnical and Foundation Engineering, McGraw-Hill, Inc., 1999.
15. Liu, Cheng and Evett, Jack B., Soils and Foundations, 4* Edition, Prentice Hall, Englewood Cliffs, New Jersey, 1990.
16. Jones, Colin J FP, Farth Reinforcement andjoijjtructures, Butterworths, Stoneham.
Massachusetts, 1985.
68
17. Koemer, R.B., Design with Geosynthetics, 2"^ Edition, Prentice Hall, Englewood Cliffs, New Jersey, 1990.
18. Whitlow, R., Basic Soil Mechanics, 3"* Edition, Longman Scientific and Technical. Chicago, 1995.
19. Cemica, John N., Geotechnical Engineering: Foundation Design, John Wiley & Sons, Inc., New York, 1995.
20. Brown, Robert Wade, Practical Foundation Engineering Handbook, McGraw-Hill, New York, 1996.
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