EXPERIMENTAL AND APPLIED MODELING OF UNSATURATED SOILS
CONTENTS RETENTION PROPERTIES AND COMPRESSIBILITY OF A COMPACTED SOIL MODEL FOR PREDICTION OF SHEAR STRENGTH WITH RESPECT TO DEGREE OF SATURATION SIMPLE MODELING OF STRESS-STRAIN RELATION FOR UNSATURATED SOIL EFFECT OF STRESS PATHS ON SHEAR STRENGTH RESPONSE OF UNSATURATED GASSY SAND FROM HANGZHOU METRO PROJECT A NOVEL SUCTION-CONTROLLED RING SHEAR TESTING APPARATUS FOR UNSATURATED SOILS MODELING UNSATURATED SOIL BEHAVIOR UNDER MULTIAXIAL STRESS PATHS USING A REFINED SUCTION-CONTROLLED CUBICAL TEST CELL EFFECT OF SATURATION ON CYCLIC VOLUMETRIC CHANGE OF COMPACTED SILTY SANDS WETTING AND DRYING UNSATURATED SOIL MOISTURE DIFFUSIVITY PARAMETERS INFLUENCE OF INITIAL WATER CONTENT ON THE COLLAPSIBILITY OF LOESS TREATMENT OF COLLAPSIBLE SOILS BY SALTS USING THE DOUBLE CONSOLIDATION METHOD SOIL WATER CHARACTERISTIC CURVE PARAMETERS OF COMPACTED LATERITIC SOIL TREATED WITH BAGASSE ASH VARIATIONS IN SOIL WATER CHARACTERISTIC CURVES OF LATERITIC SOIL TREATED WITH BENTONITE ANALYTICAL SOLUTION OF THE BARCELONA BASIC MODEL FUNDAMENTALS OF UNSATURATED SOIL MODELLING: HAVE WE GOT IT RIGHT? ELASTOPLASTIC MODELLING OF HYDRAULIC AND MECHANICAL BEHAVIOUR OF UNSATURATED EXPANSIVE SOILS EFFECT OF SLOPE TERRAIN ON DISTRIBUTION OF MATRIC SUCTION IN UNSATURATED SLOPES SUBJECTED TO RAINFALL THREE-DIMENSIONAL SLOPE STABILITY ANALYSIS OF UNSATURATED SOIL SLOPES SUBJECT TO RESERVOIR WATER LEVEL FLUCTUATIONS EFFECT OF ENVIRONMENTAL CONDITIONS ON STABILITY OF AN UNSATURATED SOIL SLOPE FAILURE MECHANISM OF UNSATURATED VOLCANIC SLOPES DUE TO RAINFALL AND FREEZE-THAW ACTIONS CENTRIFUGE MODEL TESTS OF SLOPES WITH WEAK LAYER UNDER RAINFALL DEVELOPMENT OF SHRINKAGE MODEL FOR CLAYS BASED ON MOISTURE VARIATION SLOPE STABILITY ANALYSIS OF RAILWAY EMBANKMENTS CONSIDERING THE EFFECTS OF VEGETATION AND CAPILLARITY STABILIZATION OF EMBANKMENT ON EXPANSIVE SOIL—A CASE STUDY AN EMPIRICAL METHOD FOR PREDICTING FOUNDATION HEAVE RATE IN EXPANSIVE SOIL EFFECT OF WATER SOURCES ON WATER MIGRATION IN THE VADOSE ZONE SIGNAL PROCESSING OF WATER LEVEL FLUCTUATIONS IN A SLOPING SANDY BEACH MODELED IN A LABORATORY WAVE CANAL NON-DESTRUCTIVE MEASUREMENTS OF UNSATURATED SEEPAGE FLOW USING SURFACE GROUND-PENETRATING RADAR UNIFIED SOLUTIONS FOR UNSATURATED SOIL SHEAR STRENGTH AND ACTIVE EARTH PRESSURE RETENTION PROPERTIES AND COMPRESSIBILITY OF A COMPACTED SOIL ABSTRACT: SOIL-WATER RETENTION PROPERTIES AND COMPRESSIBILITY ARE CLOSELY RELATED TO THE STABILITY OF GEOTECHNICAL ENGINEERING STRUCTURES