EXPEIUMENTAL AND NUMERICAL INVESTIGATION · 2005. 2. 11. · The design of soil-geotextile systems...

EXPEIUMENTAL AND NUMERICAL INVESTIGATION

OF INFILTRATION PONDING IN ONE-DIMENSIONAL

SAND-GEOTEXTILE COLUMNS

ALVIN FELIX HO, B.A.Sc. (Toronto)

A thesis submitted to the Department of Civil Engineering

in conformity with the requirements for the

degree of Master of Science (Engineering)

Queen's University

Kingston, Ontario, Canada

September, 2000

Copyright O Alvin F. Ho, 2000

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The design of soil-geotextile systems for filtration and separation applications

under saturated tlow conditions is well-established. However. in most applications. the

geotextile and adjacent soil exist in an unsaturated condition for much of their design life.

Only limited information on the unsaturated hydraulic properties and unsaturated tlow

behaviour of geotextile materials is available in the literature. It has been proposed that a

potential problem that may develop in road bases and reinforced soil retaining walls is the

ponding of water in the soil above a geotextile layer during or after a surface water

infiltration event. Associated with potential water ponding are transient elevated pore-

water pressures (ponding pressures) that may create additional hydrostatic or seepage

forces, increase lateral flow of water, reduce effective stresses in the soil. and increase

soil unit weights. These effects are not routinely accounted for in design.

The research reported in this thesis is focused on the characterization of the

unsaturated hydraulic properties of selected woven and non-woven geotextiles prepared

in new and contaminated conditions, and the behaviour of these materials under

simulated infiltration loading in a senes of one-dimensional experimental sand/sand-

geotextile column tests. Numerical models were calibrated against the physical test

results and the models were used to investigate the hydraulic response of a wider range of

sand-geotextile combinations under infiltration loading.

Experimentaily determined geotextile-water characteristic c w e s showed that the

geotextiles exhibited very steep and hysteretic dryhg and wetting-paths. The water

characteristic curves and results of calibrated numerical models suggest that the

maximum hydraulic conductivity during wetting-up of a geotextile under low suction

heads is very much lower than the value of the reference saturated hydraulic conductivity

of the geotextile determined from conventional permittivity testing. This reduced

hydraulic conductivity was shown to be the cause of water ponding in numerical models.

Expenmental and numerical column tests showed that ponding of water above a

geotextile layer is possible with geotextiles that have reference saturated hydraulic

conductivity values less than that of the adjacent sand. The potential for infiltration

ponding can be avoided by adopting conventional filter design rules for grotextile-soi1

systerns under saturated flow conditions.

1 would like to express my gratitude to my thesis supervisor. Professor Richard J.

Bathurst for his excellent guidance and constant support throughout the course of this

thesis. It was an inspiring and invaluable expenence working with him over the past two

years. Also. I would like to express my appreciation to Dr. D. Chenaf for her advice on

the numerical modeling section of this research project. and Dr. S. Vanapalli for his

suggestions on the experimental design.

My appreciation is also extended to Mr. Tom Baker and Ms. Sandy Jones of

Amoco Fabrics and Fibres Company (now British Petroleum) for financial support and

the supply of geotextile sarnples.

Recognition is offered to the technical support staff of the Royal Milit- College

of Canada. particularly to Mr. Joe DiPietrantonio of the Department of Civil Engineering

for his contribution in constnicting the experimentai apparatus for the research program.

and Mr. Jim Irving of the Department of Chernistry and Chernical Engineering for his

help in taking the scanning electron microscope photographs of the geotextile specimens.

1 would also like to take this oppomuiity to thank my parents. This work would

not have been completed without their love, encouragement and support.

And last, but not least, my thanks to Ms. Beckie Li for her patience during the last

two years of my graduate studies.

i i i

................................................................................ ABSTRACT.. .............................................................. ACKNOWLEDGEMENTS..

........................................... .............. TABLE OF CONTENTS.. ,...... LlST OF

LlST OF

LlST OF

LIST OF

LlST OF

TABLES ................. .... ................................................. FIGURES ................... ......a................. NOTATIONS.. ...................................................................

............................................................. ABBREVl ATlONS .............................................................. CONVERSIONS..

i

i i i

iv

xi

xiii

xxix

xxxiii

xxxiv

CHAPTER 1 INTRODUCTION ................................................... 1

....................................................................... 1.1 BACKGROUND 1

.......................... 1.2 OUTLINE AND OBJECTIVES OF THE RESEARCH 3

1.3 THEESEARCHPROGRAM .................................................... 5

......................................................... 1.4 THESIS ORGANLZATION 6

CHAPTER 2 1lTERATURE REVIEW...... ....................................... 8

................................................................... 2.1 INTRODUCTION.. 8

2.2 ONE-DIMENSIONAL UNSATURATED FLOW JN POROUS MEDIA..,. 8

2.3 UNSATURATED HYDMULIC PROPERTIES OF SOIL MATERIALS.. IO

2.3.1 Saturation-Suction Relationship ............................................... 10

2.3.2 Soil-Water Characteristic Cuve ............................................... 10 2.3.3 Hydraulic Conductivity-Suction Relationship .............................. 12

........................................................................ GEOTEXTILES

............... 2.5 HYDR4ULIC PROPERTIES OF GEOTEXTILE MATENALS 13

2.5.1 Saturated Hydraulic Properties ................................................. 13

2.5.2 Unsaturated Hydrauiic Properties .............................................. 15

2.5.2.1 Bormoni . Henry and Evans (1 99 7) .................................... 15 2.5.2.2 Stormoni and Morris (2000) ........................................... 17

2.6 NUMERICAL MODELING OF SAND/SAND-

GEOTEXTILE COLUMNS ......................................................... 18

CHAPTER 3 EXPERIMENTAL DESIGN ........................................ 29

................................................................... 3.1 INTRODUCTION

3.2 ONE-DIMJ3SIONAL SAND/SAND-GEOTEXTILE

................................................................... COLUMN TESTS

..................................................................... Tensiometers ............................................................ Pressure Transducers

Calibration of Tensiometer-Transducer Devices ............................ ............................................................ Conductivity Probes ............................................................ Soi1 Extraction Ports

. . . Data Acquisition System ....................................................... ................................................ Air Channels and Manometers

....................................................... Constant-Head Reservo ir ................................................................ Free Water Table

Geotextile Layer .................................................................

...... 3.3 MEASUREMENT OF SOIL-WATER CHARACTERISTIC CURVE 37

3.4 MEASUREMENT OF GEOTEXTILE-WATER

CHARACTERISTIC CURVES ................................................... 38

3.5 MEASUREMENT OF THICKNESS OF GEOTEXTILES UNDER

VERTICAL CONFINNG PRESSURE .......................................... 40

CHAPTER 4 EXPERIMENTAL METHODOLOGY ............................. 58

4.1 ONE-DIMENSIONAL SANDISAND-GEOTEXTILE

COLUMN TESTS ................................................................... 58

...... 4.2 MEASUREMENT OF SOIL-WATER CHARACTEFUSTIC CURVE 60

4.3 MEASUREMENT OF GEOTEXTILE-WATER

CHARACTERISTIC CURVES ................................................... 61

4.4 MEASUREMENT OF THICKNESS OF GEOTEXTILES UNDER

VERTICAL CONFNNG f RESSURE .......................................... 63

CHAPTER 5 MECHANICAL AND HYDRAULIC PROPERTIES OF

....................... SAND AND G EOTEXTI LE MATE RIALS 69

5.1 INTRODUCTION ................................................................... 69

5.2 PROPERTIES OF SAND ........................................................... 70

5.2.1 Partide Size Distribution ....................................................... 70 5.2.2 Specific Gravity .................................................................. 71 5.2.3 Dry Density ........................................................................ 71 5.2.4 Void Ratio and Porosity ......................................................... 72 5.2.5 Water Content and Degree of Saturation ..................................... 72

...................................... 5.2.6 Dry Unit Weight and Bulk Unit Weight

............................................. 5.2.7 Saturated Hydraulic Conductivity

................................................... 5.2.8 Surnrnary of Sand Properties

.................... 5.3 SOIL-WATER CHARACTERISTIC CURVE FOR SAND

5.4 COMPARISON OF SATURATION-SUCTION MEASUREMENTS

FROM DRAR'JED COLUMN TESTS AND SOIL-WATER

CHAIUCTERISTIC CURVE .......................................................

5.5 PROPERTIES OF NEW GEOTEXTILES ........................................

5.5.1 Mass Per Unit Area ..............................................................

5.5.2 Apparent Opening Size ......................................................... 5.5.3 Specific Gravity of Polypropylene Material ................................. 5.5.4 Thickness of Geotextiles under Vertical Confining Pressure ..............

................................................... 5 3.5 Porosity of New Geotextiles

........................ 5.5.6 Permittivity and Saturated Hydraulic Conductivity ...................................... 5.5.7 Summary of New Geotextile Properties

5.6 PROPERTIES OF CONTAMINATED GEOTEXTILES .......................

5.6.1 Properties of Kaolin Clay ....................................................... 5.6.2 Preparation of Contaminated Geotextile Sarnples ........................... 5.6.3 Porosity of Contarninated Geotextiles ........................................ 5.6.4 Permittivity and Saturated Hydraulic Conductivity ........................ 5.6.5 Summary of Contaminated Geotextile Properties ...........................

