The Deep Patch Technique for Landslide Repair · technique for repairing landslides with geosynthetic reinforcement. The technique involves replacing sections of roadway lost due

Report No. CTI-UCD-2-94

The Deep Patch

Technique for

Landslide Repair

Bassam M. Helwany Colorado Transportation Institute 4201 East Arkansas Avenue Denver, CO 80222

Final Report October, 1994

in cooperation with the Irtment of Transportation ighway Administration

Technical Report Documentation Page

1. Report No. 2. Government Accession No.

CTI-UCD-2-94

4. Title and Subtitle

The Deep Patch Technique for Landslide Repair

7. Author(s)

Dr. M. Bassam Helwany

9. Performing Organization Name and Address

Colorado Transportation Institute

4201 East Arkansas Avenue

Denver, CO 80222

12. Sponsoring Agency Name and Address

Colorado Department of Transportation

4201 East Arkansas Avenue

Denver, CO 80222

15. SuppJementaIy Notes

3. Recipient's Catalog No.

S. Report Date

October, 1994

6. Performing Organization Code

8. Performing Organization Rpt.No.

10. Work Unit No. (TRAIS)

11. Contract or Grant No.

93-482

13. Type of Rpt. and Period Covered

Final Report

14. Sponsoring Agency Code

270.01

Prepared in Cooperation with the U.S. Department of Transportation and the U.S. Forest

Service

16. Abstract

This report describes the laboratory testing of the "USFS deep patch" technique and a cn modification of this technique for repairing landslides with geosynthetic reinforcement. The technique involves replacing sections of roadway lost due to landslides on top of a geosyntheticaUy-reinforced embankment. The cn modification involves replacing the reinforced slope with a geosynthetically-reinforced retaining wall with a truncated base. Both techniques rely on the cantilevering ability of the reinforced mass to limit the load on the foundation with a high slide potential.

The testing was done in a plane-strain device, (8 feet high, 16 feet long, and 3 feet wide) with a floor that can be lowered down to simulate the loss of support due to additional sliding of the foundation. Both road base fill and shredded tire till were tested.

The tests with road base showed that (1) both the USFS and CI'I repair reduced effectively the adverse effects of local landsliding on the highway pavement by preventing crack propagation; (2) the USFS repair increased the stability of the repaired slope, which was in progressive failure, by reducing the stresses exerted on it; and (3) the cn repair produced substantially greater stresses on its foundation due to the truncated base of the reinforced mass. These higher stress of the cn method will probably aggravate the stability of the slope which was in the state of progressive failure before repair. The en method, however, provides a wider base for pavement reconstruction. Tests with shredded tires found that excessive deformation makes them unsuitable for either repair technique.

17. Key Words

geosynthetic, landslide

reinforcement, shredded tires

19.5ecurity Classif. (report)

None

ZO.security Classif. (page)

None

i

18. Distribution Statement

No Restriction

21. No. of Pages 22. Price

118

11

PREFACE

This Research Project was sponsored by the Colorado Transportation

Institute (CTI). Professor Jonathan Wu from the University of Colorado at

Denver was the Principal Investigator. Mr. Robert Barrett, a physical

science researcher I scientist III from the Colorado Department of

Transportation (CDOT) and the geotechnical research manager of CTI, was

.the General Manager of this project. Mr. John B. Gilmore, the chief

geologist of CDOT, Mr. Shan-Tai Yeh, a senior geotechnical engineer at

CDOT, and Dr. Trevor Wang, a bridge design engineer at cnOT have all

been involved in making this project successful.

iii

tv

TABLB OF CONTENTS

LIST OF TABLES

LIST OF FIGURES

CHAPTER

1. INTRODUCTION ......................•..........•........... 1

2. THE UNITED STATES FOREST SERVICE DEEP PATCH TECHNI QUE. . . . . . . . . . . . . . . . . . . . . . . . • . . . . . . . . . . . . . . • . . . . . . . . 4

2.1 THE DEEP PATCH TEST APPARATUS ....................... 4

2.2 CONSTRUCTION AND LOADING SEQUENCE ................... 6

2.3 TEST MA.TERI.ALS ....•................................. 8

2.3.1 THE GEOSYNTHETIC REINFORCEMENT ...•........ 8

2.3.2 THE GRAVELLY SAND ...........•............ I0

2.4 INSTRUMENTATION ..................................•. 11

2.4.1 TWO-COMPONENT LOAD CELL ....•............. 1l

2.4.2 HIGH ELONGATION STRAIN GAGE •............. 14

2.4.3 LUBRICATED LATEX GRID SYSTEM ..........••• 15

2.4.4 DI.AL INDICATOR .............•...........•• 16

2.5 RESULTS AND DISCUSSION OF RESULTS ................•. 17

2.6 SUMMARY AND CONCLUDING REMARKS .........•.......••.. 19

3. THE CTI DEEP PATCH TECHNIQUE ............................ 21

3 . 1 INTRODUCTION ....................................... 21

3.2 CONSTRUCTION AND LOADING SEQUENCE .................. 22

3.3 TEST MA.TERI.ALS ..................................... 24

3.3.1 THE GEOSYNTHETIC REINFORCEMENT .........•. 24

v

3.3.2 THE GRAVELLY SAND ........................ 24

3.4 INSTRUMENTATION .................................... 24

3.5 RESULTS AND DISCUSSION OF RESULTS .................. 25

3.6 THE CTI DEEP PATCH TECHNIQUE IN SILVERTHORNE ....... 27

3.7 SUMMARY AND CONCLUDING REMARKS ..................... 28

4 . THE CTI DEEP PATCH TECHNIQUE WITH SHREDDED TIRE .. AS BACKFILL ......................................... ;. .... 29

4 . 1 INTRODUCTION ....................................... 29

4.2 CONSTRUCTION AND LOADING SEQUENCE ............•..... 30

4.3 TEST MATERIALS ..................................... 30

4.3.1 THE GEOSYNTHETIC REINFORCEMENT ........... 30

4.3.2 THE SHREDDED TIRE ........................ 31

4 . 4 INSTRUMENTATION .................................... 33

4.5 RESULTS AND DISCUSSION OF RESULTS .................. 34

4.6 SUMMARY AND CONCLUDING REMARKS ..................... 35

5. SUMMARY AND CONCLUSIONS ................................. 37

5.1 SUMMARY ................................................................................... 37

5.2 CONCLUSIONS ........................................ 39

vi

List o~ Tables

Table 2.1 Magnitude and Duration of Drop Increments ........... 7

Table 2.2 Some Properties of the Geosynthetic Reinforcement ... S

vii

viii

Figure 1.1

Figure 1.2

Figure 2.1

Figure 2.2

Figure 2.3

Figure 2.4

Figure 2.5

Figure 2.6

Figure 2.7

Figure 2.8

Figure 2.9

Figure 2.10

Figure 2.11

Figure 2.12

Figure 2.13(a)

Figure 2.13(b)

Figure 2.14

Figure 2.15

List o~ Figure.

Schematic Diagram of the USFS Deep Patch Technique ................................................................. 42

Schematic Diagram of the CTI Deep Patch Technique .......................................................................... 43

The Deep Patch Test Apparatus ................. 44

The Front Crank which Operates the Front Two Jacks ...........•............•.•.... 45

The Back Crank which Operates the Front Two Jacks ..•...•....•...•.•.•........... 46

The Moveable Part of the Bottom Panel at 11 inch-Drop ............................... 47

The Vibratory Plate Compactor ..............•.. 48

Schematic Diagram of the Uniaxial Load-Deformation Apparatus .•........•......... 49

The Uniaxial Load-Deformation Test ............ 50

Steel Mold for Epoxy Application on the Two Ends of the Geotextile Specimen .....•. 51

Assembly of Steel Mold for Epoxy Application on the Two Ends of the Geotextile Specimen ....•..•..•...........•.... 52

Load-Deformation Behavior of the Geotextile Reinforcement ....••.......•........ 53

Grain Size Distribution Curve of the Gravelly Sand ............................. 54

Compaction Curve of the Gravelly Sand ......... 55

Triaxial Compression Test Results for the Gravelly Sand ............................. 56

Triaxial Compression Test Results for the Gravelly Sand ............................. 57

Instrumentation of the USFS Deep Patch Test ... 58

Schematic Diagram of the Two-Component Load Cell ................ .. .................... 59

ix

Figure 2.16

Figure 2.17

Figure 2.18

Figure 2.19

Figure 2.20

Figure 2.21

Figure 2.22

Figure 2.23

Figure 2.24

Figure 2.25

Figure 2.26

Figure 2.27

Figure 2.28

Figure 2.29

Figure 2.30

Figure 2.31

Figure 2.32

Figure 2.33

Figure 2.34

Instrumentation of the Two-Component Load Cell ..................................... 60

Steel Box for Load Cell Protection .•....•..•.. 61

The Load Cell Inside the Protective Steel Box .................................................................................... 62

Normal Stress Calibration of Load Cell .......• 63

Normal Stress Calibration Curves for Load Cell .............•......................•..... 64

Shear Stress Calibration of Load Cell ......... 65

Shear Stress Calibration Curves for Load Cell .......................................................................... 66

In-Soil Calibration of Load Cell .•............ 67

Strain Gage Mounting Method .......•............ 68

Strain Gage Covered with Protective Mixture . . . 69

Strain Gage Calibration in the Uniaxial Load-Deformation Test ..............••••.••.... 70

Calibration Curve for Strain Gage .......•..... 71

Environmental and Mechanical Protection of Strain Gages Using a Layer of Neoprene Rubber ................................................................................ 72

