expeiumental and numerical investigation · 2005. 2. 11. · the design of soil-geotextile systems...
TRANSCRIPT
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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
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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.
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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.
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................................................................................ ABSTRACT.. .............................................................. ACKNOWLEDGEMENTS..
........................................... .............. TABLE OF CONTENTS.. ,...... LlST OF
LlST OF
LlST OF
LIST OF
LlST OF
TABLES ................. .... ................................................. FIGURES ................... ......a................. NOTATIONS.. ...................................................................
............................................................. ABBREVl ATlONS .............................................................. CONVERSIONS..
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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
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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 .................................................................
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...... 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
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...................................... 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 ...............................................................
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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 .........................
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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
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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
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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
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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
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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
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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
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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
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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
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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..
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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
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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
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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
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Figure 6.12 Transient pore-water pressure responses at elevation of 90 cm
above datum and 5 cm below the geotextile layer (T7) ........... 129
Figure 6.13 Transient pore-water pressure responses at elevation of 87 cm
above datum and 8 cm below the geotextile layer (T8).. ......... 130
Figure 6.14 Transient pore-water pressure responses at elevation of 83 cm
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
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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
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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
Figure 7.14 Transient pore-water pressure response at depth of 11 1 cm
(T5) for experimental and numerical sand column tests (Test
1) ....................................................................... 164
Figure 7.15 Transient pore-water pressure response at depth of 116 cm
(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
Figure 7.18 Transient pore-water pressure response at depth of 101 cm
(T3) for experimental and nurnencal sand-geotextile column
tests (Test 2). .. ... ...................................................... 1 66
-
Figure 7.19 Transient pore-water pressure response at depth of 106 cm
(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
Figure 7.21 Transient pore-water pressure response at depth of 116 cm
(T6) for expenmental and numerical sand-geotextile column
tests (Test 2).. .......................................................... 167
Figure 7.22 Transient pore-water pressure response at depth of 10 1 cm
(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
Figure 7.24 Transient pore-water pressure response at depth of 101 cm
(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
-
Figure 7.26 Transient pore-water pressure response at depth of 10 1 cm
(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
Figure 7.30 Original and adjusted hydraulic conductivity curves for the
contaminated woven geotextile.. .................................. 1 72
Figure 7.31 Original and adjusted hydraulic conductivity curves for the
new non-woven geotextile.. ......................................... 173
Figure 7.32 Original and adjusted hydraulic conductivity curves for the
.. 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
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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
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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)
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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)
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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
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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.
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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
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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
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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
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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
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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
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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.
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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
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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).
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L - Lebarion Silty Sand -- Pompy Pit Giavelly Sand
SWCCs for typical gravelly and silty sands (from Shoop and Henry 1991).
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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).
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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).
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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.
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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.
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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).
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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.
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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
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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
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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.
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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.
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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