MADE OF COMPACTED SOILS IN THE PRESENT STUDY, THE WATER RETENTION CURVE OF A COMPACTED SOIL FROM NORTHERN FRANCE WAS CHARACTERIZED USING EITHER SUCTION CONTROL METHOD OR SUCTION MEASUREMENT THE RESULTS OBTAINED SHOWED A GOOD CORRESPONDENCE BETWEEN THE TWO METHODS THEN, THESE TWO EXPERIMENTAL METHODS WERE USED IN OEDOMETER COMPRESSION TEST TO HIGHLIGHT THE FACTORS INFLUENCING THE COMPRESSION PROPERTIES, ESPECIALLY IN TERMS OF CHANGES IN COMPRESSION INDEX AS A FUNCTION OF INITIAL SUCTION AND INITIAL STRUCTURE (I E DENSITY) IN THE CASE OF LOW DENSITY (1 1 MG/M3), THE RESULTS EVIDENCED DIFFERENT ZONES FOR THE VARIATIONS OF COMPRESSION INDEX, SEPARATED BY A STRESS THRESHOLD COMPRESSION INDEX DID NOT CHANGE SIGNIFICANTLY WHEN SUCTION VALUES WERE RELATIVELY HIGH AND THE APPLIED VERTICAL STRESSES WERE LOWER THAN THE IDENTIFIED THRESHOLD STRESS INTRODUCTION THE SOIL COMPRESSIBILITY IS HIGHLY VARIABLE BOTH IN TIME AND SPACE BECAUSE IT DEPENDS ON SOIL TYPE (TEXTURE), SOIL STRUCTURE (POROSITY) AND SOIL MOISTURE (SUCTION) TO ENSURE THE STABILITY OF STRUCTURES INVOLVING COMPACTED SOILS, IT IS ESSENTIAL TO UNDERSTAND THE WATER RETENTION PROPERTY AND VOLUME CHANGE BEHAVIOUR OF THE SOILS UNDER THE COMBINED MECHANICAL AND HYDRAULIC EFFECTS MOST OF RESULTS HAVE BEEN OBTAINED FOR SOILS WITH VERY HIGH DRY BULK DENSITIES, AND SHOWED THAT COMPRESSION INDEX DECREASES WITH INCREASING SUCTION BUT FOR SOME LOOSE SOILS SUCH AS COMPACTED SOILS, SOME AUTHORS HAVE FOUND THAT IT DECREASES WITH SUCTION (ZHANG ET AL 1997, DÉFOSSEZ ET AL 2003) WHILE OTHERS HAVE OBSERVED THAT SOIL SUCTION HAS AN INSIGNIFICANT EFFECT (LARSON ET AL 1980, SMITH ET AL 1997, ARVIDSSON AND KELLER 2004, IMHOFF ET AL 2004, MOSADDEGHI ET AL 2006) IN THE PRESENT WORK, THE WATER RETENTION PROPERTIES OF A COMPACTED SOIL TAKEN FROM NORTHERN FRANCE WERE CHARACTERIZED USING EITHER SUCTION CONTROL METHOD OR SUCTION MEASUREMENT OSMOTIC SUCTION CONTROL METHOD WAS USED FOR THE DESICCATION PATH AND SUCTION MEASUREMENT USING HIGH CAPACITY TENSIOMETER WAS APPLIED FOR THE HUMIDIFICATION PATH THEN, THESE TWO EXPERIMENTAL METHODS WERE USED IN OEDOMETER COMPRESSION TEST TO INVESTIGATE THE SUCTION EFFECT ON THE COMPRESSION PROPERTIES MATERIALS FOR THIS STUDY, A COMPACTED LOAMY SOIL (17 3% CLAY, 77 7% SILT, 5% SAND) FROM A SITE AT MONS IN NORTHERN FRANCE WAS USED THE SOIL HAS A LIQUID LIMIT OF 29%, A PLASTICITY INDEX OF 6 AND A SOLID DENSITY OF 2 7 MG/M3 AIR-DRIED SOIL WAS PASSED THROUGH 2 MM SIEVE THE WATER CONTENT OF THE SOIL POWDER IS 2% TESTING EQUIPMENT AND PROCEDURE