Geotextile Layer Instrumented with Strain Gages .................................................................................. 73

Lubricated Side-Wall Grid System (close-up) ... 74

Lubricated Side-Wall Grid System •..••...•..... 75

Displacement Field of the Backfill in the Unreinforced USFS Deep Patch Test .........•..... 76

The Crack Corresponding to 11 inch-Drop in the Unreinforced USFS Deep Patch Test ......... 77

Displacement Field of the Backfill in the Reinforced USFS Deep Patch Test ............... 78

Figure 2.35(a) Comparison of Crack Propagation in the Two Tests at 2 inch-Drop .......................... 79

Figure 2.35(b) Comparison of Crack Propagation in the Two Tests at 5 inch-Drop .......................... 80

x

Figure 2.35(c) Comparison of Crack Propagation in the Two Tests at 8 inch-Drop .......................... 81

Figure 2.35(d) Comparison of Crack Propagation in the Two

Figure 2.36

Figure 2.37

Figure 2.38

Tests at 11 inch-Drop .........•.........•....• 82

Comparison of Crack Propagation in the Two Tests ............................................................ 83

Distribution of Normal Stresses along the Bottom Panel in the Unreinforced USFS Deep Patch Test ...............•.................... 84

Distribution of Normal Stresses along the Bottom Panel in the Reinforced USFS Deep Patch Test .••.......•....•.......•.•.......••• 85

Figure 2.39(a) Distribution of Strain along the Geosyn-thetic Reinforcement Layer 1 in the Reinforced USFS Deep Patch Test ..........•.........••.... 86

Figure 2.39(b) Distribution of Strain along the Geosyn-thetic Reinforcement Layer 3 in the Reinforced USFS Deep Patch Test ......•.•......••......... 87

Figure 2.39(c) Distribution of Strain along the Geosyn-

Figure 3.1

Figure 3.2

Figure 3.3

Figure 3.4

Figure 3.5

Figure 3.6

Figure 3.7(a)

Figu~e 3.7(b)

thetic Reinforcement Layer 5 in the Reinforced USFS Deep Patch Test .....................•.... 88

Schematic Diagram of the CTI Deep Patch Test .• 89

The CTI Deep Patch Test at End of Construc-tion ........................................................... 90

Instrumentation of the CTI Deep Patch Test .... 91

Displacement Field of the Backfill in the CTI Deep Patch Test with Road Base Backfill ... 92

The Deformed Face of the CTI Deep Patch Test with Road Base Backfill after Removing the Berm ............................................................ 93

Distribution of Normal Stresses along the Bottom Panel in the CTI Deep Patch Test with Road Base Backfill ............................ 94

Distribution of Strain along the Geosynthetic Reinforcement Layer 2 in the CTI Deep Patch Test with Road Base Backfill .................. 95

Distribution of Strain along the Geosynthetic Reinforcement Layer 2 in the CTI Deep Patch Test with Road Base Backfill •.........•....... 96

xi

Figure 3.7(c) Distribution of Strain along the Geosynthetic Reinforcement Layer 6 in the CTI Deep Patch Test with Road Base Backfill •........•••...•.• 97

Figure 3.8

Figure 3.9

Figure 3.10

Figure 3.11

Figure 4.1

Figure 4.2

Figure 4.3

Figure 4.4

Figure 4.5

Figure 4.6

Configuration of the CTI Deep Patch in Silverthorne .................................. 98

Construction Procedure of the CTI Deep Patch in Silverthorne ...........................•... 99

Construction of the CTI Deep Patch in Silverthorne ......................•.......... 100

Construction of the CTI Deep Patch in Silverthorne ..•..•....••..............•..•..• 101

Schematic Diagram of the One-Dimensional Compression Test for Shredded Tire •.......•.. l02

The Load History of the One-Dimensional Compression Test on Shredded Tire ....•. .. .... l03

Stress-Strain Behavior of the Shredded Tire under One-Dimensional Compression ....•...••.. l04

Creep Behavior of Shredded Tire under a Constant Stress of 6.3 psi (arithmetic) ••.... 105

Creep Behavior of Shredded Tire under a Constant Stress of 6.3 psi (semi-logarithmic) ..............................•.. 106

Displacement Field of the CTI Deep Patch Test with Shredded Tire Backfill •.••........• 107

xii

CHAPTER 1

INTRODUCTION

The United States Forest Service (USFS) is currently using a new method

for landslide repair named "the USFS deep patch technique". The USFS deep patch

technique involves the removal of the top portion (5-6 feet-high) of the small-scale

sliding slope under a highway pavement and rebuilding that portion with the use

of horizontal layers of geosynthetic inclusions.

The USFS deep patch technique is illustrated in Figure 1.1. Figure 1.1 (a)

depicts a cross-section of a typical highway in a mountain region. Part of the

natural slope, which consists of inherently strong soil, is cut to allow for the

highway. The loose soil from the cutis used to fill, without compaction, the lower

part of the slope to form an extension to the existing foundation.

Due to the seasonal increase of pore water pressure in the soil combined with

soil creep and other factors, the fill part of the highway foundation may develop

a local landslide causing undesirable settlement in the highway pavement as shown

1

in Figure 1.1(a). The upper portion of the local landslide is removed and rebuilt,

as shown in Figure 1.1 (b) , utilizing horizontal layers of geosynthetic

reinforcement.

This study was aimed at investigating the effectiveness of the USFS deep

patch technique in (1) reducing the adverse effects of local landslides on highway

pavement and (2) increasing the stability of the repaired slope by reducing applied

normal stresses exerted on top.· The investigation was accomplished by devising

a large-scale apparatus, as shown in Figure 1.1 ( c), in which the USFS deep patch

technique can be closely simulated. Two large-scale deep patch tests were con

ducted. The first test, termed "the USFS unreinforced test", used a compacted

backfill without geosynthetic reinforcement, whereas the second test, termed "the

USFS reinforced test", used the same soil for backfill as the USFS unreinforced

test along with five equally-spaced horizontal layers of geosynthetic reinforcement.

Another deep patch technique, evolved from the USFS deep patch technique,

was also investigated. This technique, named the CTI (Colorado Transportation

Institute) deep patch technique, was suggested by Professor Zhenghuan Liao from

Chongqing University (P. R. of China). In the CTI deep patch technique the top

portion (5-6 feet-high) of the small-scale sliding slope under a highway pavement

is removed and then rebuilt in the form of a geosynthetic-reinforced soil "retaining

2

wall" with a reversed angle as shown in Figure 1.2.

There are two advantages of using the CTI deep patch technique. The first

advantage is the tolerance of the CTI deep patch to any subsequent settlement of

the repaired slope. If there is a tendency of further settlement in the repaired

slope, the geosynthetic-reinforced portion of the CTI deep patch will separate from

the repaired slope causing no distress in the highway pavement. The second

advantage of using the CTI deep patch technique is its ability to widen the highway

of an average of 4 feet as shown in Figure 1.2. Two CTI deep patch tests were

conducted using two different backfill materials. Road base class 1 backfill was

used in the first CTI deep patch test. On the other hand, shredded tire backfill,

which weighs approximately 1/3 of the road base backfill, was used in the second

CTI deep patch test.

3

CHAPTER 2

THE UNITED STATES FOREST SERVICE DEEP PATCH TECHNIQUE

2.1 THE DEEP PATCH TEST APPARATUS

A plane strain apparatus, within which the deep patch tests were conducted,

was devised and constructed. The state of plane strain, as defined in engineering

mechanics, is the state which occurs in structures that are not free to expand in

the direction perpendicular to the plane of the applied loads. If the applied loads

lie in the x-z plane (x is horizontal and z is vertical), then the displacement in the

y-direction is zero.

The apparatus, shown in Figures 1.1 (c) and 2.1, measures 8 feet high, 16

feet deep and 3 feet wide. The apparatus has two side panels, one back panel, and

a bottom panel. The bottom panel consists of two parts: a stationary 7 feet-long

part and a moveable 9 feet-long part. The moveable part is held:in place by four

jacks at its four corners as shown in Figure 2.1. The front two jacks can be

lowered simultaneously by the use of one crank. shown in Figure 2.2. The back two

4

jacks can also be lowered simultaneously by the use of another crank shown in

Figure 2 . 3. This arrangement allows the moveable panel to be lowered at the front

and at the back simultaneously in a uniform motion. Moreover, this arrangement

allows the moveable panel to be lowered at an angle. The 'moveable part can be

vertically lowered in a uniform manner about 1 foot. Figure 2.4 shows the moveable

panel at 1 foot drop.

~he side panels were constructed with 0 . 5 inch -thick transparent plexiglass

as shown in Figure 2.1. The back panel was made of a 0.75 inch-thick plywood.

The bottom of the testing apparatus was a rough surface created by gluing coarse

aggregate to its steel plate floor. The treated surface was covered with a 2 inch

thick layer of Ottawa sand before placing the first layer of geosynthetic sheet.

The side and back panels were heavily reinforced with 0.2 inch thick, 4.0 inches

by 2.0 inches rectangular steel tubing with center-to-center spacing of 2 feet

horizontal and 2 feet vertical. After the backfill was emplaced, the moveable part

of the bottom panel was gradually lowered to simulate progressive local landslide

such as the one shown in Figure 1.l(a) .

To insure plane strain condition for the deep patch backfill throughout the

test, the following three measures were taken:

(a) The test apparatus was made very rigid. The lateral deformation of the side

5

walls will be'negligible.

