bluuebunny/crossref_metadata_2025 huggingface dataset:
Estimation of Post-Driving Residual Stresses Along Driven Piles in Sand
Authors: Alawneh AS , Husein Malkawi AI
Published: February 2009

Based on both field data collected from engineering literature and measurements made using model piles, a correlation for the residual pressure at the pile tip point is presented. The resulting correlation suggested that pile flexibility is a key parameter controlling the magnitude of the residual point pressure, qres. The calculated residual point pressure values for the database piles using the developed correlation were compared with the measured values and with those calculated using Briaud and Tucker's (1984) method. The comparison indicated that predictions made using the proposed method were closer to the measurements than those obtained using Briaud and Tucker's (1984) method.

In the present study, the residual load distribution along the lower portion of the pile (the bottom 10m) was modeled as a parabola. In the upper portion of the pile, and upon the removal of the driving force, it is assumed that the upward movement of the pile is enough to reverse the direction of the unit shaft resistance from an upward direction during driving to a downward direction, with a magnitude controlled by pile flexibility as well as the available shaft friction along the upper portion of the pile. As a consequence of this approach of modeling residual load distribution, the results indicate that residual load distribution peaks at a distance (less than 0.3L) above the pile tip point. This distance (measured from the pile tip) decreases with increasing pile flexibility, and for flexible pile, residual shear stresses may act in the downward direction all the way down to the pile tip. Also, the method of analysis adopted in this paper indicates that in some cases the magnitude of the peak residual load may exceed 50% of the measured ultimate uplift load. This magnitude is significant and leads to the prudent conclusion that any design method for an axially loaded pile in sand using pile load test data as a database should consider the existence of residual loads when pile load test data are interpreted.
Performance of Drilled Shafts with Isolation Tubes in an Expansive Environment
Authors: Kim M-H , O'Neill MW , Kramer SL
Published: February 2009

An experimental study that included detailed observation of four 305-mm-diameter test shafts, one reference shaft of standard design, and three test shafts with isolation tubes to mitigate skin friction in the vadose zone, is described. The shafts were loaded by naturally expanding and contracting soil over a period of 17 months. The soil at the test site was instrumented to track suction changes to permit development of a computational model predicting soil heave and shrinkage that occur during suction changes at the field site.

Maximum ground movements exceeding 35 mm were observed. Movements of only 1 to 2 mm were observed in the test shafts with isolation tubes, while movements of 4 to 5 mm were observed in the reference shaft. Tension forces in the shafts protected by the isolation tubes were minimal compared to those measured in the reference shaft.

A simple computational model was developed to predict the maximum amount of ground heave based on suction changes. A relationship among suction, total stress, and volumetric strain was obtained for the soil at the test site in the laboratory. This relationship, used as inputs to the predictive model, enabled the computation of the maximum ground heave. Such a model can be used to ascertain whether isolation tubes may be indicated.
A Method for Testing Tensile Strength in Unsaturated Soils
Authors: Tang GX , Graham J
Published: February 2009

This paper presents a new method for testing tensile strength in unsaturated soils. A rigid tensile mold has been designed and simple testing procedures developed. A series of tension tests has been carried out on densely compacted unsaturated soil specimens to evaluate the method. The material tested in this study was a highly plastic 50:50 (by dry weight) mixture of sand and Na-rich bentonite. Cylindrical specimens were the same size and shape as those used for triaxial tests.
Effects of Calcium Sulfate on Swelling Potential of an Expansive Clay
Authors: Azam S , Abduljauwad SN , Al-Shayea NA , Baghabra Al-Amoudi OS
Published: February 2009

The unique chemical features of calcium sulfate are largely manifested by its phase transformation due to the reversible hydration-dehydration reaction. Due to the harsh climatic and environmental conditions in eastern Saudi Arabia, such phase changes add to the potential swelling hazards of local expansive clays. The adsorption of water by expansive soils and the hydration of anhydrite to gypsum are the sources of much damage to foundations throughout the world. This paper attempts to assess the swelling caused by the interaction of calcium sulfate phases, especially gypsum and anhydrite, with expansive clay. Such assessment was primarily based on studying the geotechnical, mineralogical, and volume change characteristics of calcium sulfate-bearing soils. X-ray and thermal analyses were used to estimate the type and amount of minerals during phase transformation of calcium sulfate. The swelling potential was determined using an improved version of the simple odometer and constant-volume tests. The conventional odometer is the device usually used in these tests. However, the size of soil samples, the complete confinement, and the rigidity of the conventional odometer imposes a serious limitation on the application of the laboratory results to actual field problems. Therefore, the authors investigated the use of a large-scale odometer with different mold sizes and shapes on the swelling potential of some mixtures of expansive clay and calcium sulfate phases. In addition, the soil fabric of these mixtures was investigated using scanning electron microscopy to explain the volume change behavior. The results of this investigation indicated that the swelling potential of clay-calcium sulfate mixtures decreased as the percentage of calcium sulfate was increased, and this reduction was more pronounced when gypsum was used. Swelling pressure was observed to be the highest in the conventional odometer and lowest in the large-scale square odometer mold.
New Tool for Shear Wave Velocity Measurements in Model Tests
Authors: Arulnathan R , Boulanger RW , Kutter BL , Sluis WK
Published: February 2009