5.7 GEOTEXTILE-WATER CHARACTERISTIC CURVES

FOR GEOTEXTILES ................................................................

5.7.1 Non- Woven Geotextiles.. ....................................................... 5.7.2 Woven Geotextiles ...............................................................

vii

5.8 SCANNING ELECTRON MICROSCOPE IMAGES OF

EXPERIMENTAL MATERIAL S ..................................................

CHAPTER 6 RESULTS OF EXPERIMENTAL SANDISAND

GEOTEXTILE COLUMN TESTS .................................

6.1 ONE-DIMENSIONAL SAND/SAND-GEOTEXTILE

..................................................................... COLUMN TESTS

6.2 INTERPRETATION OF CONDUCTIVITY PROBE AND

TENSIOMETER-TRANSDUCER RESPONSES ................................

6.3 INFILTRATION WETTTNG.FRONT .............................................

....................... 6.4 TRANSIENT PORE-WATER PRESSURE RESPONSE

6.1.1 1 -D Sand Column Test (Test 1) ................................................

.......................... 6.4.2 1 -D Sand-Geotextile Column Tests (Tests 2 to 5)

6.5 INFLUENCE OF GEOTEXTILE LAYER ON INFILTRATION

.............................................................. PONDING PRESSURE

CHAPTER 7 NUMERICAL MODELING AND RESULTS OF

PARAMETRIC ANALYSE .........................................

.................................................................... 7.1 INTRODUCTION

7.2 NUMENCAL SIMULATION OF ONE-DIMENSIONAL

SANDISAND-GEOTEXTILE COLUMN TESTS ...............................

7.2.1 General Anangement and Material Properties ..............................

7.2.2 WH1 Unsat SuiteNS2D Program ............................................. 7.2.3 Brooks and Corey Mode1 for Sand and Geotextiles .........................

7.2.4 Calibration of Numerical 1 -D Sand/Sand-Geotextile

ColumnModels .................................................................. 140

................................................... 7.3.4.1 1-Dsandcoltrmnresrs 141

7.2.4.2 I -D sand-geotextile colurnn tests ....................................... 112

7.2.4.3 Discussion of sources of discrepancy behwen nlrnzerical cintl

................. experimen ta1 transient pore-wu fer response cirn7es 144

................... 7 . 4 4 Adjrrstmenl of hydraulic properties oj'geore.rrilrs 146

7.3 RESULTS OF PARAMETRIC NUMERICAL ANALYSIS ................ 148

7.3.1 NumericalTestPrograrn ......................................................... 148 7.3.2 1 -D Numericd Sand Column Tests ........................................... 149

7.3.3 1 -D Numericd Sand-Geotextile Column Tests .............................. 150

7.3.4 Sumrnary .......................................................................... 152

CHAPTER 8 CONCLUSIONS. IMPLICATIONS TO DESIGN AND

RECOMMENOATIONS FOR FURTHER RESEARCH ......

.................................................................... INTRODUCTION

UNSATURATED HYDRAULIC PROPERTIES OF WOVEN

AND NON-WOVEN GEOTEXTILES ............................................

RESULTS OF EXPERiMENTAL ONE-DIMENSIONAL

................................ SAND/SAND GEOTEXTlLE COLUMN TESTS

RESULTS OF NUMERICAL SIMULATIONS OF ONE-

......... DIMENSIONAL SAND/SAND GEOTEXTILE COLLJMN TESTS

RESULTS OF NUMERICAL PARAMETRIC ANALYSIS OF

.......... ONE-DIMENSIONAL SANDIS AND-GEOTEXTILE COLUMNS

8.6 IMPLICATIONS TO DESIGN AND PERFOEUUANCE OF

GEOTEXTILE-SAND LAYERS UNDER SURFACE

NFILTRATION LOADING.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i 94

8.7 RECOMMENDATIONS FOR FURTHER RESEARCH.. . . . . . . . . . . . . . . . . . . . .. 195

CHAPTER 9 REFERENCES.. . . . .. . .. . .. . . ... . .. . . . .. . . . . . . . . . . . . . . . . . . . 197

APPENDIX A CALIBRATION AND RESPONSE TIME OF 202

TENSIOMETER-TRANSDUCER DEVICES ........ .. .... .. ..

A. 1 INTRODUCTION.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... . . . . . . . . . . . . . . . . . . . . . . .. . . . 202

A.2 CALIBRATION OF TENSIOMETER-TIWNSDUCER DEVICES.. . . . . . . . 202

A.3 RESPONSE TIME OF TENSIOMETER-TRANSDUCER DEVICE

FROM FALLING-HEAD TEST.. . . . . . . . .. . .. . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . 204

LIST OF TABLES

Table 2.1 Properties of the non-woven geotextiles tested by Palmeira

................................................... md Gaidori (2000) 20

Table 2.2 Propenies of the non-woven. needle-punched. polypropylene

geotextiles investigated by Stormont et al. (1 997). .............. 2 1

Table 2.3 Properties of the non-woven geotextiles investigated by

....................................... Stormont and Moms (3000).. 2 1

Table 3.1 Number and location of monitoring instrumentation and soi1

extraction ports mounted on the one-dimensional (1-D)

sandsand-geotextile colurnn test apparatus.. ...................... 42

............................. Table 5.1 Properties of washed JETMAG sand.. 9 1

....................... Table 5.2 Properties of "new" geotextile specimens.. 92

............ Table 5.3 Properties of "contarninated" geotextile specimens.. 92

Table 6.1 Experimentd program of one-dimensional (1 -D) sand/sand-

geotextile column tests.. .............................................. 1 17

Table 7.1 Brooks and Corey (1964) parameters and properties of sand

and geotextile materials used for nurnencal simulations of

experimental one-dimensional (1 -D) sandknd-geotextile

column tests.. .......................................................... 154

Table 7.2 Summary of hydraulic conductivity values for numerical

parametric analysis ................................................... 155

Table A.1 Summary of the linear calibntion equations for the

tensiometer-transducer devices ...................................... 206

LIST OF FIGURES

Figure 2.1 Typical soil-water characteristic c w e s (SWCCs) for various

......... 1 3 (4) volcanic sand (from Fredlund and Rahardjo 1993).. --

Figure 2.2 SWCCs for typical gravelly and silty sands (from Shoop and

............................................................ Henry 1991) 23

Figure23 Relative hydraulic conductivity as a fùnction of matric

suction during drying and wetting cycles of a fine sand soi1

(from Brooks and Corey 1964) ..................................... 24

Figure 2.4 Variation of geotextile normal pemeability with normal

stress for virgin non-woven geotextile specimens: (a) average

geotextile thickness venus normal stress; (b) normal

pemeability venus normal stress (fiom Palmeira and Gardoni

2000). .................................................................. 25

Figure 2.5 Wetting and drying-paths of the geotextile-water

characteristic curves (GWCCs) for new geotextile specimens:

(a) A l , (b)A2, (c) B1.and (d) B2 (from Stormont etal. 1997) 26

Figure 2.6 Wetting and drying-paths of the GWCCs for cleaned

geotextile specimens: (a) A 1, (b) A.2, ( c ) B 1, and (d) B2 (fiom

Stormont et al. 1997). ................................................. 27

xiii

Figure 2.7 GWCCs for polyester non-woven geotextiles with intruded

soi1 (fiom Stormont and Morris 2000) .............................. 28

Figure 3.1 One-dimensional (1 -D) sandkand-geotextile column test

apparatus (height of column is 2 15 cm) ............................ 43

Figure 3.2 Sc hematic of instrumented 1 -D sand/sand-geotextile colurnn

test apparatus presented in two different side views .............. 44

....... Figure 3.3 Mid-section of the 1 -D sandkand column test apparatus 45

Figure 3.1 Schematic of tensiometer installed through wall of the 1-D

sandkand-geotextile colurnn test apparatus and connected to a

pressure transducer .................................................... 45

Figure 3.5 Tensiometer assembly ................................................. 16

Figure 3.6 Motorola MPX 2 100 GP pressure transducer ...................... 16

Figure 3.7 Schematic of conductivity probe installed through wall of the

1 -D sand/sand-geotextile column test apparatus .................. 47

................................................... Figure 3.8 Conductivity probes 47