(b) The adhesion between the backfill and the side panel was minimized so that

the shear stress induced on the side walls became negligible. This was

accomplished by creating a lubrication layer between the side wall and

backfill. The lubrication layer consists of a 0.02 mm thick latex membrane

and a thin layer of silicone grease. This procedure has been used

extensively by Tatsuoka at the University of Tokyo and Wu at the University

of Colorado at Denver. The friction angle between the lubrication layer and

p1exig1ass as determined by direct shear test is less than one (1) degree

(Tatsuoka, et aI., 1984).

(c) The backfill was very uniform across the width of the deep patch test so that

there was practically no variations in terms of the geometry and the material

along the width of the wall.

2.2 CONSTRUCTION AND LOADING SEQUENCE

- Road base (class 1) backfill was placed in 6 inch -thick lifts to construct a 1 : 1 • 25

slope. Each lift was uniformly compacted using a vibratory plate compactor,

shown in Figure 2.5, in a consistent pattern. The relative compaction of the

backfill soil was approximately 98%. Upon completing the placement of two layers

6

of soil (12 inches-thick), a sheet of geosynthetic reinforcement was placed

horizontally.

- Upon reaching the full height of 6 feet, three 6 inch-thick layers of the same

backfill material, without reinforcement, were placed and compacted on the top

surface of the backfill as surcharge.

- Ten uniform drop increments of the moveable part of the bottom panel were

performed at a rate of 1 inch/minute. A waiting period followed each increment

to allow for taking measurements. Table 2.1 gives the magnitude and the

duration (drop time + waiting period) of each increment.

Table 2.1 Magnitude and Duration of Drop Increments

Increment Magnitude Duration (inches) (minutes)

1 0.2 5 2 0.2 5 3 0.2 5 4 0.4 20 5 0.5 ·5 6 0.5 20 7 1.0 20 8 2.0 20 9 3.0 20 10 3.0 20

7

2.3 TEST MATERIALS

2.3.1 THE GEOSYNTHETIC REINFORCEMENT

The reinforcement used in the tests was a nonwoven heat-bonded polypropylene

geotextile. Some of its index properties provided by the manufacturer are

presented in Table 2.2.

Table 2.2 Some Properties of the Geosynthetic Reinforcement

Unit weight (ASTM D-3776) Grab tensile (ASTM D-4632) Elongation at break. (ASTM D-4632) Modulus at 10% elongation (ASTM D-4632) A.D.S. (ASTM D-4751) Permittivity (ASTM D-4491) Coefficient of permeability Nominal thickness

60 %

1.93 N/m2 890 N

4.45 KN 0.101 mm

O.l/sec 1.99x10-4 cm/sec 0.508 mm

To evaluate the load-extension behavior of the geosynthetic reinforcement a

uniaxial load -deformation apparatus was devised and constructed. The apparatus,

schematically shown in Figure 2.6, consists of two steel clamps which can be rigidly

attached to the jaws of a MTS-810 machine as shown in Figure 2.7. The clamps

were set to accommodate a 30 cm (1 ft)-wide and 2.54 cm (1 inch)-long geotextile

sample (the aspect ratio of 12 to suppress "necking" of the geotextile sample). To

insure uniform straining, the geotextile sample was reinforced at its top and bottom

8

with a 0.6 cm (0.25 inch) -thick layer of high strength epoxy as shown in Figure

2.6.

To insure test accuracy and repeatability, the uniaxial load -deformation

apparatus was designed and constructed carefully taking the following measures

into consideration:

- The apparatus was made very rigid to avoid bending and rotation.

- The two clamps were precisely made parallel to each other, i. e., the initial

distance between the clamps (equal to the length of the geotextile sample) can

be preset, for example, to a uniform distance of 2.54 cm (1 inch).

- The geotextile sample was reinforced with a thick layer of high strength epoxy

at its top and bottom. A precision -made steel mold, shown in Figures 2.8 and

2.9, was used for that purpose.

Numerous load -deformation tests were performed on identical geotextile samples

under identical conditions. The repeatability of the test was excellent even under

different loading conditions such as uniaxial tension under constant strain rate,

creep, relaxation, and recovery (Helwany and Wu, 1994).

The uniaxial load-deformation behavior of the geotextile used in all deep patch

tests, tested at a constant strain rate of 1% per minute, is shown in Figure 2.10.

9

The results shown in the Figure were obtained by testing a geotextile specimen of

30 cm (12 inches) in width and 2.54 cm (1 inch) in gage length. The test was

performed without pressure confinement on the geotextile specimen. Previous tests

?f this geotextile have indicated that the load -extension behavior of the geotextile

is not affected by confining pressure up to about 300 KPa (Wu, 1991).

2.3.2 THE GRAVELLY SAND

The soil used in the gravelly sand backfill test was a brown gravelly sand

classified as A-1-B (Road Base class 1) with the grain size distribution curve

s~own in Figure 2.11 (Cu=15. 7 and Cc=O. 77). The specific gravity of the soil was

2.63. The optimum water content of the soil was 10.2% and the maximum dry

density was 19.84 KN/m3 (126.3 pcf).

The compaction curve of the backfill soil is shown in Figure 2.12. The in-situ

water content of the backfill soil in all deep patch tests was approximately 8.5%.

The corresponding dry density was approximately 19.8 KN 1m3 (126.0 pcf) with a

relative compaction of approximately 99%.

Three CD triaxial compression tests were performed on the gravelly sand at

three confining pressures: 103 KPa, 207 KPa and 310 KPa (15 psi, 30 psi and 45

psi). The gravelly sand was compacted to achieve a dry density of approximately

10

•

19.8 KN/m3 (126.0 pcf) at 8.5% water content (similar to the in-situ condition in the

deep patch tests). The results of the CD tests are shown in Figure 2.13.

2.4 INSTRUMENTATION

All tests were instrumented to measure their behavior during construction and

upon dropping the moveable part of the bottom panel. A number of different

instruments were used to monitor the performance of the tests. They were two-

component load cell, high-elongation strain gage, lubricated latex grid and dial

indicator. Figure 2.14 illustrates the location of instrumentation in the USFS deep

patch tests. Instruments were read by a MEGADAC 2200C data acquistion system.

2.4.1 Two-Component Load Cell

Six two-component load cells capable of measuring normal and shear stresses at

the same point were installed along the bottom panel to monitor the stresses exerted

to it by the backfill. These load cells have been used successfully by Tatsuoka and

his colleagues at the University of Tokyo (Huang and Tatsuoka, 1990) and by Wu

(1992b). A unique feature of the load cell is that there is a very little coupling

between the forces registered in the two orthogonal directions, i. e. , there is very

little coupling between the normal and shear stresses.

11

A schematic diagram of the load cell is shown in Figure 2.15(a). In the figure,

the normal stress applied to the load cell will cause stress concentration at the top

(and bottom) of the horizontal cavities. On the other hand, the shear stress

applied to the load cell will caus,e stress concentration at the top (and bottom) of

the vertical cavities. Four strain gages arranged in full bridge configuration are

set in stress concentration regions resulting from the application of normal stress.

Another four strain gages arranged in full bridge configuration are set in stress

concentration regions resulting from the application of shear stress as shown in

Figure 2.15(a). The method of wiring the full bridge configuration is shown in

Figure 2.15(b). Figure 2.16 shows a fully-instrumented load cell.

The method of mounting the load cell on the bottom panel is shown in Figure

2.15(c). To insure realistic and accurate measurements of normal and shear

stresses exerted to the bottom panel by the backfill, the exposed surface of the

load cell has to be even with the inner surface of the bottom panel as shown in the

figure. The load cell was secured inside a 1. 25 cm (0.5 inch)-thick steel box,

shown in Figures 2.17 and 2.18, which was placed inside the bottom panel as shown

in Figure 2.15(c).

To calibrate the load cell for normal stress, the load cell was horizontally

positioned on a flat rigid surface and a vertical dead weight was applied to its top

12

surface in small in~rements as shown in Figure 2.19. The calibration curve of

normal stresses for load cells 1, 2, 3 and 4 is shown in Figure 2.20. It is noted

from the figure that the response of the load cell to applied normal stresses is

linear.

To calibrate the load cell for shear stress, the load cell was vertically positioned

on a flat rigid surface and a vertical dead weight was applied in small increments

in the shear direction (parallel to the top surface of the load cell), using a special

frame shown in Figure 2.21. The calibration curve of shear stresses for load cells

1, 2, 3 and 4 is shown in Figure 2. 22. It is noted from the figure that the response

of the load cell to applied shear stresses is linear.

The load cells were further calibrated for normal stresses using a different

method. In this method a 30 em-thick layer of Ottawa sand confined inside a

plexiglass cylinder was placed on top of the load cell. A dead weight was applied

to the top of the Ottawa sand as shown iIi Figure 2.23. The normal stress

calibration factor of the load cell obtained from this method was 10-20% less than the

normal stress calibration factor of the load cell obtained from the previously

described calibration method. This was attributed to soil arching. It is to be

noted that the adhesion between Ottawa sand and the inner surface of the

plexiglass cylinder was minimized so that the shear stress induced on the inner

13

surface of the cylinder became negligible. This was achieved by creating a

lubrication layer between the inner surface and the sand similar to the one used

earlier in the plane strain loading facility.

2.4.2 High Elongation Strain Gage

High elongation strain gages were mounted along the length of the geotextile

sheets to measure tensile strains induced in the geosynthetic reinforcement. The

mounting method suggested by Billiard and Wu (Billiard, 1989; Billiard and Wu,

1991) for strain gage on "extensible" materials was employed. In this method the

strain gage is glued to the geotextile sheet only at the two extremities of the gage

as shown in Figure 2.24.