A method for measuring the shear wave velocity (Vs) of soil in a centrifuge model using a “mini-air hammer” is presented. Propagation of shear waves in a model soil profile was recorded in-flight by a vertical array of four accelerometers placed at different depths. Shear wave velocities were measured at different centrifugal accelerations for Nevada sand and for peaty organic soil. The Vs measured in the centrifuge was in excellent agreement with the Vs measured using piezo-ceramic bender element tests on these soils in a triaxial device. The value of the Vs measurements is demonstrated by typical analysis results for a centrifuge model of horizontally layered peaty organic soil and Nevada sand subjected to simulated earthquake shaking. Site response analyses using the measured shear wave velocities as input parameters produced good agreement with the measured site response.
Tomographic Detection of Low-Velocity Anomalies with Limited Data Sets (Velocity and Attenuation)
Authors: Prada J , Fratta D , Santamarina JC
Published: February 2009

Inherent physical difficulties associated with the effect of low-velocity anomalies on wave propagation, limited data sets, and restricted illumination angles affect the tomographic assessment of piles, caissons, slurry walls, and other similar geotechnical systems. This study evaluates various inversion methodologies for the tomographic detection of low-velocity anomalies. Travel time and amplitude data are gathered in the laboratory by simulating realistic field conditions. The inversion methodology involves data preprocessing, fuzzy logic constraining, and various forms of tomographic inversion based on either pixel or parametric representations of the medium. It is shown that the tradeoff between variance and resolution in pixel-based inversions can be overcome by adding information, such as regularized solutions, or by capturing the problem in parametric form for a presumed simple geometry. Results show that amplitude-based inversion may be more advantageous than time-based inversion in the detection of low-velocity anomalies; however, consistent coupling of transducers is required. The most robust inversion method tested in this study for the detection of low-velocity anomalies under standard field situations (i.e., limited data and restricted illumination angles) involves a combination of fuzzy logic constraining followed by parametric-based inversion.
The Accuracy of Hydrometer Analysis for Fine-Grained Clay Particles
Authors: Lu N , Ristow GH , Likos WJ
Published: February 2009

This paper provides a rigorous analysis on the accuracy of Stokes' equation for calculating particle-size distributions of nonspherical, fine-grained clay particles. Analytical expressions relating the actual particle shape and size to the equivalent “Stokes' diameter” are presented for disk-shaped and rod-shaped particles. Disks and rods are chosen to represent the high aspect ratios typically exhibited by real clay particles. For particle sizes ranging from 0.1 µm to 100 µm and for aspect ratios ranging from 10 to 500, it is shown that Stokes' equation underestimates the maximum particle dimension by up to two orders of magnitude. Consequently, particle-size distributions calculated from conventional hydrometer analysis are shown to be misleading. To confirm the contention that Stokes' equation may not be appropriate for calculating particle sizes and particle-size distributions for fine-grained clays, kaolinite and pulverized mica are characterized by comparing results from hydrometer analysis, sieve analysis, laser diffraction analysis, and scanning electron microscopy (SEM). The experimental results confirm the error estimates from the theoretical evaluation.
The Influence of Variation of Centrifugal Acceleration and Model Container Size on Accuracy of Centrifuge Test
Authors: Zeng X , Lim SL
Published: February 2009

Centrifuge modeling has become a popular and powerful experimental tool in geotechnical engineering. The centrifugal acceleration, which is used to simulate the gravitational acceleration, varies within a model in both magnitude and direction. As a result, the stress field in a centrifuge model is different from that in the prototype being simulated. This paper presents the results of a numerical simulation of the effect of the variation in radial centrifugal acceleration on the stress distribution in a centrifuge model, and its impact on the accuracy of test results. The influence of the centrifuge radius and the size of a model container is investigated.
Determination of Surface Area of Fine-Grained Soils by the Ethylene Glycol Monoethyl Ether (EGME) Method
Authors: Cerato AB , Lutenegger AJ
Published: February 2009