Figure 3.9 HP 3497A data acquisition system used to record voltage

...... signals fiom pressure transducers and conductivity probes 48

Figure3.10 Penonal cornputer used to control the HP 3497A data

acquisition system during the 1 -D sand/sand-geotextile

column tests ............................................................ 49

xiv

Figure 3.1 1 Customized user interface designed using HP 3055 data

logger software.. ...................................................... 49

Figure 3.12 Air channels and manometers connected to the manometer

board. ................................................................... 5 O

Figure 3.13 Drainage system at bottom of the 1-D sandsand-geotextile

column testapparatus .................................................. 50

Figure 3.14 Schematic of geotextile specimen arrangement in the sand-

geotextile colurnn test apparatus.. .................................. 5 1

Figure 3.15 Woven geotextile (Amoco 2044) specimen placed in the

sand-geotextile column test apparatus.. ............................ 5 1

Figure 3.16 Schematic of the Tempe ce11 used to determine the soil-water

characteristic curve (SWCC) for sand.. ............................ 52

...... Figure 3.17 Test arrangement used to determine the SWCC for sand.. 53

Figure 3.18 Tempe ceIl used to determine the S WCC for sand ............... 5 3

Figure 3.19 Schematic of the suction plate apparatus used to determine the

geotextile-water characteristic curves (GWCCs) for

.............................................................. geotextiles 54

Figure 3.20 Suction plate apparatus used to detemine the GWCCs.. ....... 55

Figure 3.21 Temperature and humidity control chamber for the suction

........................................................ plate apparatus. 55

Figure 3.22 Schematic of the test apparatus used to measure the thickness

of a geotextile specimen under an applied venical confining

pressure ................................................................. 56

Figure 3.23 Setup of the test apparatus used to rneasure the thickness of a

geotextile specimen under an applied vertical confining

................................................................. pressure 57

Figure 3.24 Loading plates (10 cm x 10 cm) used to confine a geotextile

specimen under an applied vertical confining pressure .......... 57

Figure 4.1 Preparation of saturated sand specimen ............................ 64

Figure 4.2 Adjustment of the water level in the ballast tube (from

. Soilmoisture Equipment Corp 1983) ................................ 65

Figure 4.3 Preparation of saturated geotextile specimen ..................... 66

........ Figure 4.4 Saturation of a geotextile specimen with carbon dioxide 67

............... Figure 4.5 Geotextile specimen subrnerged in de-aired water 67

Figure 4.6 Electronic scale with an accuracy o f f 0.0 1 g ..................... 68

Figure 4.7 Measurement of the initial thickness of a geotextile specimen

using vernier calipers ................................................. 68

Figure 5.1 Particle size distributions of original and washed JETMAG

sand .................................................................... 93

xvi

Figure 5.2

Figure 5.3

Figure 5.1

Figure 5.5

Figure 5.6

Figure 5.7

Figure 5.8

Figure 5.9

Bulk unit weight-saturation relationship of the washed

JETMAG sand as-placed in the one-dimensional (1 -D)

..................................... sandfsand-geotextile colurnns.. 93

Measured soil-water characteristic cuve (SWCC) for the

............................................. washed JETMAG sand.. 94

Predicted and measured SWCC for the washed JETMAG

sand using Brooks and Corey mode1 ( 1964). ...................... 94

Saturation profiles of the one-dimensional (1 -D) sand/sand-

geotextile columns after draining for 20 minutes (short-tem

..................................................................... tests) 95

Saturation profiles of the 1 -D sand/sand-geotextile columns

after draining for 24 hours (long-term tests). ...................... 96

Measured saturation-suction in 1 -D sand/sand-geotextile

columns after draining for 20 minutes (short-term tests). ....... 97

Measured saturation-suction in 1 -D sand/sand-geo textile

columns after draining for 24 hours (long-term tests). ........... 97

Reduction in thickness of new woven and new non-woven

geotextile specimens versus vertical confïning pressure. The

thickness and porosity of the woven and non-woven

geotextiles under 16 kPa (i.e. 120 cm-hi& column of dry

sand) are highlighted in the figure..

xvii

Figure 5.10 Kaolin powder used to artificially contaminate geotextile

.................................................................. samples 99

Figure 5.1 1 Preparation of contaminated geotextile sample. Kaolin paste

was rubbed into the geotextile ....................................... 99

Figure 5.12 Comparison of new and contaminated woven geotextile

specimens (Amoco 2044). ........................................... 100

Figure 5.13 Comparison of new and contarninated non-woven geotextile

specimens (Arnoco 45 16). ........................................... 100

Figure 5.14 Measured geotextile-water characteristic curve (GWCC) for

the new non-woven geotextile.. ..................................... 10 1

Figure 5.15 Measured GWCC for the contaminated non-woven geotextile. 10 1

................ Figure 5.16 Measured GWCC for the new woven geotextile.. 102

.... Figure 5.17 Measured G WCC for the contaminated woven geotextile.. 1 02

Figure 5.18 S c a ~ i n g electron microscope (SEM) image of the washed

IETMAG sand at 13x rnagnification.. ............................. 103

Figure519 SEM image of the washed JETMAG sand at 30x

magnification.. ........................................................ 103

Figure 5.20 SEM image of the new woven geotextile (Amoco 2044) at

1 3 ~ magnification.. ................................................... 1 04

xviii

Figure 5.21 SEM image of the new woven geotextile (Arnoco 2044) at

88x magnification.. ................................................ 104

Figure 5.22

Figure 5.23

Figure 5.24

SEM image of the contaminated woven geotexti

2044) at 13x magnification.. ........................... le (Arnoco

.............

SEM image of the contaminated woven geotextile (Amoco

2044) at 88x magnification. .........................................

SEM image of the new non-woven geotextile (Amoco 35 16)

at 13x magnification.. ................................................

Figure 5.25 SEM image of the new non-woven geotextile (Arnoco 4516)

at 88x magnification.. ................................................ 1 06

Figure 5.26 SEM image of the contarninated non-woven geotextile

(Amoco 45 16) at 1 3x magnification. ............................... 1 07

Figure 5.27 SEM image of the contaminated non-woven geotextile

(Amoco 45 16) at 8 8 ~ magnification.. .............................. 107

Figure 6.1 Interpretation of conductivity probe response: (a) normalized

voltage reading venus time; and (b) rate of change of

normalized voltage reading-tirne plot.. ............................ 1 18

Figure 6.2 Interpretation of tensiometer-transducer response: (a) pore-

water pressure versus time; (b) normalized pore-water

pressure versus time; and (c) dope of pore-water pressure-

tirne plot.. .............................................................. 1 19

xix

Figure 6.3 Advancement of the infiltration wetting-front detected by the

conductivity probes.. ................................................. 1 70

Figure 6.4 Advancement of the infiltration wetting-front detected by the

tensiometer-transducer devices.. .................................... 1 2 1

Figure 6.5 Amval times for the wetting-front to reach the free water

table and time to develop 90% of hydrostatic pressure in the

one-dimensional (1 -D) sand/sand-geotextile columns detected

by the tensiometer-transducer devices. ............................. 1 22

Figure 6.6 Transient pore-water pressure responses at elevation of 13 1

cm above datum and 36 cm above the geotextile layer (T 1). .. 123

Figure 6.7 Transient pore-water pressure responses at elevation of 1 1 8

cm above datum and 23 cm above the geotextile layer (T2). .. 124

Figure 6.8 Transient pore-water pressure responses at elevation of 1 14

cm above datum and 19 cm above the geotextile layer (T3). ... 125

Figure 6.9 Transient pore-water pressure responses at elevation of 109

.. cm above datum and 14 cm above the geotextile layer (T4). 126

Figure 6.10 Transient pore-water pressure responses at elevation of 104

cm above datum and 9 cm above the geotextile layer (T5). ..... 127

Figure 6.11 Transient pore-water pressure responses at elevation of 99 cm

above d a m and 4 cm above the geotextile Iayer (T6). .......... 128


above datum and 5 cm below the geotextile layer (T7) ........... 129


above datum and 8 cm below the geotextile layer (T8).. ......... 130


above datum and 12 cm below the geotextile layer (T9) ......... 13 1

Figure 6.15 Maximum ponding pressure above geotextile layer located at

120 cm depth in the 1-D sand-geotextile column with respect

to the saturated hydraulic conductivity (Ksa,) of geotextile

..................................................................... layer 132

Figure 6.16 Maximum ponding pressure above geotextile layer located ai

120 cm depth in the 1-D sand-geotextile column with respect

to the saturated hydraulic conductivity ratio. KsOrlJand, /

............................................................. K-,,/,, 133

Figure 7.1 Numencal one-dimensional ( 1 -D) sand/sand-geotextile

coiumn.. ................................................................ 156

Figure 7.2 User interface for the computer program WHI Unsat Suite

(1999). .................................................................. 157

Figure 7.3 Material properties input dialog box for the computer

program WHILlnsatSuite(1999) ................................... 157

Figure 7.4 Predicted and measured geotextile-water characteristic curve

(GWCC) for the new woven geotextile using Brooks and

Corey mode1 ( 1 964). .................................................. 1 5 8

Figure 7.5 Predicted and measured GWCC for the contaminated woven

geotextile using Brooks and Corey mode1 (1 964) ................ 158

Figure 7.6 Predicted and measured GWCC for the new non-woven

eeotextile using Brooks and Corey mode1 (1 964). ............... i 59 C

Figure 7.7 Predicted and rneasured GWCC for the contaminated non-

woven geotextile using Brooks and Corey mode1 ( 1 964). ....... 1 59

Figure 7.8 Assurned water characteristic curves for sand and geotextile

materials using Brooks and Corey mode1 (1 964): ( 1 ) washed

JETMAG sand; (2) new woven geotextile; (3) contaminated

woven geotextile; (4) new non-woven geotextile; and (5)

contaminated non-woven geotextile.. .............................. 160

Figure 7.9 Initial hydraulic conductivity-suction curves for sand and

geotextile materials using Brooks and Corey model (1964):