SUCTION CONTROL METHOD THE OSMOTIC TECHNIQUE FOR SUCTION CONTROL TESTING IS BASED ON THE USE OF A CELLULOSE SEMI-PERMEABLE MEMBRANE AND AN AQUEOUS SOLUTION OF ORGANIC POLYETHYLENE GLYCOL (PEG) MOLECULES WHEN THE SOIL IS SEPARATED FROM THE PEG SOLUTION BY THE MEMBRANE, WATER CAN CROSS THE MEMBRANE WHEREAS THE PEG MOLECULES IN SOLUTION CANNOT DUE TO THEIR LARGE SIZE THE WATER STOPS FLOWING ONCE EQUILIBRIUM STATE IS REACHED; THERE IS THUS THE SAME SUCTION IN THE PEG SOLUTION AND THE SOIL THIS SUCTION IS KNOWN FROM THE PEG CALIBRATION CURVE ACCORDING TO DELAGE ET AL (1998) AND DELAGE AND CUI (2000), THERE IS A UNIQUE RELATIONSHIP BETWEEN PEG CONCENTRATION, C (G PEG/G WATER) AND SUCTION, S (MPA), INDEPENDENT OF THE MOLECULAR WEIGHT OF THE PEG OEDOMETER COMPRESSION TESTS WERE CONDUCTED WITH SUCTION STATE CONTROLLED USING THE OSMOTIC TECHNIQUE TO STUDY THE COMPRESSION INDEX A STANDARD OEDOMETER WAS ADAPTED TO THE OSMOTIC TECHNIQUE, ALLOWING COMPRESSION TESTS AT CONTROLLED SUCTION FIGURE 1 SHOWS THE OSMOTIC-BASED OEDOMETER EMPLOYED THE CELL BASE WAS GROOVED TO HOMOGENIZE THE DISTRIBUTION OF THE PEG SOLUTION; A FINE SIEVE WAS PLACED OVER THE GROOVES TO PROTECT THE SEMI-PERMEABLE MEMBRANE PLACED BETWEEN THE SIEVE AND THE SOIL SAMPLE A CLOSED CIRCUIT ACTIVATED BY A PERISTALTIC PUMP WAS DESIGNED TO CIRCULATE THE PEG SOLUTION A ONE-LITRE BOTTLE WAS USED TO ENSURE A QUASI-CONSTANT CONCENTRATION IN SPITE OF WATER EXCHANGES WITH THE SOIL SAMPLE A CAPILLARY TUBE PLACED ON THE SEALED BOTTLE ALLOWED MONITORING WATER EXCHANGES BETWEEN THE PEG SOLUTION AND THE SOIL SAMPLE THE BOTTLE WAS PLACED IN A THERMOSTATIC WATER BATH AT 20±0 5°C TO AVOID ANY TEMPERATURE EFFECTS ON THE WATER EXCHANGE MEASUREMENTS IN ADDITION, THE ENTIRE SYSTEM WAS INSTALLED IN AN AIR-CONDITIONED ROOM (20±1°C) IN ORDER TO QUANTIFY THE CHANGE OF WATER VOLUME DUE TO TEMPERATURE AND EVAPORATION, A SECOND BOTTLE FULL OF PEG SOLUTION WITH A CAPILLARY TUBE WAS PLACED IN THE WATER BATH EXPERIMENTAL AND APPLIED MODELING OF UNSATURATED SOILS FIGURE 1 SCHEMATIC OF OSMOTIC OEDOMETER AND ACTUAL PICTURE SERIES I: FOR EACH SAMPLE PREPARATION, 103 62 ± 0 05 G DRY POWDER WAS USED THE SOIL POWDER WAS HUMIDIFIED BY PULVERIZATION TO REACH 12 5% WATER CONTENT; THE SAMPLE WAS PREPARED BY COMPACTION IN THE OEDOMETER CELL TO REACH DIMENSIONS OF 70 MM IN DIAMETER AND 24 MM HIGH, WITH A DRY BULK DENSITY OF 1 1 MG M-3 THE INITIAL SUCTION OF THE COMPACTED SAMPLE BEFORE COMPRESSION TEST WAS ABOUT 200 KPA, ESTIMATED BY THE TENSIOMETER CONSIDERED IN THE OTHER EXPERIMENTAL