The strain gages were covered with a protective mixture made of wax and

petroleum jelly as shown in Figure 2.25. This was necessary to protect strain

gages from soil moisture. This procedure has been successfully used by Helwany

(1993) in a fully saturated clay.

The wax and petroleum jelly protective mixture was very flexible yet nearly

impermeable. To evaluate this procedure, five strain gages were mounted on a 30.0

cm (12 inch) by 5.08 cm (2 inch) geotextile specimen and covered with the

protective mixture. The specimen was then strained using the uniaxial tension test

14

apparatus (described previously). The gage factor calculated from the calibration

curves was nearly identical to that calculated frorp. the curves' for strain gages

without the protective mixture. Figure 2.26 illustrates the uniaxial tension test for

strain gage calibration (without the protective mixture). The calibration curve of

the strain gages (without the protective mixture) is shown in Figure 2.27.

The mounting procedure of a strain gage on the geotextile sheet involves gluin.g

the two extremities of the strain gage to the geotextile using high strength epoxy

(5-ton clear epoxy). The epoxy is left to cure for at least 8 hours, thereafter: a

0.6 cm (0.25 inch) -thick layer of the protective mixture is used to cover the strain

gage and its terminal. Another 0.6 cm (0. 25 inch) -thick layer of the protective

mixture is used to cover the strain gage and its terminal from the opposite side of

the geotextile to provide complete protection against the moisture seeping through

the geotextile. For further environmental and mechanical protection a layer of

Neoprene rubber was used on top of the protective mixture as shown in Figure

2.28. Figure 2.29 shows a geotextile layer instrumented with five strain gages

being placed in the test apparatus.

2.4.3 Lubricated Latex Grid System

A lubricated latex grid system was established on the side wall to measure the

15

internal movement of the slope. The lubricated side-wall grid system has been

used successfully by Wu (1992b) to measure the internal movement of the backfill

in full-scale retaining walls such as the Denver Test Walls. The lubricated side

wall grid system consists of a 0.02 mm thick latex membrane and a thin layer of

silicone grease. A grid, with a vertical spacing of 7.5 cm (3 inch) and horizontal

spacing of 7.5 cm (3 inch) , was sketched on the latex membrane as shown in Figure

2.30. The friction angle between the lubrication layer and plexiglass as determined

by direct shear test is less than one (1) degree (Tatsuoka, et al., 1984),

therefore, the deformation of the lubricated side-wall grid will reflect very closely

the deformation of the backfill. Figure 2.31 illustrates the lubricated latex grid

system of the USFS deep patch test at the end of construction.

2 .4.4 Dial Indicator

Four dial indicators were used to measure the movement of the moveable part of

the bottom panel.

16

2.5 RESULTS AND DISCUSSION OF RESULTS

The displacement of the slope, the bottom panel, and the top surface in the USFS

unreinforced test, as measured by the lubricated latex grid, is shown in Figure

2.32. A near vertical crack emanating from a point on the slope nearly above the

inner end of the moveable part of the bottom panel is shown in the figure. The

crack started with the first drop of 0.2 inch and propagated throughout the test

due to further drops of the moveable part of the bottom panel. The depth of the

crack was approximately 70 inches and its width was approximately 12 inches due

to the 11 inch drop in the moveable part of the bottom panel (see Figure 2.33).

In contrast, the deformation behavior of the backfill in the USFS reinforced test

was much more favorable than the one in the USFS unreinforced test. Several small

cracks, shown in Figure 2.34, were detected in the beginning of the USFS

reinforced test, however, their propagation was very limited due to the soil

reinforcement. The deepest crack measured about 10 inches (deep) due to the 11

inch drop in the moveable part of the bottom panel. A detailed comparison of crack

propagation of the two tests for different drops of the moveable part of the bottom

panel is shown in Figure 2.35

A comparison between the crack in the USFS unreinforced test and the largest

17

crack in the USFS reinforced test is shown in Figure 2.36. The crack in the

unreinforced case was at least 8 times deeper than the one in the reinforced case.

The measured normal stress distribution in the USFS unreinforced test along the

bottom panel is depicted in Figure 2.37. It is to be noted from the figure that the

normal stress has substantially increased with the increase of drop of the moveable

part of the bottom panel in load cell #5 (located at 70 inches from the back panel,

close to the moveable part of the bottom panel). On the other hand, the normal

stress in load cell #4 (located at 97 inches from the back panel) decreased with

increasing the drop until the drop of 3 inches was reached. Thereafter, the normal

stress in load cell #4 drastically increased with increasing the drop. This is may

be attributed to the total separation of the backfill, due to the aforementioned

vertical crack, into two soil masses located above the moveable and the stationary

parts of the bottom panel.

The measured normal stress distribution in the USFS reinforced test along the

bottom panel is depicted in Figure 2.38. A substantial reduction in normal stress

is measured along the moveable part of the bottom panel as shown in the figure.

The sudden increase in normal stress in load cell #4, noted in the USFS

unreinforced test, is not encountere~ in the USFS reinforced test. Obviously, the

geosynthetic reinforcement was able to absorb the tension crack which occurred

18

in the USFS unreinforced test preventing the total separation of the soil into two

masses.

The measured strain distribution along the geosynthetic layers 1, 3 and 5 located

at elevations 1,3 and 5 feet are shown in Figures 2.39(a), 2.39(b), and 2.39(c),

respectively. The maximum strain of approximately 4%, corresponding to 8 inches

drop of the moveable part of the bottom panel, was observed nearly in the center

of the geosynthetic layer 1. Unfortunately, the three central strain gages in this

layer were lost after the 8 inch -drop due to excessive straining.

At 8 inch-drop, the maximum strain of approximately 2.4% was observed in the

geosynthetic layer 3. Again, the strain gage located at 115 inches from the back

panel was lost due to excessive straining when the drop exceeded 8 inches.

Relatively smaller strains were observed in the geosynthetic layer 5. The

maximum strain of approximately 1.0% was measured in the strain gage located at

72.7 inch from the back panel.

2.6 SUMMARY AND CONCLUDING REMARKS

To investigate the effectiveness of the .USFS deep patch technique for landslide

repair, a large-scale laboratory test apparatus was devised and constructed. Two

slopes, one unreinforced and one reinforced with geosynthetic inclusions, were

19

constructed inside the apparatus in plane strain condition. The moveable part of

the bottom panel of the apparatus was gradually dropped to simulate progressive

local landslide. The response of each slope to the drop was carefully monitored.

The tests results showed that the unreinforced slope suffered a severe distress

throughout the test. A large vertical crack initiated in the beginning of the USFS

unreinforced test and propagated throughout the test to the extent that the slope

was virtually separated into two parts. On the other hand, the reinforced slope

remained intact throughout the test with the exception of the few cracks initiated

in the beginning of the test but were suppressed by the geosynthetic

reinforcements.

The stresses exerted on the moveable part of the bottom panel in the USFS

reinforced test were substantially smaller than those in the USFS unreinforced

test. This reduction in stresses will enhance the stability of the slope which was

in the state of progressive failure before the USFS deep patch repair.

This investigation showed that (1) the USFS deep patch repair reduced

effectively the adverse effects of local landslides on highway pavement by

preventing crack propagation, and (2) the USFS deep patch increased the

stability of the repaired slope, which was in progressive failure, by reducing the

stresses exerted to it.

20

CHAPTER 3

THE CTI DEEP PATCH TECHNIQUE

3.1 INTRODUCTION

A new deep patch technique, evolved from the USFS deep patch technique, is

investigated in this Chapter. The new technique, named the CTI (Colorado

Transportation Institute) deep patch technique, was suggested by Professor

Zhenghuan Liao from Chongqing University (P. R. of China). In the CTI deep

patch technique the top portion (5-6 feet-high) of the small-scale sliding slope

under a highway pavement is removed and then rebuilt in the form of a

geosynthetic-reinforced soil "retaining wall" with a reversed angle as shown in

Figures 1. 2 and 3.1.


advantage is the tolerance of the geosynthetic-reinforced portion of the CTI deep

patch to any subsequent settlement of the repaired slope. If there is a tendency

of further settlement in the repaired slope, the geosynthetic-reinforced portion of

21

the CTI deep patch will separate from the repaired slope causing no distress in the

highway pavement. The second advantage of using the CTI deep patch technique

is its ability to widen the highway of an average of 4 feet as shown in Figure 1.2.

Two CTI deep patch tests were conducted using two different backfill materials.

Road base class 1 backfill was used in the first CTI deep patch test (described in

this Chapter). On the other hand, shredded tire backfill, which weighs

approximately 1/3 of the road base backfill, was used in the second CTI deep patch

test (described in Chapter 4).


- Road base (class 1) backfill was used (without compaction) to construct a 4 ft

high berm on top of the 3 inch-thick sand layer (which was placed on top of the

bottom panel) as shown in Figure 3.1. The front face of the berm has the slope

of 1 (vertical): 1 .25 (horizontal). The inner face of the berm has the slope of

2.25:1.

- A long sheet of geosynthetic reinforcement (long enough to wrap around the soil

layer, i.e., the length of the sheet =2 x length of the soil layer + the height of

the soil layer) was positioned on top of the 3 inch-thick sand layer. The excess

22

length of the sheet was positioned on top of the berm.

- Road base (class 1) backfill was placed on top of the geosynthetic reinforcement

in 6 inch-thick lifts to construct the geosynthetic-reinforced portion of the CTI

deep patch. Each lift was uniformly compacted using a vibratory plate compactor

in a consistent pattern. The relative compaction of the backfill soil was

approximately 98%. Upon completing the placement of two layers of soil (total

thickness of 12 inches), the excess length of the geosynthetic reinforcement

layer was wrapped around on top of the compacted soil.