(1) washed ETMAG sand; (2) new woven geotextile; (3)

contarninated woven geotextile; (4) new non-woven

geotextile; and (5) contarninated non-woven geotextile.. ....... 16 1

Figure 7.10 Transient pore-water pressure response at depth of 84 cm (T 1)

for expenmental and numerical sand column tests (Test 1 ). .... 162

Figure 7.11 Transient pore-water pressure response at depth of 97 cm (T2)

for experimental and numerical sand column tests (Test 1). .... 162

Figure 7.12 Transient pore-water pressure response at depth of 10 1 cm

(T3) for experirnental and numencal sand column tests (Test

Figure 7.13 Transient pore-water pressure response at depth of 106 cm

(T4) for experimental and numerical sand colurnn tests (Test

1) ........................................................................ 163


(T5) for experimental and numerical sand column tests (Test

1) ....................................................................... 164


(T6) for experimental and numerical sand column tests (Test

1 ) ....................................................................... 164

Figure 7.16 Transient pore-water pressure response at depth of 84 cm (Tl)

for experimental and numerical sand-geotextile colurnn tests

(Test 2). ................................................................. 165

Figure 7.17 Transient pore-water pressure response at depth of 97 cm (T2)

for experimental and numencal sand-geotextile column tests

(Test 2). ................................................................. 165


(T3) for experimental and nurnencal sand-geotextile column

tests (Test 2). .. ... ...................................................... 1 66


(T 4) for experimental and numencal sand-geotextile CO lumn

tests (Test 2). ........................................................... 166

Figure 7.20 Transient pore-water pressure response at depth of 1 1 1 cm

(T5) for experirnental and numerical sand-geo texti le CO lumn

tests (Test 2). ........................................................... 167


(T6) for expenmental and numerical sand-geotextile column

tests (Test 2).. .......................................................... 167


(T3) for expenmental and numerical sand-geotextile column

tests (Test 3.. .......................................................... 168

Figure 7.23 Transient pore-water pressure response at depth of I l I cm

(T5) for expenmental and numerical sand-geotextile colurnn

tests (Test 3). ........................................................... 168


(T3) for experirnental and numericai sand-geotextile column

tests(Test4) ............................................................ 169

Figure 7.25 Tmsient pore-water pressure response at depth of 1 11 cm

(T5) for experirnental and numerical sand-geotextile column

tests(Test4) ............................................................ 169

xxiv


(T3) for experirnental and numerical sand-geotextile colurnn

tests (Test 5). ........................................................... 170

Figure 7.27 Transient pore-water pressure response at depth of 1 1 1 cm

(T5) for experimental and numerical sand-geotextile column

tests (Test 5). ........................................................... 1 70

Figure 7.28 Adjustment factors to calculate the mâuimurn hydraulic

conductivity of geotextiles in numerical sand-geotextilr

columns during wetting.. ............................................ 1 7 1

Figure 7.29 Original and adjusted hydraulic conductivity curves for the

new woven geotextile.. .............................................. 172


contaminated woven geotextile.. .................................. 1 72


new non-woven geotextile.. ......................................... 173


.. contarninated non-woven geotextile.. .......................... .. 1 73

Figure 733 Hydraulic conductivity curves for sand layers in numencal 1 - D sand/sand-geotextile column tests simulations (parametnc

analysis) using Brooks and Corey mode1 (1 964). ................. 174

Figure 7 3 4 Saturation versus depth for numerical 1-D sand colurnn with

.................... Sand(1)only(Test 1). K541(Jd)=2940~~/hr 175

Figure 7.35 Pore-water pressure venus depth for numerical 1-D sand

C O ~ I I I with Sand (1) o d y (Test 1 ). Ksa,lsand, = 2940 CM.. .. 176

Figure 7.36 Saturation versus depth for numerical 1-D sand column with

Sand (4) oniy (Test 16). Ksol~sand, = 368 c m . . . . . . . . . . . . . . . . . . .. 177

Figure 7.37

Figure 7.38

Figure 7.39

Figure 7.40

Figure 7.41

Figure 7.42

Pore-water pressure versus depth for numencal 1-D sand

colurnnwithSand(4)only(Test 16). KsalIsand,=368cm/hr .... 178

Saturation versus depth for numerical 1 -D sand-geotextile

column with Sand (1) and new woven geotextile (Test 2).

Ksar(SQnd~ = 2940 CM and K, l (g ,o~ , le , = 237 CM.. . . . . . . . . . . .. 179

Pore-water pressure versus depth for numerical 1-D sand-

geotextile column with Sand ( 1 ) and new woven geotextile

(Test2). K,l~s~d~=3940cm/hrandKsDfIg~o~~l,l,~=237cm/hr.. 180

Saturation versus depth for numerical 1 -D sand-geotextile

colurnn with Sand (4) and new woven geotextile (Test 17).

K S C I f ~ s a n d ~ = 3 6 8 ~ m / h r ~ ~ d K s a l ~ ~ o ~ , l , ~ = 2 3 7 ~ ~ ~ h ï ............... 181

Pore-water pressure venus depth for numerical 1-D sand-

geotextile colurnn with Sand (4) and new woven geotextile

(Test 1 7). K.,(nd, = 368 c d h r and Ksatl~o,af,~d = 23 7 cm/hr.. 1 82

Saturation versus depth for numencal 1 -D sand-geotextile

column with Sand (3) and new woven geotextile (Test 12).

Figure 7.43 Pore-water pressure versus depth for numerical 1 -D sand-

geotextile column with Sand (3) and new woven geotextile

(Test 12). Ksa t l sd=735~m/hrandKsa f~~m, ,1e ,=237~mihr . . 184

Figure 7.44 Saturation versus depth for nurnencal 1-D sand-geotextile

colurnn with Sand (3) and new woven geotextile (Test 15).

.............. = 73 5 c r n h and k;,,,,,,,k, = 1 7 1 cm/hr. 1 8 5

Figure 7.45 Pore-water pressure venus depth for numencal 1-D sand-

geotextile column with Sand (3) and new woven geotextile

(Test 15). K,,~sad~=735~m/hrandKsar~,or ,r i~r i= 171 cm/hr.. 186

Figure 7.46 Maximum ponding pressure above geotextile layer located ar

120 cm depth in the 1 -D sand-geotextile column with respect

to the saturated hydraulic conductivity (k,,) of sand layer.. .... 187

Figure 7.17 Maximum ponding pressure above geotextile iayer located at

120 cm depth in the I-D sand-geotextile colurnn with respect

to the saturated hydraulic conductivity ratio. KsarlJand, 1

Km(,,owd,> 1 ......................................................... 188

Figure A.1 Calibration apparatus setup for the iensiorneter-transducer

device ................................................................... 207

Figure A.2 Example voltage response of tensiometer-transducer device to

change in pressure = 1 kPa.. ........................................ 208

Figure A.3 Cali bration curve for tensiometer-transducer device T 1 ......... 209

Figure A.4 Experimental setup for measuring the response time of the

tensiometer-transducer device ....................................... 2 10

Figure A.5 Pressure head with respect to time observed by the

conductivity probes and tensiometer-transducer device ......... 2 1 1

LIST OF NOTATIONS

Basic SI units are given in parentheses.

ares of gmtestilc specimen (m2)

apparent opening size of geotextile (m)

D ~ ~ ' 1 (Dao x Dlo) = coefficient of curvature (dimensionless)

DbO / ilIO = coefficient of uniformity (dimensionless)

water capacity function as a function of pressure head (m*')

particle diarneter corresponding to 1 0% by mass of

finer particles (m)

particle diameter corresponding to 30% by mass of

finer particles (m)

particle diarneter corresponding to 60% by mass of

finer particles (m)

void ratio (dimensionless)

gravitational acceleration (m/s2)

specific gravity (dimensionless)

pressure head (m)

air-entry suction head (m)

break-point suction head on water characteristic cuve (m)

ponding head (m)

maximum ponding head (m)

xxix

suction head (m)

water-entry suction head (m)

hydraulic conductivi ty (m/s)

maximum hydraulic conductivity during wetting (m/s)

relative hydraulic conductivi ty (dirnensionless)

sanirated hydraulic conductivity (mk)

saturated hydraulic conductivity of geotextile (mk)

saturated hydraulic conductivity of sand ( d s )

saturated hydraulic conductivity of soi1 (m/s)

mass per unit area of geotextile ( ~ g / r n ' )

mass of fines per unit area of geotextile (~glrn')

mass of sand (Mg)

m a s of water (Mg)

porosity (dimensionless)

recharge rate ( d s )

degree of saturation (dirnensionless)

effective saturation (dimensionless)

maximum saturation (dimensionless)

residual saturation (dimensionless)

time (s)

thickness of geotextile (m)

initiai thickness of geotextile (m)

air pressure (Pa)

ponding pressure (Pa)

maximum ponding pressure (Pa)

pore-water pressure (Pa)

90% of maximum pore-water pressure (Pa)

maximum pore-water pressure (Pa)

voltage (V)

maximum voltage (V)

volume of solids (m3)

total volume (m3)

volume of voids (m3)

volume of water (m3)

water content (dimensionless)

depth below surface (m)