METHOD: SUCTION MEASUREMENT SERIES II: TEST SAMPLES WERE PREPARED AT DIFFERENT INITIAL WATER CONTENT WI = 12 5, 13, 16 AND 25% WHICH SUPPLY THE INITIAL SUCTIONS NEAR TO 200, 100, 50 AND 10 KPA SEPARATELY FOR THE SERIES I, THE SIX COMPRESSION TESTS WERE PERFORMED AT DIFFERENT SUCTIONS: 0, 10, 50, 100, 180 AND 200 KPA, EACH TEST HAVING BEEN STARTED WITH A SUCTION APPLICATION PROCESS UNDER ZERO VERTICAL STRESS THE SUCTION WAS APPLIED EITHER BY CIRCULATING PEG SOLUTION OF THE DESIRED CONCENTRATION OR PURE WATER (FOR ZERO SUCTION) EQUILIBRIUM WAS INDICATED BY STABILIZATION OF THE SOLUTION LEVEL IN THE CAPILLARY TUBE, PUMP PEG PEG WATER BATH SOIL VERTICAL STRESS SEMI - PERMEABLE MEMBRANE CAPILLARY TUBE CONTROL OF WATER EXCHANGE EXPERIMENTAL AND APPLIED MODELING OF UNSATURATED SOILS WHEN THERE WAS NO CHANGE IN VARIATION OF WATER VOLUME IN THE CAPILLARY TUBE OR IN THE SOIL IT WAS OBSERVED THAT EQUILIBRIUM TIME DEPENDED ON THE AMPLITUDE OF SUCTION CHANGES: THREE DAYS FOR 200 KPA AND 18 DAYS FOR ZERO SUCTION FOR THE SERIES II, PEG SOLUTIONS PROVIDED SEPARATELY SUCTIONS OF 10, 50,100 OR 200 KPA FOR THE FOUR SAMPLES WITH DIFFERENT INITIAL WATER CONTENT THE EQUILIBRIUM TIME WAS 1 DAY FOR THESE SAMPLES COMPRESSION WAS PERFORMED UNDER CONSTANT SUCTION CONDITION BY STEP-LOADING USING A PNEUMATIC SYSTEM: 10-20-50-100-200-400-800 KPA LOADING TIME OF EACH STRESS WAS FUNCTION OF TIME NEEDED TO REACH SUCTION EQUILIBRIUM AGAIN (ABOUT 40 MIN FOR EACH STEP) THE DISPLACEMENT STABILIZATION WAS CONTROLLED BY TWO SENSORS (ACCURACY OF 0 01 MM) SYMMETRICALLY INSTALLED ON BOTH SIDES OF THE OEDOMETER CELL LOADING TIME TOOK UNLOADING WAS CARRIED OUT FOLLOWING THE SAME STRESS STEPS UNTIL 50 KPA THE FINAL WATER CONTENT WAS DETERMINED BY OVEN-DRYING AT 105°C FOR 24 HOURS SUCTION MEASUREMENTS THE SUCTION OF SOIL SPECIMENS WAS MEASURED USING A TENSIOMETER INSERTED THROUGH AN OPENING IN THE BASE PEDESTAL IN A STANDARD 70 MM DIAMETER OEDOMETER, AS SHOWN IN FIGURE 2 THE SAMPLE WAS PLACED INSIDE THE OEDOMETER IN CONTACT WITH THE TENSIOMETER, THEN COVERED BY A LOAD CAP TO ENABLE VERTICAL LOADING BY THE PISTON A NEOPRENE MEMBRANE WAS USED TO COVER THE SOIL AND CAP IN ORDER TO AVOID ANY EVAPORATION THAT COULD CAUSE INCREASE OF SOIL SUCTION THE PORE-WATER PRESSURE UW MEASURED WITH THE TENSIOMETER CORRESPONDS TO THE SOIL SUCTIONS THE TENSIOMETER USED (FIGURE 3) IS OF IMPERIAL COLLEGE TYPE, WHICH HAS BEEN SUCCESSFULLY USED IN PERFORMING SUCTION MEASUREMENTS UNDER LABORATORY CONDITIONS (DINEEN AND BURLAND 1995, RIDLEY AND BURLAND 1996, TARANTINO