- The above procedure was · repeated until reaching the height of 4 feet.

Thereafter, the geosynthetic-reinforced portion of the CTI deep patch was

constructed vertically until the height of 7 feet was reached, as shown in

Figures 3.1 and 3. 2, using an L-shaped form made of plywood.




duration (drop time + waiting period) of each increment.

23

3.3 TEST MATERIALS


The reinforcement used in the tests was a nonwoven heat-bonded polypropylene

geotextile. The reinforcement was described in Section 2.3.1 .

3.3.2 THE GRAVELLY SAND

The soil used in this test was a brown gravelly sand classified as A-1-B (Road

Base class 1). The soil was described in Section 2.3.2.

3.4 INSTRUMENTATION

The CTI deep patch tests were instrumented to measure their behavior during

construction and upon dropping the moveable part of the bottom panel. A number

of different instruments were used to monitor the performance of the tests. They

were two-component load cell, high-elongation strain gage, lubricated latex grid

and dial indicator. Figure 3.3 illustrates the location of instrumentation in the CTI

deep patch tests. A detailed description of instrumentation was given in Section

2.4.

24


The displacement of the CTI deep patch and the bottom panel, as measured by

the lubricated latex grid, is shown in Figure 3.4. It is noted from the figure that

the vertical part of the face of the CTI deep patch remains vertical (with very

limited lateral displacement) throughout the test. The maximum settlements of 7

and 16 inches were measured at the top of the wall corresponding, respectively,

to the 5 and 11 inches drop in the moveable part of the bottom panel. Figure 3.5

shows the CTI deep patch after removing the berm which followed the 11 inch drop

of the moveable part of the bottom panel. A gab between the bottom of the

structure and the moveable part of the bottom panel is to be noted in the figure.

A vertical crack emanating from a point on the top of the CTI deep patch near

the back panel is shown in the Figure 3.4. The crack started with the first drop

of. 0.2 inch and propagated throughout the test due to further drops of the

moveable part of the bottom panel. The depth of the crack was approximately 7 ft

and its width was approximately 1 inch due to the 11 inch drop in the moveable part

of the bottom panel.

The measured normal stress dis,tribution in the CTI test along the bottom panel

is depicted in Figure 3.6. It is to be noted from the figure that the normal stress

has substantially increased with the increase of drop of the moveable part of the

25

bottom panel in load cell #2- (located at 70 inches from the back panel, close to the

moveable part of the bottom panel). On the other hand, the normal stress in load

cell #1 (located at 97 inches from the back panel) decreased (as expected) with

increasing the drop of the moveable part of the bottom panel. The maximum stress

of approximately 12.0 psi was measured after berm removal (following the 11 inch

drop in the moveable part of the bottom panel) .

It is to be noted that the initial stresses measured in the CTI deep patch test are

higher than the initial stresses measured in the USFS unreinforced test (Figure

2.37). This is obviously due to the odd shape of the CTI deep patch.

The measured strain distribution along the geosyntl1etic layers 2, 4 and 6 located

at elevations 2, 4 and 6 feet are shown in Figures 3. 7(a), 3. 7(b), and 3. 7(c),

respectively. The maximum -strain of approximately 1.2%, corresponding to 11

inches drop of the moveable part of the bottom panel, was observed near the edge

of geosynthetic layer 2. At 11 inch-drop, the maximum strain of approximately

0.7% was observed in geosynthetic layer 4, whereas the maximum strain of

approximately 1% was observed in geosynthetic layer 6. A substantial increase in

measured strains corresponding to the removal of the berm is noted in the figures.

It is to be noted that the strains measured in the CTI deep patch test are smaller

than those measured in the reinforced USFS deep patch test.

26

3.6 THE CTI DEEP PATCH TECHNIQUE IN SILVERTHORNE

The newly developed CTI deep patch technique was used to repair a landslide

within the city of Silverthorne-Colorado in October, 1993. The cost of traditional

repair for the landslide could have easily exceeded $100,000, whereas the estimated

cost of the CTI deep patch technique was less than $15,000. This tremendous

reduction in cost could result in repairs to many present and future landslides

around Colorado that would go un-repaired or that would cost tremendous amount

of money with traditional technologies of landslide repair.

Figure 3.8 illustrates the configuration of the CTI deep patch in the Silverthorne

site. Six layers of compacted soil with geogrid reinforcement were used. The

construction procedure is very similar to the one described in Section 3.2. The

construction procedure, shown in Figure 3.9, involves making a 6 ft-deep cut in

the existing highway. The cut width was about 10 ft which was well beyond the

slip surface of the landslide. The geogrid reinforcement was then positioned on top

of the existing soil and on top of the berm which was constructed beforehand. A

1 ft-thick layer of soil was placed and compacted and the geogrid reinforcement was

wrapped around it. This was repeated until reaching the total height of 6 ft.

Figures 3.10 and 3.11 show the CTI deep patch during construction in

Silverthorne.

27


To investigate the effectiveness of the CTI deep patch technique for landslide

repair, a large-scale plane strain laboratory test was conducted. The moveable

part of the bottom panel of the plane stain apparatus was gradually dropped to

simulate progressive local landslide. The response of the CTI deep patch to the

drop was carefully monitored.

The test results showed that the CTI deep patch remained intact throughout the

test with the exception of the tolerable crack near the back panel which initiated

in the beginning of the test and propagated throughout the test. However, the

stresses exerted to the bottom panel in the CTI deep patch test were substantially

greater than those in the USFS unreinforced test. This increase in normal

stresses, due to the odd shape of the CTI deep patch, will probably aggravate the

stability of the slope which was in the state of progressive failure before the CTI

deep patch repair.

28

CHAPTER 4

THE CTI DEEP PATCH TECHNIQUE WITH SHREDDED TIRE

AS BACKFILL

4.1 INTRODUCTION

Chapter 3 described the CTI deep patch technique which evolved from the USFS

deep patch technique. In the CTI deep patch technique the top portion (5-6 feet

high) of the small-scale sliding slope under a highway pavement is removed and

then rebuilt in the form of a geosynthetic-reinforced soil "retaining wall" with a

reversed angle as shown in Figures 1.2 and 3.1.


Chapter 3 described, in detail, the first CTI test which involved the use of Road

base class 1 as backfill. In this Chapter, the second CTI test with shredded tire

as backfill is described. The unit weight of the" compacted" shredded tire backfill

used in this test is approximately 1/3 of the unit weight of the road base backfill

used in the first test.

29


- Road base (class 1) backfill was used (without compaction) to construct a 4 ft

high berm on top of the 3 inch-thick sand layer (which was placed on top of the

bottom panel) as shown in Figure 3.1. The front face of the berm has the slope

of 1 (vertical): 1.25 (horizontal). The inner face of the berm has the slope of

1:2.25.

- A sheet of geosynthetic reinforcement (long enough to wrap around the backfill

layer, i.e., the length of the sheet =2 x length of the backfill layer + the height

of the backfill layer ) was positioned on top of the 3 inch -thick sand layer. The

excess length of the sheet was positioned on top of the berm.

- Shredded tire backfill was placed on top of the geosynthetic reinforcement in 12

inch-thick lifts to construct the geosynthetic-reinforced portion of the CTI deep

patch as shown in Figure 3.1. Each lift was uniformly compacted by simply

"stepping" on top in a reasonably consistent pattern. The unit weight of the

shredded tire backfill was approximately 40 pcf. Upon completing the placement

of a layer of shredded tire, the excess length of the geosynthetic reinforcement

layer was wrapped around it.

- The above procedure was repeated until reaching the height of 4 feet.

Thereafter, the geosynthetic-reinforced portion of the CTI deep patch was

30

constructed (vertically) with compacted road base as backfill . The height of the

vertical portion, with road base backfill, was 3 feet.




duration (drop time + waiting period) of each increment .

4.3 TEST MATERIALS


The reinforcement used in the test was a nonwoven heat-bonded polypropylene

geotextile. The reinforcement was described in Section 2.3.1.

4.3.2 THE SHREDDED TIRE

The backfill material used in this test was a coarse shredded tire, with its

average grain size (chip length) of 4 to 6 inches.

A one-dimensional compression test was performed on the shredded tire prepared

at 6.3 KN / m3 (40 pcf) density. The one-dimensional compression test apparatus,

shown in Figure 4.1, consisted of a 0.5 inch-thick, 20 inch-diameter and 20 inch

high steel cylinder. The steel cylinder had one close end (the bottom end) made

31

of a 0.5 inch-thick steel plate. The inner surface of the steel cylinder was lined

with a thin layer of plexiglass. A lubrication layer made of a thin layer silicon

grease and a latex membrane was used to minimize friction between the shredded

tire and the lining plexiglass . After the shredded tire was placed in the cylinder,

a circular 0.5 inch-thick steel cover (with a diameter slightly smaller than the

diameter of the cylinder) was positioned on top. A vertical load was applied to the

steel cover using an MTS-810 machine.

The load history of the one-dimensional compression test is shown in Figure

4. 2 . As shown in the figure, the load history consists of three stages. The first

stage is a controlled load stage at a load rate of approximately 150 lb/minute which

correspond to a stress rate of 0.6 psi/minute. The second stage is a constant load

stage (creep), in which the applied load of 1500 lb (which correspond to a 6.3 psi

stress) was kept constant for 300 minutes. The third stage is a unload stage at a

unload rate of approximately 150 lb/minute (0.6 psi/minute).