Kmfwef,n@ / K',~geo,,,,Ie, = adjustment factor for saturated

hydraulic conductivity of geotextile during wetting

(dimensionless)

bulk unit weight of soil @J/rn3)

dry unit weight of soi1 (Wrn3)

saturated unit weight of soil (N/rn3)

unit weight of water (Mn3)

Brooks and Corey (1964) pore-size distribution index for

porous media (dimensiodess)

Vw l V, = volumetric water content fdirnensionless)

dry density ( ~ ~ / r n ' )

density of geotextile fibres ( ~ g / r n ~ )

density of soi1 particles ( ~ g / r n ~ )

density of water ( ~ g / r n ~ )

x-ticr! cocfining press- (Pa)

geotextile clogging parameter (dimensionless)

geotextile critical clogging parameter (dimensionless)

permittivity (s'l)

LIST OF ABBREVIATIONS

2-D

ASTM

C

GWCC

M

S

SEM

SWCC

T

uscs

one-dimensional

two-dimensional

Amencan Society for Testing and Materials

conductivity probe

geotextile-water characteristic curve

manometer or air channel

soi1 extraction port

scanning electron microscope

soil-water characteristic curve

tensiometer-transducer device

Unified Soi1 Classification System

LIST OF CONVERSIONS

PRESSURE

1 cm of water = 0.097899 kPa

I bar = 100 kPa

FLOW RATE

1 ds = 360,000 c m h

CHAPTER 1

INTRODUCTION

1.1 BACKGROUND

Geotextiles are geosynthetic products that are used in combination with soils to

constnict earth structures. They are manufactured as continuous sheets from woven. non-

woven or kniaed fibres of synthetic polymer materials (typically polyester or

polypropylene). The sheets are flexible, penneable and generally have the appearance of

a fabric. The most common applications for geotextiles are separation of soil layers with

dissimilar particle size distributions, filtration and lateral drainage. Non-woven

geotextiles comprised of entangled polymeric fibres or filaments are typically used for

separation, filtration and drainage applications. Woven geotextiles comprised of strips of

polymeric filaments, yarns or films have also been used for soil reinforcement

applications.

In hydraulic applications, the geotextile product must be selected so that: (1) the

geotextile has adequate permeability to transmit water in the cross-plane and/or in-plane

direction; (2) adjacent soi1 particles do not migrate across the geotextile layer. and: (3)

the geotextile does not clog intemally with soi! fines that rnay be carried by fluid Ilows.

Well-established design methods are available to ensure hlfillment of these criteria

assuming that the geotextile and soil are subjected to saturated flow conditions (e.g. Holtz

et al. 1997 and Koemer 1998). However. in many applications. the geotextile and

adjacent soi1 exist in an unsaturated condition for much of their design Me.

Consequently. the geotextile and adjacent soil must change from an unsaturatrd to a

saturated state before the conditions for which the geotextile were designed actually

~ P P ~ Y .

While the saturated hydraulic properties and sanirated flow behaviour of

geotextiles in combination with different soil types are well understood. very little

information is available on the unsaturated hydraulic properties and unsaturated flow

behaviour of these materials. Lirnited data reported by Stormont et al. (1997) suggests

that non-woven çeotextiles may have very low hydraulic conductivity in an unsaturated

condition.

Geotextiles have been proposed as capillary breaks below pavements to prevent

upward migration of water that may contribute to fiost heave and soi1 sofiening during

thawing (Henry and Holtz 1997). However, the same capillary break mechanism may act

as an impediment to downward flow of surface infiltrated water due to the reduced

hydraulic conductivity of the geotextile under low suction pressures (negative pore-water

pressures) (Stormont and Moms 2000). A consequence of low hydraulic conductivity of

the geotextile may be ponding (or mounding) of infiltration water and generation of

ponding pressure above the geotextile that couid possibly weaken the pavement structure.

Bathurst and Knight (1999) investigated the potential problem of infiltration water

ponding over woven geotextiles that are used as horizontal reinforcement layers in the

unsaturated granular backfill of geosynthetic reinforced soil walls. In this scrnario.

ponded water could increase the weight of the backfill soil. reduce effective stresses and

possibly introduce additional transient hydrostatic pressures or lateral water flows dong

the geotextile for which the retaining wall was not designed. The hydraulic conditions

required to develop infiltration water ponding (ponding pressure) over a typical woven

geotextile in a well-draining sand were identified using a series of one-dimensional ( 1 -D)

nurnencal sand-geotextile column tests. However, a c ~ a i unsaturated hydraulic

properties of woven geotextiles were not available at the time of the Bathurst and Knight

snidy and the numerical simulations were not verified against physical experiments using

similar configured sand-geotextile columns.

The lack of knowledge of the unsaturated hydraulic properties of geotextiles and

the hydraulic behaviour of initiaily unsaturated soil-geotextile layered systems under a

continuou recharge of infiltration water has led to the program of research work

described herein.

1.2 O U T L N AND OELJECTIVES OF THE RESEARCH

The primary objective of the research project was to carry out physical and

numencd experiments to better understand the 1 -D unsaturatedkaturated flow behaviour

of Iayered sand-geotextile systems under conditions of surface water infiltration. The

quantities of interest were the transient pore-water pressure response and the

corresponding wetting-front propagation pattern in these systems.

The water characteristic curves of typical woven and non-woven geotextile

products prepared in new and contaminated conditions were measured independently

using a specially manufactured suction plate apparatus.

The same geotextile materials were placed in a sand column and the column was

subjected to an infiltration recharge (1 -D sand-geotextile colurnn tests). The column was

inscnimented with tensiometrr-transducer devices and conductivity probes to quantify the

hydraulic response of the systems.

A senes of 1-D numencal sand/sand-geotextile colurnn simulations based on the

classical 1-D variable porous medium unsaturated/saturated tlow problem was used to

sirnulate the experimental sand/sand-geotextile column tests. The boundary value

problem was solved nurnerically using a commercially available compter software

package. The input parameters for the nurnerical rnodels simulating the experimental

sand-geotextile column tests were adjusted to improve the agreement between the

predicted and measured results. The adjusted input parameters were then used to carry

out a parametnc analysis representing a wider range of sand materials than the sand used

in the expenmental sand/geotextile column tests.

The results of the research are summarized and the implications of the

experimental and nurnerical results to the unsanirated/saturated flow behaviour of sand-

geotextile layers under conditions of infiltration loading are identified. Finally.

recornrnendations for M e r research are presented.

1.3 THE RESEARCH PROGRAM

In order to meet the general objectives of the research program. the following

tasks were performed by the witer:

Review of the related Iiterature on unsaturatedsaturated tlow behaviour of sands

and geotextiles.

Design and construction of an instrumented 1-D sand/sand-geotextilç column test

apparatus to rneasure the transient unsaturated/saturated hydraulic response of

sand and sand-geotextile layers under simulated surface water infiltration loading.

A control experirnent with a 1-D sand colurnn comprising of a single layer of

coarse sand was canied out.

A series of 1-D sand-geotextile colurnn tests was carried out with single layer

inclusions of typical geotextile materials conditioned in a new or contaminated

state.

The soil-water characteristic cuve (SWCC) of the coarse sand used in the colurnn

tests was determined using a commercially available Tempe cell.

The geotextile-water characteristic c w e s (GWCCs) for the new and

contaminated geotextiles were determined using a suction plate apparatus.

The saturated hydraulic properties of the sand and geotextile materials were

measured and the thickness of the geotextiles under vertical confining pressure

was determined.

Parameters for the Brooks and Corey (1964) unsaturated/saturated flow mode1

were estimated for both the sand and geotextile materials based on expenmentaily

determined SWCC. GWCC. and saturated hydraulic conductivity data of the same

materials.

Numerical models of the 1-D sand/sand-geotextile column tests using the

computer program IW Unsar Sirire (1999) were developed to sirnulate the

experimental sand/sand-geo textile column tests.

The numerical models used to predict the transient pore-water pressure responses

of the experimental column tests were calibrated against measured data.

A parametnc analysis using the calibrated numerical models was carried out to

investigate the influence of a wider range of sand materials on the 1-D

unsaturated/saturated flow behaviour of the sand-geotextile column tests.

Test results were summarized and implications of experimental and numerical

results to the potential problem of infiltration water ponding over geotextiles in

draining sand backfills were identified.

Finally. recomrnendations were made to continue the line of investigation initiated

in this research program.

1.4 THESIS ORGANTZATION

This thesis is organized into eight chapters.

Chapter 1 - Inîroduction: The general problem to be investigated is introduced.

objectives of the research stated and thesis organization presented.

Chapter 2 - Literuture Review : The classical theory of 1 -D unsaniratedkanirated flow in porous media is presented. Previous limited research on the mechanical and

hydraulic properties of geotextiles in the context of unsaturatedisaturated flow through sand-

geotextile layers is reviewed.

Chapter 3 - Erperimental Design: Details of the experimental setup and

equipment used in the research prograrn are presented.

Chapter 4 - Erperimentd Methodology: The experimental procedures for the

physical tests undertaken in the research program are discussed.

Chapter 5 - Mechunical and Hydradic Properries of' .%znd und Georrxrile

Materials: The properties of the sand and geotextile marerials used in the experimental

sandfsand-geotextile column tests are presented.