ET AL 2000, TARANTINO AND MONGIOVÌ 2001, 2002, RIDLEY ET AL 2003) IT HAS PROVIDED EXCELLENT PERFORMANCE IN TERMS OF ACCURACY, MEASUREMENT DURATION AND OPERATING TENSION RANGE (0-1 5 MPA: TARANTINO AND MONGIOVÌ 2001) IT WAS USED BY CUI ET AL (2007) TO MONITOR FIELD SUCTION CHANGES THE TENSIOMETER CONSISTS OF A POROUS CERAMIC STONE WITH A 1 5 MPA AIR ENTRY VALUE, A WATER RESERVOIR 0 1 MM THICK AND A STRAIN GAUGE ATTACHED TO THE DIAPHRAGM PLATE SOIL SAMPLES WERE PREPARED BY COMPACTING SOIL FRAGMENTS < 2MM WHICH WERE RE-WETTED AT DIFFERENT INITIAL WATER CONTENTS, WI = 12 5, 14 3, 16, 19 8 AND 25%, BY WATER SPRAYING THE SAME MASS OF DRY SOIL WAS USED FOR ALL SAMPLES (103 62 ± 0 05 G) INITIAL COMPACTION WAS CARRIED OUT DIRECTLY IN AN OEDOMETER TO PREPARE SOIL SAMPLES THE FINAL DIMENSIONS OF THE SOIL SAMPLES WERE: DIAMETER 70 MM; HEIGHT 24 MM; CORRESPONDING TO A BULK DRY DENSITY OF 1 1 MG M-3 AFTER PRODUCING THE SOIL SAMPLE, VERTICAL STRESSES OF 10, 20, 50, 100, 200, AND 800 KPA WERE APPLIED STEP BY STEP USING A CONTROLLED PNEUMATIC SYSTEM UNLOADING WAS CARRIED OUT FOLLOWING THE SAME STRESS STEPS UNTIL 50 KPA TESTS WERE PERFORMED UNDER UNDRAINED CONDITIONS FOR WATER PHASE THE VERTICAL DISPLACEMENT WAS RECORDED USING TWO TRANSDUCERS (ACCURACY OF 0 01 MM) INSTALLED SYMMETRICALLY (FIGURE 2) THE FINAL WATER CONTENT WAS DETERMINED BY OVEN-DRYING AT 105°C FOR 24 H DURING LOADING AND UNLOADING, SUCTION CHANGES WERE CONTINUOUSLY MONITORED BY THE TENSIOMETER INSTALLED ON THE OEDOMETER THREE COMPRESSION TESTS WERE PERFORMED FOR EACH INITIAL WATER CONTENT CONDITIONS EXPERIMENTAL AND APPLIED MODELING OF UNSATURATED SOILS FIGURE 2 OEDOMETER EQUIPPED WITH TENSIOMETER FOR SUCTION MONITORING (SCHEMATIC LAYOUT OF THE NEOPRENE MEMBRANE COVERING THE OEDOMETER CELL: AN AIR POCKET OF 15 MM HIGH IS PROVIDED BETWEEN THE MEMBRANE AND THE CELL ) FIGURE 3 SCHEMATIC OF IMPERIAL COLLEGE TYPE TENSIOMETER RESULTS AND DISCUSSION FIGURE 4 PRESENTS THE WATER RETENTION CURVE OBTAINED USING THE OSMOTIQUE TECHNIQUE (SERIES I) AND TENSIOMETER IN THE LOW SUCTION RANGE OF 0-200 KPA CONTINUOUS SUCTIONS DECREASE IS OBSERVED WITH INCREASING WATER CONTENT THE RESULTS OBTAINED SHOWED A GOOD CORRESPONDENCE BETWEEN THE TWO METHODS BLACK MEMBRANE DISPLACEMENT LOAD TRANSDUCERS PISTON LOAD CAP OEDOMETER AND SOIL SAMPLE LOAD PISTON BLACK MEMBRANE 1 5 CM LOAD CAP SOIL SPECIMEN BASE PEDESTAL TENSIOMETER POROUS STONE SEAL DIAPHRAGM STRAIN GAUGE WATER RESERVOIR ARALADITE ELECTRICAL CONNECTION EXPERIMENTAL AND APPLIED MODELING OF UNSATURATED SOILS