The stress-strain behavior of the shredded tire under one-dimensional

compression is shown in Figure 4.3. The stress-strain behavior of the shredded

tire in the controlled load stage is nearly linear with a slight upward concavity.

Assuming a linear behavior during loading, a constant Constrained Modulus of

approximately 56.0 psi for shredded tire is estimated from the figure. Additional

32

modulus, such as Poisson's ratio, is needed to completely characterize the elastic

behavior of this material.

During the constant load stage, a significant creep can be noted in Figure 4.3.

The creep strain which occurred during the 300 minutes-period was approximately

15% of the total axial strain. Figures 4.4 and 4.5 show in arithmetic and semi

logarithmic planes, respectively, the creep behavior of shredded tire under a

constant stress of 6.3 psi.

At the end of the unload stage, as shown in Figure 4.3, most of the axi8J. strain

was recovered. Only 2% to 3% axial strain of the 12.5% total axial strain

(corresponding to 6.3 psi normal stress) was not recovered (plastic strain). Since

the applied normal stress of 6.3 psi in the one-dimensional compression test is

comparable to the maximum compaction stress normally used in the field, it is

obvious from the figure that most of the strain will be recovered as the compaction

factory is removed. Therefore, it can be concluded that ·the static compaction of

shredded tire is ineffective.

4.4 INSTRUMENTATION

The CTI deep patch test with shredded tire was instrumented to measure its

behavior during construction and upon dropping the moveable part of the bottom

33

panel. A number of different instruments were used to monitor the performance

of the tests. They were two-component load cell, lubricated latex grid and dial

indicator. A detailed description of instrumentation was given in Section 2.4.


The displacement of the CTI deep patch and the bottom panel, as measured by

the lubricated latex grid, is shown in Figure 4.6. It is noted from the figure that

the face of the CTI deep patch suffers excessive vertical and lateral displacements

throughout the test. The maximum settlements of 8 and 18 inches were measured

at the top of the wall corresponding, respectively, to the 5 and 11 inches drop in

the moveable part of the bottom panel. Lateral displacements in excess of 12 inches

were measured corresponding to the 11 inch drop of the moveable part of the

bottom panel.

A vertical crack emanating from a point on the top of the CTI deep patch near

the back panel is shown in the Figure 4.6. The crack started with the first drop

of 0.2 inch and propagated throughout the test due to further drops of the

moveable part of the bottom panel. The depth of the crack was approximately 7 ft

and its width was approximately 7 inches due to the 11 inch drop in the moveable

part of the bottom panel. It is noted from the figure that the whole structure seems

34

to be rotating clockwise with further drops in the moveable part of the bottom

panel. This rotation did not cease even after the maximum drop of 11 inches was

reached. The excessive movements and the large crack in the backfill render the

CTI deep patch technique with shredded tire as backfill unapplicable.


To investigate the effectiveness of the CTI deep patch technique (with shredded

tire as backfill) for landslide repair, a large-scale plane strain laboratory test was

conducted. The moveable part of the bottom panel of the plane stain apparatus was

gradually dropped to simulate progressive local landslide . The response of the CTI

deep patch to the drop was carefully monitored.

The test results showed that the CTI deep patch with shredded tire backfill

suffered excessive movements throughout the test. A large crack near the back

panel initiated in the beginning of the test and propagated throughout the test.

The depth of the crack was approximately 7 ft and its width was approximately 7

inches due to the 11 inch drop in the moveable part of the 1:;lottom panel. The whole

structure seems to be rotating clockwise with further drops in the moveable part

of the bottom panel. This rotation did not cease even after the maximum drop of

11 inches was reached. The excessive movements and the large crack in the

35

backfill render the CTI deep patch technique with shredded tire as backfill

unapplicable.

36

CHAPTER 5

SUMMARY AND CONCLUSIONS

5.1 SUMMARY

The USFS deep patch technique involves the removal of the top portion (5-6

feet-high) of the small-scale sliding slope under a highway pavement and

rebuilding that portion with the use of horizontal layers of geosynthetic inclusions.

This study was aimed at investigating the effectiveness of the USFS deep patch

technique in (1) reducing the adverse effects of local landslides on highway

pavement and (2) increasing the stability of the repaired slope by reducing applied

normal stresses exerted to its top. The investigation was accomplished by devising

a large-scale apparatus in which the USFS deep patch technique can be closely

simulated. Two USFS large-scale deep patch te'sts were conducted. The first test,

termed "the USFS unreinforced test", used a compacted backfill without

geosynthetic reinforcement, whereas the second test, termed "the USFS reinforced

test", used the same soil for backfill as the USFS unreinforced test along with five

37

equally-spaced horizontal Iayers of geosynthetic reinforcement.

Another deep patch technique, evolved from the USFS deep patch technique,

was also investigated. This technique, named the CTI (Colorado Transportation

Institute) deep patch technique, was suggested by Professor ZhenghuanLiao from

Chongqing University (P. R. of China). In the CTI deep patch technique the top

portion (5-6 feet-high) of the small-scale sliding slope under a highway pavement

is removed and then rebuilt in the form of a geosynthetic-reinforced soil "retaining

wall" with a reversed angle.


advantage is the tolerance of the CTI deep patch to any subsequent settlement of.

the repaired slope. If there is a tendency of further settlement in the repaired

slope, the geosynthetic-reinforced portion of the CTI deep patch will separate from

the repaired slope causing no distress in the highway pavement. The second

advantage of using the CTI deep patch technique is its ability to widen the highway

of an average of 4 feet.


Road base class 1 backfill was used in the first CTI deep patch test, and shredded

tire backfill, which weighs approximately 1/3 of the road base backfill, was used

in the second CTI deep patch test.

38

5.2 CONCLUSIONS

The USFS deep patch tests results showed that the unreinforced slope suffered

a severe distress throughout the test. A large vertical crack initiated in the

beginning of the USFS unreinforced test and propagated throughout the test to the

extent that the slope was virtually separated into two parts. On the other hand,

the reinforced slope remained intact throughout the test with the exception of the

few cracks initiated in the beginning of the test but were suppressed by the

geosynthetic reinforcements.

The stresses exerted on the moveable part of the bottom panel in the USFS

reinforced test were substantially smaller than those in the USFS unreinforced

test. This reduction in stresses will enhance the stability of the slope which was

in the state of progressive failure before the USFS deep patch repair.

This USFS tests results showed that (1) the USFS deep patch repair reduced

effectively the adverse effects of local landslides on highway pavement by

preventing crack propagation, and (2) the USFS deep patch increased the

stability of the repaired slope, which was in progressive failure, by reducing the

stresses exerted to it.

The CTI deep patch test (with road base as backfill) results showed that the CTI

deep patch remained intact throughout the test with the exception of the tolerable

39

crack near the back panel which initiated in the beginning of the test and

propagated throughout the test. However, the stresses exerted to the bottom

panel in the CTI deep patch test were substantially greater than those in the USFS

unreinforced test. This increase in normal stresses, due to the odd shape of the

CTI deep patch, will probably aggravate the stability of the slope which was in the

state of progressive failure before the CTI deep patch repair.

The CTI deep patch test (with shredded tire as backfill) results showed that the

CTI deep patch suffered excessive movements throughout the test. A large crack

near the back panel initiated in the beginning of the test and propagated

excessively throughout the test. The depth of the crack was approximately 7 ft

and its width was approximately 7 inches due to the 11 inch drop in the moveable

part of the bottom panel. The whole structure seems to be rotating clockwise with

further drops in the moveable part of the bottom panel. This rotation did not cease

even after the maximum drop of 11 inches was reached. The excessive movements

and the large crack in the backfill render the CTI deep patch technique, with

shredded tire as backfill, unapplicable.

40

REFERENCES

Billiard, J. W. 1989. Performance of a Large Scale Fabric Wall During Load Test. M.S. Thesis, University of Colorado at Denver.

Billiard, J. W. and Wu, J. T. H. (1991). "Load Test of A Large-Scale GeotextileReinforced Retaining Wall. " Proceedings of Geosynthetics '91 Conference, Atlanta, Georgia, pp. 537-548

Helwany, M. B. (1993). "The Long-Term Behavior of Geosynthetic-Reinforced Soil Structures." Ph.D. Thesis, University of Colorado at Boulder.

Helwany, M. B. and Wu, J. T. H. (1994)."In-Confinement Creep Characteristics of Geotextiles." To be submitted to ASTM Geotechnical Testing Journal.

Huang, C. C. and Tatsuoka, F. (1990). " Bearing Capacity of Reinforced Horizontal Sandy Ground." Geotextiles and Geomembranes, Vol. 9, pp. 51-82.

Tatsuoka, F., Molenkamp, F., Torti, T. and Hino, T. (1984). "Behavior of Lubrication Layers of Platens in Element Tests." Soils and Foundations, vol. 24, No.1, pp. 113-128.

Wu, J. T. H. (1991). "Measuring Inherent Load-Extension Properties of Geotextiles for Design of Geosynthetic-reinforced Structures. " ASTM Geotechnical Testing Journal, Vol. 14, No.2, June 1991, pp. 157-165.

Wu, J. T. H. (1992a). "Predicting Performance of the Denver Walls: General Report." Geosynthetic-Reinforced Soil Retaining Walls, Wu (editor), Balkema Publisher, pp. 3-20.

Wu, J. T. H. (1992b). "Construction and Instrumentation of the Denver Walls." Geosynthetic-Reinforced Soil Retaining Walls, Wu (editor) , Balkema Publisher, pp. 21-30.

41

8 ft

"" ... ........ ............

(c)

SURCHARGE

......... fa) .... , \

' ... ''''''''

" , , , -, ... , \ ,

\ ,

(b)

, ... ... , , , ,

" , ... ,

.....