C hapter 6 - Results of Lrperimental SandISand-Geotextile Ckdtrmn Tests: The

results of the physical 1-D sandfsand-geotextile column tests carried out in the research

program are presented.

Chapter 7 - Numerical Modeling and Reslrlîs of Pararnetric Anaiysis: Details of

the numerical modeling technique used to simulate the 1 -D sand/sand-geotextile column

tests are described. The numerical models are calibrated against the physical sandfsand-

geotextile column tests and a parametnc analysis is carried out to investigate the

influence of a wider range of sand materials on the hydraulic response of the 1-D sand-

geotextile systems.

Chapter 8 - Conclusions, Implications to Design and Recommendations for

Further Research: The results of the research program are summarized and the

implications of experimental and numerical 1 -D sand-geotextile column test results to

field performance are identified. Recornmendations for future studies are also provided

in the c hapter.

CHAPTER 2

LITERATURE REVIEW

2.1 INTRODUCTION

In this chapter, the classical theory of one-dimensional (1-D) unsaturated flow in

porous media is presented and concepts of soi1 water characteristic curves (SWCCs) and

hydradic conductivity-suction behaviour of soils are introduced. Previous limited

research on the mechanical and hydradic properties of geotextiles in the context of

unsanü;ited/sanirated flow through sand-geotextile layen is reviewed.

2.2 ONE-DIMENSIONAL UNSATURATED FLOW IN POROUS MEDIA

The theoretical framework for the current investigation into unsaturated/saturated

flow in sandlsand-geotextile colurnns is the classical 1-D variable porous medium

unsaturated/saturated flow problem. Quantities of interest at any time and depth are

volumetric water content (or degree of saturation), hydrauiic conductivity and pressure

head. The partial differentiai expression describing the relationship between these

quantities under conditions of 1-D unsaturated flow is described by the matric potential

form of Richard's equation (Jury et al. 199 1):

where: h = pressure head; t = time; 2 = depth below ground surface: and K(h) = hydraulic

conductivity described as a function of pressure head. The water capacity function. C,,.(h)

is defined as:

where 8 = volumetric water content.

It shouid be noted that Richard's equation assumes a priori that the air phase in a

porous medium provides no resistance to water flow.

Equation 2.1 cm be solved numerically if two boundary conditions and an initial

condition are given, and expressions for C,(h) and K(h) are known. Finite element

methods (e.g. SEEP/W 1998) and finite difference techniques (e.g. Freeze 1969 and

Lappala et al. 1987) have been routinely used to solve this classicai boundary value

problem.

2.3 UNSATURATED HYDRAULIC PROPERTIES OF SOIL MATERIALS

2.3.: Saturation-Suction Relationship

The degree of saturation (or water content. iv) of a porous medium (e.g. soil)

decreases with increasing suction (i.e. pressure head becomes increasingly more

negative). It is convenient to normalize the degee of saturation in a porous medium

using a dimensionless parameter called the effective saturation. Se , and expressed as:

where: Sr = residual saturation (limiting saturation level at high suction values). Hence. a

porous medium in which ail voids are filled with water has an effective saturation of

unity (or 100%) and the sarne medium at minimum saturation level will have an effective

saturation of Se = O (or 0%).

23.2 SoiI- Water Characteristic Curve

The soil-water characteristic curve (SWCC) is the conventional term used in

geotechnical engineering to descnbe the relationship between the degree of saturation of

a soi1 and matric suction. (u, - u,) (usually represented by suction head, h,). The SWCCs

of soi1 materials can be determined experimentally using specialized equipment such as

the Tempe ce11 or pressure plate apparatus. The SWCC is measured by placing a soil

specimen on a high air-entry ceramic plate located in a pressure control chamber

apparatus. The variation in degree of saturation (or water content) with respect to a

range of applied rnatnc suction values is measured to determine the SWCC. Details of

expenmentai procedures and specialized equipment used to determine the SWCC of a

soi1 are reported by Fredlund and Rahardjo (1993).

Figure 2.1 shows typical SWCCs for various soils. The following features of

SWCCs for soils c m be noted in the figure: The slopes (&S/Afib - ir,,.)) of the curves are

steeper for soils with larger particle andor more uniform distributions of particle sizes.

Also, the air-entry suction pressure (or head) that appears as the break-point on a SWCC

c w e at high saturation values, is greater for finer grained soils. The air-entry suction

pressure is the minimum suction that causes air to displace water in the soi1 pores during

drying.

Soils generally have hysteretic SWCCs depending on whether the soi1 is

exsorbing water (drying) or absorbing water (wetting). However, the degree of hysteresis

is larger for finer-grained soils as s h o w in Figure 2.2. For coane sands and gravels, the

drying and wetting-paths of the SWCCs may be very similar.

A nurnber of empincal relationships between effective saturation and matric

suction can be found in the literature (Brooks and Corey 1964. Haverkamp et al. 1977,

and van Genuchten 1980). The simplest relationship is the Brooks and Corey (1964)

mode1 expressed as:

Se(hs) = 1 .O for h, r hb

whcrc: ilh hrçnk-point siiciii~ii 1ic:id (çqiiiviilciit io ihç iiir-ctiiry siictiiiti Iic;id. I r , , . oi,

drying-putli); hT siiction Iiciiti; ;ind A porc-sizc ilistrihiiiioii ii~tlcx (iliiiiçiisii~t~lcss)

rcliitcd i o thc porc-six disirihiiiiori of tliç soil.

Similiir to 111c rdwt io~i i n siiiur;ttion t h i ~ i ucctirs ili a soi1 wilh i ~ w t x i t i p , t ~ i i i t r i ~

sijction. ;i çorrcspi)riding rcdiiciiori in Iiytlr;iiiliç contliictivity ciici iilso hc çspccictl. A

liinct ion dcscribing tlic hydrwlic coiidiictivity-siict ioii rcl:t~ioiiship tOr ;I soi l is rcqiiircd

to solvc Richiird's cqiiaiion (Kquation 2.1 ) inirotluçctl ciirlicr. A 11w111cr 01' tlicorics iirc

ii~iiiliihlc in ilic 1 itcrniiirc iliiit rclicic ilic S W( '( ' li~r :i soi1 io ~lic corrcspwïliiiy 11yilr:itil ic

conclucti~ity-siiçiion hcliiiviotir (Ilrooks iiiid ( 'orcy 1004. I Ii~v~rli;~iiip ci iil. 1077. ;iritl v;iii

(icnuchtcn IOXO). 'I'hc firooks iind ('orcy ( 1904) motlcl is illiisiriitcd Iwc iis ;III cxiiiiiplc.

In this niodcl tiic rcliiiiv~ hydri~ulic contliictivity. A',. o h soil is cxprcsscti as:

&(hJ 1.0 1i)r t i , h l ,

whcrc: & ( h j K(hJ / A',#,, (dimciisionlçss) hydriiiilic conrliicfiviiy (A ' ) ;it ;I iwtiric

. . suçtion haid (h,,) I saturatcd hydriiulic cotiductivity (K,,,,). I hc tiiiiiçrisioiilçss porc-six

distribution indcx, A . can bc iakcn froni thç cxpcrimçntülly dctcrmincd S W U ' :iiitl tIic

K , , viiluc intcrprctcd from thc rcsulis of (i convcniioiiui soil hydniiilic contliiçiivity

(cg. ASTM 1) 2434). lixarnplc curvcs showing the vüri;ition in hydriiulic coriciiiciivity

with suction head are illustrated in Figure 2.3.

The Brooks and Corey mode1 described by Equations 2.4 and 2.5 has been

demonstrated to be accurate for the prediction of the soil-water characteristic curve and

hydraulic conductivity-suction behaviour of sand soils (Brooks and Corey 1964. and

Mualem 1976).

2.4 GEOTEXTILES

Geotextiles are continuous sheets of woven, non-woven or knitted fibres

manufactured from synthetic pol ymer materials (typically polyester or pol ypropy lene).

The sheets are flexible and permeable and generally have the appearancr of a fabric.

Geotextiles are used for separation, filtration, drainage and reinforcement applications in

geotechnical engineering works. Of particular interest to the current study is previous

work related to the unsaturated/saturated hydraulic properties and flow behaviour of

geotextiles in soil.

2.5 HYDRAULIC PROPERTIES OF GEOTEXTILE MATERIALS

2.5.1 Sahrated Hydraulic Properties

The cross-plane saturated hydraulic conductivity of geotextiles can be determined

using r standard permemeter apparatus and the test procedure for geotextiles described

in ASTM D 4491. Typical Km values of woven and non-woven geotextiles range over

several orders of magnitude from 3 to 720 c r n h (Koemer 1998). Due to the

compressibility of geotextiles the flow capacity of a geotextile is ofien calculatrd using

the geotextile permittivity. Y (equivalent to permeability divided by thickness).

Palmeira and Gardoni (2000) studied the influence of vertical confining stress. a.

on the thickness and cross-plane permeahility of the non-woven geotextiles shown in

Table 2.1. Figure 2.Ja illustrates the influence of confining pressure on geotextile

thickness. Similar compressibility data for geotextiles has been reported by Ling et al.

