CEE 434GEOTECHNICAL DESIGN

FALL 2008

GRADING AND SITE IMPROVEMENT METHODS

PART I

OUTLINE

I. Introduction

II. Case Studies

III. Factors Affecting Compaction

IV. Fundamentals of Shallow

Compaction

V. Examples

I. Introduction

When considering a site for construction, a Geotechnical Engineer encounters:

Abandon

Adapt

Alter

From: Coduto, 1999

“... almost no significant engineered construction occurs without the movement of soil from one place to another!”

-Ed Monahan, 1994

Research Park Tech Center IV Construction Camera #1

UNCONTROLLED AND CONTROLLED FILLS CONT’D…

2V TO 1H

Source: Greenfield, 1992

Research Park Tech Center IV Construction Camera #1

II. CASE STUDIES

Compaction at a Highway Off-Ramp

The next series of photos are from the construction of a highway off-ramp in Davis, CA, in 1995. This relatively small earthwork job was performed with very few pieces of equipment (a

cat, water truck, grader, and the trucks that transported fill soils to the site).

http://cee.engr.ucdavis.edu/faculty/boulanger/geo_photo_album/GeoPhoto.html

This cat is equipped with a blade for shaping the roadway and sheepsfoot rollers for compacting the clayey soils. Fill materials were brought to the site by trucks that spread the materials out in roughly 6 to 8 inch thick layers. The cat spread the material out evenly and compacted it at the same time.

The water truck sprays the earth during compaction to condition the soil to near its optimum moisture content for compaction, and to control dust at the site.

The operators of the water truck and cat sequence their passes across the site. A grader was later used for final shaping of the roadway surface.

Compaction at Los Vaqueros Dam

These next series of photos are from Los Vaqueros dam, California, during construction in 1998. This large earthwork project involved numerous pieces of equipment and required a

high degree of engineering quality control.

http://cee.engr.ucdavis.edu/faculty/boulanger/geo_photo_album/GeoPhoto.html

View of the embankment from the upstream side, with almost 2/3 of the embankment completed. Notice the haul roads on the left abutment.

Backhoes carefully place large rocks (rip-rap) on the upstream face. The rocks are carefully packed together to protect the dam face from erosion.

The different colored soils correspond to the upstream shell (left side), core (darkest), filter, and drain zone (lightest), and downstream shell.

The core materials are being disked (left side) and compacted by sheepsfoot rollers.

A closer view of the disk that breaks the imported soil down into smaller clods for effective moisture conditioning and compaction.

The downstream filter and drain zones are the lighter-colored soils in the middle of this photo.

The imported soils are raked by this caterpillar blade to remove any oversize boulders or cobbles.

III. Factors Affecting Compaction

a) Soil Type

b) Moisture Content

c) Thickness of lift

d) Degree of compaction (intensity of pressure &

the coverage area)

e) Number of passes

Among the Questions to be Answered on These Two Projects:

• Why do we need to compact the soil in the first place?

• How much would the fill settle?

• What are the strength and permeability characteristics of the constructed dam? How much leakage through and under the dam?

• Where do we get the material from (borrow)?

• How do we compact the fill (lifts, equipment, etc)?

• How much water do we need to add to compact efficiently?

• How thick a layer of gravel and rock facing …?

• How fast could the fill be placed?

• What are the maximum allowable slopes?

• How much would the fill settle?

IV. Fundamentals of Shallow Compaction

Air

Water

Solids

Air

Water

Solids

Air

Water

Solids

Natural Condition Being Hauled In Compacted Fill

Excavation, Transportation, and Compaction Stages of Construction

Stage 1. Laboratory Compaction

What is compaction?

A simple ground improvement technique, where the soil is densified through external compactive effort.

+ water =

Compactive effort

From: N. Sivakugan

From: Monahan, 1994

Source: Das, 2002

PROCTOR TESTS

• Standard Proctor – historically regarded as non-

load-bearing (or light bldg loads, parking lots,

lightly secondary roads).

• Modified Proctor – load-bearing, “comparable to

that obtained with the heaviest rollers under

favorable working conditions.”

(Sowers, 1979)

Compaction Curve

Water content

Dry

den

sity

( d

)

optimum water content

d, max

Soil grains densely packed

- good strength and stiffness

- low permeability

From: N. Sivakugan

Source: Das, 2002

From: Monahan, 1994

Zero Air Void Curve

All compaction points should lie to the left of ZAV curve

- corresponds to 100% saturation

Water content

Dry

den

sity

( d

)

Zero air void curve (S=100%)

s

wsd wG

G

1 :Eq

S<100%

S>100% (impossible)

From: N. Sivakugan

Compaction Curves for Spectrum of Soil Types

ED Monahan, 1994

Stage 2. Field Compaction

SPECIFICATIONS

• Degree of Compaction

R(%) = CR (%)= [(d)field /(d)max-lab]x100%

• Typical Spec’s

(d)field = CR(%) x (d)max-lab

-K.L. Lee, 1971

Relative Compaction – Relative Density Relationships

From: Caterpillar, 1993

Smooth Wheel Rollers

• 100% coverage (under the wheels)

• Contact pressure = 45 to 55 psi

• Sandy & clayey soils

Pneumatic Rubber-Tired Rollers

• 4 to 6 (tires) in a row

• Contact pressure = 85 to 100 psi

• 70 to 80% coverage

• Sandy & clayey soils

Sheepsfoot Rollers

• Projection area = 4 to 13 in2

• Contact pressure = 200 to 1000 psi

• Clayey Soils

Vibratory Rollers

Vibration – by rotating off-centers weights

Handheld ones for limited access areas

Granular soils

From: D’Appolonia, et al. 1969

From: Greenfield & Shen

From: D’Appolonia, et al. 1969

Stage 3. Assessment

Sand Cone Method

• ASTM D-1556• Glass (or plastic) jar with

a metal cone• Ottawa sand (known wt. &

vol.)• Dig a hole – weigh the soil

and obtain w(%)• Fill the hole with sand• Determine the new wt. &

vol.• Eventually, d = (dry wt. of excavated

soil)/vol. of hole

Rubber Balloon Method

• ASTM D-2167

• Similar to above

• Vol. is measured

utilizing a rubber

balloon filled with water

Nuclear Method

• Emits gamma rays

• Detects how the gamma

rays travel thru soil

• Amounts of gamma rays

detected correlate with

the unit weight of soil

V. Examples