PAVEMENT

OCAL~SUDE 40-50 ft

... , , " FILL .....

..... .... ..... , ...... ..... ....... ..........

GEOSYNTHETIC

~ ____ ~~~~~~~ O~CEMENT

PANEL

Figure 1.1 Schematic Diagram of the USFS Deep Patch Technique

42

8ft

SURCHARGE

, , , ,

HIGHWAY PA VEMENr

, .. , , ,

GEOSYNTHETIC

~ __ -=~~~~ruaNFORCE~ . /

, , , .. , ..... ..... .....

..... ' .....

7 ft ----.1~* .. If---- 9 ft -.....lI_~ 3 ft DROPPING PANEL

Figure 1.2 Schematic Diagram of the CTI Deep Patch Technique

43

Figure 2. 1 The Deep Patch Test Awaratus

44

Fig~ 2.2 The Front Cranl.: which Oper-c.tes the Front Th.,0\l Jacks

45

:':""igu:-e The Back Crank whi.::h Opera:es Front Two Jacks

--

48

tension ... --_.

1.· stationary clamps

2. cover clamps ./ ./ ~2

3. bolt /1 / // r /3

4. geosynthetic reinforcement ./' ./' ./' ./' V J' 0

5. epoxy-reinforced ends of geosynthetic reinforcement

of:>, 1.0

1

5

4

5

1

T I / tension

Figure 2.6 Schematic Diagram of the Uniaxial Load-Deformation Apparatus

Fig'.!:"e 2.7 Th~ 'Uni2xjal Load-Deformation Test

5 (

[) I

I '

Figurf~ ? R Stee:l Mold fur Epoxy A ppli cation on the Two Hnds of the Geotextile Specimen

tn t»

Figure 2.9 Assembly of Steel Mold for Epoxy Application on the Two Rnds of the Ueotextile Specimen

1.00

0.90

0.80

0.70

I/) 0.60 c. ~ - 0.50 '0

as 0

0.40 ...J

0.30

0.20

0.10

0.00 0.00 0.04 0.08 0.12 0.16 0.20

Strain

Figure 2.10 Load-Deformation Behavior of the Geotextile Reinforcement

53

100

90

80

70 "-CD c:: 60 -- 50 c:: CD 0 ... 40 CD Q.

30

20

10

0 0.001 0.01

: ::: t . ···11 . "'11

: : ::::":

: : :::=i. · . : :1:: · . ~1::~

v······ .... -.. . · ..... . ······v· · . .... . · . .... . · . .... . · . .... . · . .... .

· . ::¥: · .7::: ·······A····· · . ..... . ..... . · . ..... . ..... . · . ..... . ..... . · . ...... . ...... . ....... . ...... .

0.1 . 1 10

grain diameter, mm

100

Figure 2.11 Grain Size Distribution Curve of the Gravelly Sand

54

130

126 -0 Q.

- 122 .r:. C)

CD ~ -c: 118 :::s >. ~

~

114

11 0 I..--..L._"""'----'""---'-_-'-_""--..L._ ....... _'----'

5 6 7 8 9 10 11 12 13 14 15

water content, %

Figure 2.12 . Compaction Curve of the Gravelly Sand

55

111 0\

C\l c:

" ..tI

'" > Q)

"'0 -jd

E Cl

11l

120

l01ZJ

B0

S0

40

20

Figure 2. 1 3 (a) -------.. ----

Triaxial ,Compression Test Results for the Gravelly Sand

UI feb 1994 1S~4Sz 15

I' 1 T-· --- ---T I -"-- -'---l

• I I

-_ ... ---L------I

__ . __ ... ___ .. -'-_____ 1 ______ 1-_._._.___ ___ ~ II Ji i I .----- ----.- -... ----... ----.... ~----.-.... '---'---' --~

I . ~ . t ~- .~~t-----+---J.-.

--~-.-- ----- ·---.. ·-t--·-----I I I I o 1i---J'---____ ... --l ___ .. ___ L ___ 1 _ L __ l "

B 2 LEGEND

4 B B 10 12 14 18 19 ·20

SYM~OL SPi~IMEN Ax 1 a 1 St r a: in - ~ x 32

l * 33 rea.ture Sample 1 Class. symbol ROAD BASE COMPACTED

Liquid " mft Plasttc l ty Index Spectflc gravIty 2.60 Project UCD Depth ft. Test Type CD

- ------ . ~---- .. --.--. ---------~.-.-.--------------------. --------------_._--_._---.. _-------------_ .... _----

U1 -.J

...:

Q) m

I~

l~ E :J -0 >

-- ~ ----.-------. - - ._-- -~ --~---------. __ .------.-._--- ------.. _- --- _._-_..-----.. --. --- ---.... --... --~.--- -. ---'---- -""--- -.... --.---.~.- ... _----. --.,-- ------- ----------

Figure 2.13(b) Triaxial Compression Test Results for the Gravelly Sand

10 Feb 1994 15:54:29

Volume Plot Pore Pressure Plot

10

9

9

7

6

5

4

3

2

1

0 0

-----r--- '- '- --l---T----<--·--1·-.. ·----- ---- ----- .--- -._.- "--l--i----.. ------+-- --- ----- .-.--- ----- ---1-- 1--

~_~i~~.tj~_ ~--_.=~~~=-'-=~j~~-.j~:--I.---l-L------L---J.-------L~---_i--

I

.-.-- -- ··------1-----·-- -.-_.- ----.-.1---~ ~

-=[:=:~ =~~:.:·I·=:-~ --~:±=_= ~= ~=t=-~~= ~- - - ~

2 4 B B 10 12 14 16 18 20

Axia l Strain - Y.

LEGEND

.9

.9 N C ... "\ .7 .a

.6 ., L :::J .5 ~

" ., L a. .4 ., L 0 .3 a.

" ~ .2 Q)

" x w

• 1

I!J I!J 2 4 6 B 10 12 14 16 18

Ax 1 a 1 Str a 1 n - Y.

212

SYMBOL SPECIMEN o 31 X 32 * 33 Feature

L f qu f d 1 f m f t Project UCD

Samp l e 1 Class . symbo l ROAD BASE Plastfcity I ndex Specific gravIty 2.S0

Depth ft. Test Type CD

COMPACTED

__ ... , ..... -_ ....... _ ...... _. __ ... · ...... ___ 0-· ...... _. ____ . _______ ._ .. ,_. __ ... ____ ,. .......... _______ ..---_ ..... ~_. ____ • __ .. _. ____ ._ .. __ • __ .... __ ., .... _-.-... ___ .. ______ .... ___ .•. _ ... _. ___ • __ ...... __ .... ____ • _______ •• _____ • __ ... _ __.. ". _________ ..

U1 co

SURCHARGE

. l~~~:.. 3 ~ ----lJr-- -"7't:.--- - &1.- - - - 8--- __

--- --- ------ - -- ____ ~ I - ____ - ----- -. -----

_~c:y_eE -~A- _____ A- - ---- -8- - - - - -8- - - - - -b-- - --

6 high-elongation strain gage

~ two-component load cell

. 2 displacement dial gages

@ lubricated latex grid

-- ---- --- .----- ----- - - - - -. - -- -----. - -- -- --- - -----

layer 1 A A ___ A -------i::z-------~--------------M-------M---- ~

6 5 4 3 2

Figure 2.14 Instrumentation of the USFS Deep Patch Test

t.n \0

1

input

c ' 'd ' , , .!:zz::1 tz:z:: , " , " , , ,

f

t1 c I I d

:t:?~ I I I I

shear stress 3

output

4 <:==:>

Full Bridge

2 (b)

(a )

c

normal stress

4

d b - - I J - 1

2

3

-a

liLtli

Bottom panel

normal

stress ~ c::=.=n

shear stress

perpendicular to paper'

steel container

Vertical Cross-Section of the Bottom Panel

( C)

Figure 2.15 Schematic Diagram of the Two-Component Load Cell

61

.-" < -.

1100

1000

0 900

:: 0 800 + cell # 1 > 0 ... u 700 E t:. cell # 2 CD 600 CD c:

500 0 cell # 3 CIS .c 0 CD 400 CD + cell # 4 CIS

300 !:: 0 >

200

100

0 0 3 6 9 12 15

Normal Stress, psi

Figure 2.20 Normal Stress Calibration Curves for Load Cell

64

Figure 2.21 Snear SLress Calibration of Load ee:l

55

5000 r------------,

tI.I 4000 -0 + cell # 1 > 0 ... . 2 E 3000 t- celi # 2 CD 0) C 0 cell # 3 «I

.J:: 0 2000

CD cell # 4 0) +

as !:: 0 > 1000

o 4 8 12 16 20

Shear Stress, psi

Figure 2.22 Shear Stress Calibration Curves for Load Cell

66

.sa

69

;S .~

~ > c U

.5

70

30

27

24

I/) 21 -0_ >1/) 18 01J (j C .- as E I/) 15 = • 0 .... CD,c

I-' ~t:. 12 !:: 0 > 9

6

3

0

calibration curves for strain gages

+

+

0 4 8 12 16 20

strain. %

Figure 2.27 Calibration Curve for Strain Gage

gages 1. 2 3 and 4

".J 1'0

l::'iigure 2.28 Environmental and Mechanical Protection of Strain Gages Using a layer of Neoprene :Rubber

Figure 2.29 Geotextile Layer Instn::mented \\ith Strain Gages-

- ., . -

I 1

i4

I

-1 I

•

75

-..J C'\

w/o Reinforcement

surcharge ~ crack

5432 1

Legend 1 end of construction 2 2.0"drop 3 5.0"drop 4 8.0"drop 5 11.0"drop

Figure 2.32 Displacement Field of the Backfill in the Unreinforced USFS Deep Patch Test

--I >,.,

Figure 2.33 The Crack Corrt'sponding to 11 inch · Drop in the Unreinforced USPS Deep Patch Test

-...J 0)

wI Reinforcement

crack (5)

surcharge

crack (5)

---------------------------------

-------------------------------------~~,

______ ~ Reinforcement ------------- - --- ----- - - - -- ---

Legend 1 end of construction 2 2.0"drop 3 5.0"drop 4 8.0"drop 5 11.0"drop

---------- - - ------- ---- --------- - - - -------- ~-~-"...