(1991). Palmeira and Gardoni also showed that there was a marked dependcncy of

permeability at normal stresses below a, = 50 kPa. Variation of the saturated cross-plane

permeability of non-woven geotextiles with vertical confining stress is s h o w in Figure

2.4b. Palmeira and Gardoni reported data that showed the differences in the permeability

of geotextile products with the same mass per unit area.

In conventional filter design a geotextile is placed between two soi1 layen with

different particle size distributions and f u l l y - s a ~ t e d conditions are assurned. The

hydraulic properties of the geotextile must be selected to ensure that the geotextile will

permit hydraulic flow across the plane of the geotextile while retaining the upstream soi1

particles and without clogging the geotextile. A conventional rule is that the ratio of the

satwated hydraulic conductivity of the geotextile must be at least equal to the saturated

hydraulic conductivity of the soi1 (k K,OJ(geOmi/e) / KsaJ(so,o 2 1). In critical applications,

the ratio of saturated hydradic conductivities is recommended !O be not less than 10

(Holtz et al. 1997).

Palmeira and Gardoni (2000) also investigated the influence of partial clogging on

the saturated hydrauiic conductivity of non-woven geotextiles. They introduced a

clogging parameter. 5. expressed as the ratio of mass of fines per unit area to the mass per

unit area of geotextile (Ç = MF / MI). From theoretical considerations. the saturated

hydraulic conductivity of a non-woven geotextile would be reduced to zero at a critical

contamination level &,, where:

Here: n = porosity of new geotextile: pl= density of geotextile fibres: and p, = density of

soi1 particles. Typical 5 values as reported by Palmeira and Gardoni from field exhumed

geotextiles ranged from 0.3 to 5.5.

2.5.2 Unsaturated Hydraulic Properties

The unsaturated hydraulic properties of soils have been the subject of a large

amount of research and the behaviour and modeling of unsaturated soils is relatively well

advanced. In contrast, the knowledge of unsaturated hydraulic behaviour of geotextiles is

at a very early stage. The results of the limited research on the topic of unsaturated

hydraulic properties of geotextiles are reviewed in the next sections.

2.5.2.1 Stormont, Henry and Evans (1997)

The fust attempt to measure the water retention function of a geotextile (or

geotextile-water characteristic curve (GWCC) in this thesis) in the cross-plane direction

is reported by Stormont et al. (1997). They determined the GWCCs of four non-woven

polypropylene geotextiles using a rnodified pressure plate apparatus similar to the

equipment developed in the current study (Section 3.4). Each of the four geotextiles

(Table 2.2) was tested in new as well as cleaned conditions. The geotextiles labelled B 1

and B2 are similar to the non-woven geotextiles investigated in this research program.

The cleaned specimens were used to quantiQ the influence of surfactants on the GWCCs.

Surfactants are cornmonly used in the geotextile manufacturing process. The

experimental GWCC results are shown in Figures 2.5 and 2.6. The tests were carried

out from an initial dry condition. followed by wetting-up the geotextile specimen under

decreasing suction heads. The process was revened to determine the drying-path of the

GWCC by reducing the suction head in steps to zero pressure.

The GWCCs for al1 non-woven geotextiles were hysteretic with the drying-paths

showing a higher water content (or degree of saturation) than the wetting-paths at the

same suction head. The sahiration level at a suction head of zero on the wetting-path

ranged from 0.7 to 1 .O for the new geotextile specimens; while for cleaned specimens. the

maximum saturation level was about 0.2. The water-entry suction heads. h,v, for new

non-woven geotextiles fiom pressure plate measurernents ranged from O to 30 mm and

were shown to be similar to the magnitude expected for an uniform coarse sand or pea

gravel. The water-enûy suction head is the maximiun suction that can cause water to

displace air in the pores of the geotextiles. Both new and cleaned geotextiles did not

saturate dong the wetting-path to a suction head of zero. Stormont et al. concluded that

this behaviour was due to the materials being slightly hydrophobie and that positive

pressure heads would likely be required to Mly-saturate the specimens. This behaviour

was more pronounced for the cleaned specimens than the new specimens. However. the

water content of many of the specimens during the initial portion of the drying-path did

not decrease. indicating that once the geotextiles were wetted, a high saturation level was

maintained under srnall suction heads.

No attempt was made by Stormont et ai. to fit a mathematical expression to the

measured GWCC for each geotextile. Additionally. the tests were carried out under a

very low vertical confining pressure (0.78 kPa) which is not representative of a typical

field application.

2.5.2.2 Sfurrnont and Morris (2000)

Stomont and Morris (2000) investigated the influence of the intrusion of soil

particles on the wetting performance of two polyester non-woven geotextiles (Geotextile

A in Table 2.3). Figure 2.7 shows that the intnided soil caused the geotextile specimens

to be wetted-up at higher suction heads (Le. higher water-entry suction head). The water-

entry suction heads for silt and sand-contaminated specimens were not noticeably

different.

In the same paper, the authors reported the results of column infiltration tests

camied out to investigate the influence of a non-woven polypropylene geotextile placed

between dissimikir soils. The infiltration tests were canied out in k e e soil columns.

The first column consisted of silty sand (clmified as SM) with inclusion of a non-woven

polypropylene geotextile (Geotextile B in Table 2.3). The second column replaced the

silty sand layer underneath the geotextile by coarse sand (classified as SP). The final

column consisted of the silty sand layer overlying the coarse sand without a geotextile

inclusion. The three columns were recharged from the top surface at a constant rate and

the suction heads in the soi1 immediately above and below the geotextile were monitored

by tensiometers. From the results of the three column tests. the authon concludrd that

non-woven geotextiles could be expected to substantially impedr flow in unsaturatcd

soils until low values of suction head were reached in the adjacent soil.

2.6 NUMERICAL MODELING OF SANDtSAND-GEOTEXTILE COLUMNS

Bathurst and Knight (1999) reponed the results of a preliminary numerical

investigation of transient water saturation and pore water pressure in soil/soil-geotextilr

columns. The columns were 600 cm high and simulated 1-D surface infiltration Ioading

of soil with and without a single layer inclusion of a woven polypropylene geotextile.

Numerical experiments were carried out using three different soil types. In the soil-

geotextile tests, a single layer inclusion of geotextile (1 mm thick) was placed at about

100 cm below the top of the soil column. Different combinations of soil and geotextile

having a range of cross-plane saturated hydraulic conductivities were simulated under

ponded surface water conditions. A typical medium sand soil with a saturated hydraulic

conductivity of K,, = 414 cmhr was used as the reference soil. The hydraulic behaviour

of the soil was simulated using the Brooks and Corey (1964) mode1 with typical

parameten found in the literature. Progressively finer grained soils were simulated by

decreasing the magnitude of saturated hydraulic conductivity. At the time of the Bathurst

and Knight study, no data was available for the unsaturated hydraulic properties of a

woven geotextile. Hence a range of hydraulic properties for the geotextile confoming to

the Brooks and Corey mode1 were assumed. The numerical simulations were canied out

using the computer program VS2D (Lappala et al. 1987) available from the US

Geological Survey. The following conclusions were made:

1. In order to generate ponding of water above the geotextile in an initially

unsaturated sand column, very large recharge rates were required (Le. recharge

rates that are equa! to or exceed the saturated hydraulic conductivity of the surface

soil).

2. For geotextiles with low air-entry suction heads. ponding c m only occur if the

saturated hydraulic conductivity of the geotextile is many orders of magnitude

lower than the saturated hydraulic conduc tivity of the surrounding soil.

The nurnerical simulations were not calibrated against physical experiments.

Bathurst and Knight recommended that:

1. Physical tests be canied out to determine the water characteristic curves for sand

and woven geotextile matenals.

2. The results of numencal models should be confirmed against instrumented

sand/sand-geotextile column tests.

These research needs have led to the prograrn of expenments and nurnencal

modeling reported in this thesis.

Properties of the non-woven. needle-punched. polypropylene geotextiles investigatrd by Stomont et al. ( 1 997).

Y eC?toxt!!e designation

I 1

Staple fibers

Staple fibers

Continuous filament

Continuous filament

Table 2.3 Properties of the non-woven geotextiles investigated by Stormont and Morris (2000).

Mass per unit areî, 1 Appxentopening MA (g/m2) size, AOS (mm)

Geotexüle desig nation

L

I I I I I I

Thickness b (mm)

Polymer t" Pe

Polyester

Polypropylene

Mass per unit area, MA (g/m2)

Apparent opening size. AOS (mm)

0.04

0.18

Oegree of saturation, S (Sb)

Fipure 2.1 TypicaI soil-water c haracteristic curves (S WCCs) for various soils: ( 1 ) Touchet silt loam; (2) fine sand; (3) glas beads; and (4) volcanic sand (ti.om Fredlund and Rahardjo 1 993).

L - Lebarion Silty Sand -- Pompy Pit Giavelly Sand

SWCCs for typical gravelly and silty sands (from Shoop and Henry 1991).

1 1 O Matric su* @Pa)

Fipure 2.3 Relative hydraulic conductivity as a fûnction of matric suction during drying and wetting cycles of a fine sand soi1 (fiom Brooks and Corey 1964).

Namal stress jkPaj 0.7

O 50 100 150 MO 250 Normal strss [kPa)

Variation of geotextile normal permeability with normal stress for virgin non-woven geotextile specimens: (a) average geoiextile îhickness versus normal stress; (b) noma1 pemeability versus normal stress (fiom Palmeira and Gardoni 2000).

Figure2.5 Wetting and drying-paths of the geotextile-water characteristic curves (GWCCs) for new geotextile specirnens: (a) A l . (b) A2, (c) B 1, and (d) B2 (from Stormont et al. 1997).

Notes: The test resuIts for two specimens from each geotextile type are shown. The arrows denote wetting and drying-pattis.

Figure 2.6 Wetting and drying-paths of the GWCCs for cteaned geotextile specimens: (a) A l , (bj A2, (c) B 1 . and (d) B2 (Frorn Stormont et al. 1997).

Notes: The test results for two specimens from each geotextiIe type are shown. The arrows denote wetting and drying-paths.

1

0,8

0.6 -- -+no soil

0.4 -- +with sand 0.2 -- +with silt

4 with d a y O , 1 +

1 O 100

Suction head (mm)

Fipure 2.7 GWCCs for polyester non-woven geotextiles with intnrded soil (fiom Stormont and Morris 2000).

CHAPTER 3

EXPERiMENiAL DESiGN

3.1 INTRODUCTION

The pnmary objective of the research project was to investigate one-dimensional

(1-D) unsaturatecüsaturated vertical flow behaviour of sand-geotextile layers. The major

part of the experimentai study was a series of 1-D sand/sand-geotextile column tests (i.e.

infiltration tests). A 1-D sand/sand geotextile colurnn test apparatus was designed and

configured to cany out tests simulating surface water infiltration into a sand medium

with and without a single horizontal layer of geotextile inclusion.

In addition, parameters associated with the geotextile and sand specimens were

experimentally determined before carrying out numerical modeling of the sand-geotextile

flow behaviour. Parameters that control the unsaturated~saturated fl ow behaviour of a

sand-geotextile column include the soil-water characteristic curve (SWCC) of the sand

material used in the column test, the geotextile-water characteristic curve (GWCC) of the

selected geotextile, and the thickness of the geotextile under an applied vertical confining

pressure.

The column test apparatus is descnbed first in this chapter followed by

descriptions of the test apparatus used for measuring the SWCC and GWCC. as well as

the equipment for detemining the thickness of the geotextile specimens under an applied

vertical confining pressure.

3.2 ONE-DIMENSIONAL SANDjSAND-GEOTEXTILE COLUMN TESTS

The major expenmental portion of the current study was undertaken using the

215 cm-high instnimented column apparatus s h o w in Figure 3.1. The colurnn test

apparatus was constructed with cylindrical Plexiglas sections with a wall thickness of 0.6

cm (1 1.4 cm outside diameter and 10.2 cm inside diameter). The cylindrical colurnn had

an inside cross-sectional area of 81 cm2. The inside of the column was filled with sand

and constnicted with or without a geotextile inclusion (Le. 1-D sand-geotextile column

test or 1-D sand column test). For sand-geotextile column tests, a single thin layer of

geotextile was placed within the sand at 120 cm below the sand surface. This location

simulated a typical depth for the shailowest layer of a geotextile inclusion in a

conventional reinforced soi1 wall structure. Figure 3.2 shows schematic views of the

column confïgured for a typicai sand-potextile colurnn test.

The top of the column apparatus was designed to provide a constant head of water

to simulate surface recharge of a soi1 mass due to infiltration of ponded water. The

maximum depth of ponded water at the top of the column was restricted to 10 cm in the

study. Hence, for constant head tests, the top boundary condition was equivalent to a

maximum upstream pressure head of 10 cm of water (0.98 kPa). A free water table with

pressure head. h = O was located at 20 cm above the datum and was the constant-head

bottom boundary condition for al1 the column tests. However. this b o u n d q condition

was used for expenmental purposes only and does not imply that a Cree water table may

be expected at this depth behind a retaining wall in the field.

Constant-head infiltration tests on initially unsaturated sand or sand-geotextile

specimens were cmied out using the column test apparatus. During each test the

transient pore-water pressure response and the advancement of the infiltration wetting-

front were monitored using instruments installed through the sides of the column

(Figures 3.1 to 3.3). Details of the instrumentation are described in the following

sections.

3.2.1 Tensiometers

A key objective of the sand/sand-geotextile column tests was to measure the

transient pore-water pressure response in the vicinity of the geotextile inclusion. A total

of nine tensiometers were concentrated at elevations close to the geotextile layer as

shown in Figure 3.2 (denoted by 'T'). The tensiometer elevations are listed in Table

3.1. Each tensiometer was comected to a pressure transducer to measure the transient

pore-water pressure response. The pressure measurement system adopted for the column

tests is referred to herein as a "tensiometer-transducer device". Figure 3.4 shows a

schematic of a tensiometer. The porous cerarnic cup was attached to a brass fitting witii

epoxy resin to ensure a water-tight seal. The bras fitting was attached to a clear PVC

tube (6 mm outside diameter and 3 mm inside diameter) (Figure 3.5) using a screw-type

compression fitting, and the opposite end of the PVC tube was c o ~ e c t e d to a pressure

transducer (Figure 3.6). The entire system was first flushed with carbon dioxide (CO,)

in a sealed container. The CO2 gas was used to facilitate the solution of air bubbles into

the water (Kueper 1999). Thereafier. the porous cup was submerged in de-aired water for

at least 72 hours to ensure that the device was fully-saturated prior to ruming a column

test. The system was inspected to ensure that there was no watrr Icakage.

The tensiometer-transducer device must have a response time of a '*few" seconds

or less in order to measure any rapid change of pore-water pressure (Watson 1965). The

response time is controlled by the pore structure of the porous ceramic cup. A rapid

response irnplies a rapid equilibrium of water pressure between the volume of water

surrounding the tensiometer porous cup and the pores of the cup. The porous ceramic

cup was carefully selected to ensure a satisfactory response tirne. The porous ceramic

cups used in the system were I-bar hi& flow porous ceramic cups purchased from

Soilmoisture Equipment Corp.

3.2.2. Pressure Transducers

Motorola MPX 2100 GP pressure tramducers were used in the tensiometer-

tran3ducer device (Figure 3.6). The pressure transducers can record pore-water pressure

measurements in both positive and negative ranges. The pressure transducers gave an

analog voltage signal that was monitored by a data acquisition system.

3.2.3 Calibration of Tensiometer-Transducer Devices

The response time of the tensiorneter-transducer device was established

independently prior to carrying out the experimental studies. The pressure transducers

were calibrated such that a linear calibration curve was obtained for each device prior to

- conducting the sand~sand-geotextiie coiumn tests. 1 he caiibrarion scheme and the

caiibration results are provided in Appendix A. The tensiometer-transducer devices gave

a response time of less than five seconds based on the results of cdibration tests. Hence,

the tensiometer-transducer device used in the column tests gave essentially a "real-time"

response. In addition, the data in Appendix A shows that each tensiometer-transducer

device gave repeatable pore-water pressure readings.

3.2.4 Conductivity Probes

The location of the infiltration wetting-front in the column tests was determined

using 23 conductivity probes (manufactured in-house) installed along the column

(denoted by "C" in Figure 3.2). The elevation of each conductivity probe is listed in

Table 3.1. A schematic of a conductivity probe is shown in Figure 3.7. Figure 3.8

shows a photograph of the same instrumentation. The conductivity probes were designed

to trigger an abrupt change in DC voltage signal when the wetting-front contacted the

probe wires.

Each conductivity probe consisted of two metal wires (Figure 3.7) connected to

the data acquisition system. The metal wires were separated by approximately 0.5 cm to

create a non-conductive state to an electrical cunent in air. When a continuum of water

bridges the two metal wires, conductivity increases and the change in voltage s ipa l is

used to identiQ the time at which the wetting-front hits the conductivity probe (see

Section 6.2).

3.2.5 Soil Extraction Ports

A total of 23 soil extraction ports were installed dong the column as shown in

Figure 3.2 (denoted by "S"). The elevations of the soil extraction ports are listed in

Table 3.1. Soil specimens were recovered through the soil extraction ports in order to

determine the sand water content at different locations and times dunng the drained

column tests described in Chapter 5.

3.2.6 Data Acquisition System

The pressure transducers and conductivity probes were connected to the HP

3497A data acquisition system shown in Figure 3.9. The measurements fiom the

instrumentation were continuously recorded by the data acquisition system at one second

intervals during the column tests. The data acquisition system was operated by a

personal cornputer (Figure 3.10) with a customized user interface (Figure 3.1 1) and data

storage progarns developed using the HP 3055 data logger software.

3.2.7 Air Channels and Manometers

During each column test. the sand/sand-geotextile column changed from an

unsaturated state to a saturated state. The Richard's Equation (Equation 2.1) and the

Brooks and Corey (1964) mode1 (Equations 2.4 and 2.5) adopted in this investigation do

not consider the behaviour of the air voiume during changes in soii saruration. Aiso. in a

field condition. air which is in communication with the atrnosphere rnust

EXPEIUMENTAL AND NUMERICAL INVESTIGATION · 2005. 2. 11. · The design of soil-geotextile systems...

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