------------------------------------------------~~~~ 54321

Figure 2.34 Displacement Field of the Backfill in the Reinforced USFS Deep Patch Test

" 1.0

SURCHARGE

Figure 2.35(a)

"' "'. "', "" , ,

" , , ""'.... 2.0 INCH DROP ,

"""', , , " , , , , ,

" " ",

Comparison of Crack Propagation in the Two Tests at 2 inch-Drop

"

co o

SURCHARGE

Figure 2.35(b)

5.0 INCH DROP


co I-'

SURCHARGE

Figure 2.35(c)

8.0 INCH DROP


co to.)

SURCHARGE

Figure 2.35(d)

11.0 INCH DROP


crack propagation

+ wlo reinf. A w/reinf.

100

90

80 In CD .c 70 0 r::

~ 60

0 as 50 ... 0 -0 40 .c -C) 30 r::

CD

20

10

0 0.00 2.20 4.40 6.60 8.80 11.00

settlement, inches

Figure 2.36 Comparison of Crack Propagation in the Two Tests

83

normal stress, w/o reinforcement

7

6 + end of construction

5 6 1 inch tn c.. drop iii

4 tn 0 2 inch Ql ~ -tn

ca 3 E

+ 3 inch ~

0 c:

2 • 8 inch

1 • 11 inch

0 0 28 56 84 112 140 168 196

distance from back, inches

Figure 2.37 Distribution of Nonnal Stresses along the Bottom Panel in the Unreinforced USFS Deep Patch Test

84

normal stress, wI reinforcement

7

6 + end of

construction 5

(/) A 1 inch a.. 1/)-

4 I/)

GI

drop

0 2 inch ... -I/)

~ 3 E + 3 inch ... 0 c

2 • 8 inch

1 • 11 inch

0 0 28 56 84 112 140 168 196


Figure 2.38 Distribution of Nonnal Stresses along the Bottom Panel in the Reinforced USFS Deep Patch Test

85

4

3

'#. c 2 tIS .... -II)

1

0 0

Figure 2.39(a)

+ end of strain distribution in layer 1 construction

t. .2" drop

0 .4"

+ .6"

• 1.0"

• 1.5"

v 2.0"

<> 3.0"

c 5.0"

.. 8.0"

• • 11.0"

27 54 81 108 135 162


Distribution of Strain along the Geosynthetic Reinforcement Layer 1 in the Reinforced USFS Deep Patch Test

86

+ end of

strain distribution in layer 3 construction IJ. .2" drop

4 r-------------------------------~ 0 .4"

3

-c cu 2 .... -(f.J

1

o

Figure 2.39(b)

+ .6"

4 1.0"

• 1.5"

v 2.0"

0 3.0"

0 5.0"

• B.O"

• 11.0"

23 46 69 92 115 138



87

4.00

3.20

'#. 2.40

c tIJ .... -(/)

1.60

0.80

0.00 0.00

Figure 2.39(c)

+ end of strain distribution in layer 5 construction

11 .2" drop

0 .4"

+ .6"

A 1.0"

• 1.5"

v 2.0"

<> 3.0"

0 5.0"

y 8.0"

• 11.0"

18.17 36.33 54.50 72.67 90.83 109.00



88

L GEOSYNTHETIC REINFORCEMENT

(X) t-\C ~

....... / ,"" t,12.25 1.25~ I /1 .".-5 A N D i

-7 FT. I 1.5 FT. I 7.5 FT.

Figure 3.1 Schematic Diagram of the CTI Deep Patch Test

Figure 3.2 Tna en Deep Patzh Test at End of Construttior:

90

10 ,....

!-I-!- 1-1-!-

4

I

layer 6 A A A A A L.J. L...J. -~ L...J. L...J.

layer 4 A A A A J\ L...J. ~ ~ ~ ~

7 layer 2 A A A A A

~ ~ ~ ~

~7 2.25

-1

3 2 1 / ..---. ...

l

Figure 3.3 Instrumentation of the CTI Deep Patch Test

-.. ..

6 high-elongation strain gage

~ two-component load cell

. 2 displacement dial gages

.x grid

1 ~ 1.25~

U)

I\l

~ LL .......

5" drop

11" drop

Displacement Scale

12"

- =='- = = == = ==::..=. = ==~======= == ====-===_1

7FT 9FT

Figure 3.4 Displacement Field of the Backfill in the CTIDeep Patch Test with Road Base Backfill

"

Figure 3.5 The Deformed Face c: tlJe eTr Deep Patch Test with Roa.d B.:se Backfill after Removing the Berm

Figure 3.6 Distribution of Normal Stresses along the Bottom Panel in the en Deep Patch Test with Road Base Backfill

94

strain distribution in layer 1

2 ~--------------------------------~

~ -c 1

CIS ... -f/)

oL---~~~~~~~~--~ 40 56 72 88 104 120


. + end of construction

1" drop

o 2" drop

+ 3" drop

4 8" drop

• 11" drop

v after berm removal

Figure 3.7(a) Distribution of Strain along the Geosynthetic Reinforcement Layer 2 in the en Deep Patch Test with Road Base Backfill

95

strain distribution in layer 2

2.00 ,..--------------------,

1.60

'#. 1.20

c:: 'iii .... -{I) 0.80

0.40

0.00 40 56 72 88 104 120


+

0

+

..

•

v

end of construction

1" drop

2" drop

3" drop

8" drop

11" drop

after berm removal

Figure 3.7(b) Distribution of Strain along the Geosynthetic Reinforcement Layer 2 in the en Deep Patch Test with Road Base Eackfl11

96

+ end of

strain distribution in layer 3 co nstructi on

A 1 n drop

2.00

0 2" drop

1.60

+ 3" drop

"$. 1.20

c: 4 8" drop cu ... -0

0.80

• 11" drop

0.40 v after berm

removal

0.00 40 56 72 88 104 120


Figure 3.7(c) Distribution of Strain along the Geosynthetic Reinforcement layer 6 in the eTI Deep Patch Test with Road Base Backfill

97

"> <XI

I 3ft

SILVERTHORNE, COLORADO October 26, 1993

Guardrail

II .... -' ... , ... .. .. .. -.------; .... ~

u 6 ft

..... - " ..

10-12 % slope

/--2 ft -I" 7 ft ..,

Figure 3.8 Configuration of the CTI Deep Patch in Silverthorne

\0 \0

CONSTRUCTION

6ft

1 berm

Figure 3.9 Construction Procedure of the CTI Deep Patch in Silverthorne

o C"-l

II

detailed section

aPPliedloadf

Diameter = 18 inch .

(1) steel container (2) plexiglass liner (3) silicone grease (4) latex membrane

£J.gure 4.1 Schematic Diagram of the One-Dimensional Compression Test for Shredded Tire

102

.... rrl ~

.n rrl ~ ... ~ rrl

.... = 8 ... 0 I::

7

r··· "!*..: • 'p.

6

5

4-

: 3:

2'

1

0 0 50 100 150 200 250 300 350

time. minutes

Figure 4.2 The Load History of the One-Dimensional Compression Test on Shredded Tire

103

.... 171 j:l,

ci 171 ~ ~ ... 171 ... CIS

S ~ 0 I::

10

9

8

7

6

5

4

.' 3

2

1

0 0 2 4 6 8 10 12 14

axial strain, %

:Figure 4.3 Stress-Strain Behavior of the Shredded Tire under One-Dimensional Compression

104

!;oI!

a .... ell ~ ~ I'll -CIS .... ~ ell

12.8

12.6

12.4-

12.2

12

11.8: . ,

11.6

11.4-

11.2

11 0 50 . 100 150 200 250 300

time, minutes

Figure 4.4 Creep Behavior of Shredded Tire under a Constant Stress of 6.3 psi (arithmetic)

105

~

d .... ell

'"' ~ en -ell .... >< C\l

12.8

12.6

12.4

12.2 .., /"

,/ 12 . ..-.--'-.--_.-.....

. .. ..

11.8

11.6

11.4

11.2 10-1 100 101 102 103

time, minutes

Figure 4.5 Creep· Behavior of Shredded Tire under a Constant Stress of 6.3 psi (semi-logarithmic) . -

106

...... a ...:I

"

5 inch drop 11 inch drop

r--------------------~ -- .... - ... _--I Road Base - ___ _ , '-r Road Base ------------Road Base ---------------

-----------Shredded Tire

Shredded Tire

Shredded Tire

--Shredded Tire

\ , , J

'\

I

I Displacement Scale

12"

------------------- --------- --- ------- -- -- - -- - - - - - - - - - - - - - - - -- - - - - --

Figure 4.6 Displacement Field of the CTI Deep Patch Test with Shredded Tire Backfill

Documents

The Deep Patch Technique for Landslide Repair · technique for repairing landslides with geosynthetic reinforcement. The technique involves replacing sections of roadway lost due