This paper describes a test procedure for determining the total surface area of fine-grained soils using the Ethylene Glycol Monoethyl Ether (EGME). The test involves saturating a soil sample with EGME and then removing the excess EGME in a vacuum desiccator, until the EGME forms a monomolecular layer on the soil surface. The results of the test are expressed as Specific Surface Area (SSA), which describes the surface area/unit mass of dry soil with units of m2/g. Test results are presented demonstrating the effect of various test parameters on the results. Results for a number of different fine-grained soils are presented. A detailed recommended test procedure is given. The proposed method uses simple and inexpensive laboratory equipment, is relatively simple to perform, and allows for rapid determination of SSA.
Factors Affecting the Filter Paper Method for Total and Matric Suction Measurements
Authors: Leong EC , He L , Rahardjo H
Published: February 2009

The filter paper method is used as an indirect means of measuring soil suctions. The advantages of the method include its simplicity, its low cost, and its ability to measure a wide range of suctions. The filter paper method has also been used in the field to measure soil suctions. However, the simplicity of the filter paper method has led to an inadequate understanding of the method and, therefore, improper usage. Recent findings have highlighted the need for more precautions in the use of the filter paper method for suction measurements. This paper presents a literature review of the factors affecting the accuracy of the filter paper method and identifies gaps in the current knowledge of the method. An experimental study was also conducted to clarify some of the factors affecting the response of the two most commonly used filter papers for suction measurements. Whatman No. 42 and Schleicher and Schuell No. 589. Calibration curves of the filter papers show that the water content-suction relationships are different for total and matric suctions. The total suction calibration curve is not very sensitive to applied suctions less than 1000 kPa. The calibration curves obtained for total suction are different from those recommended in ASTM D 5298-94, suggesting that the ASTM D 5298-94 equations should not be used for total suction. Instead of existing bilinear equations, new equations are proposed to describe the total and matric suction calibration curves. All the equations were evaluated using the filter paper method to measure the suction of soil specimens of known matric suctions.
A Laboratory Study of the Hysteresis of a Thermal Conductivity Soil Suction Sensor
Authors: Feng M , Fredlund DG , Shuai F
Published: February 2009

An experimental program was set up to study the capillary hysteresis of the ceramic block for a newly developed thermal conductivity soil suction sensor. The testing program included two series of tests: one series of tests measured the capillary hysteresis of the ceramic blocks and the other measured the hysteresis of the relationships between the suction sensor output and the applied suctions. Test results show that there can be approximately 40% error from the correct suction value if the conventional calibration curve is used without considering the effects of capillary hysteresis. Based on the experimental testing program, a mathematical approach, which is able to take into account the effects of capillary hysteresis, was proposed when interpreting the measured soil suction data.
Interfacial Behavior of Unsaturated Soil with Small-scale Models and Use of Image Processing Techniques
Authors: Gachet P , Klubertanz G , Vulliet L , Laloui L
Published: February 2009

Two small-scale prototypes (physical models) intended to study soil behavior are presented. They allow for 1D and 2D tests on unsaturated soil in a wide range of hydraulic and mechanical boundary conditions. The instrumentation of the testing facilities designed to measure pore water pressures, water fluxes, top displacements, and in-plane displacement fields are detailed. Special attention is devoted to boundary conditions: effects of friction and cohesion at the interface between soil and model on the experimental results and ways to limit their effects are presented. Furthermore, the image processing techniques used to measure in-plane displacements are reviewed. A simple and accurate method based on white light speckle autocorrelation and a marked membrane is proposed.
Effect of Aging on Swelling and Swell-Shrink Behavior of a Compacted Expansive Soil
Authors: Subba Rao KS , Tripathy S
Published: February 2009

Effect of aging on swelling and swell-shrink behavior of a compacted expansive soil is investigated in this paper. An expansive soil having a liquid limit of 100% is used for this purpose. Compacted specimens were prepared and aged for a predetermined number of days (7, 15, 30, and 90 days) to study their swelling and swell-shrink behavior. It has been shown that aging improves the resistance to compression of compacted specimens. The swelling potentials of specimens also decreased with aging. The dominant factors that influence the aging effects are the water content and degree of saturation at the beginning of the aging process. The changed behavior of aged specimens is attributed to particle rear-rangements and formation of bonds, which affect the surface area absorbing water during swelling. The cyclic swell-shrink tests on aged specimens indicated that the differences in vertical displacement during the first swelling were eliminated in the subsequent cycles when specimens were shrunk more, but the aging effect was found to persist with cycles for specimens subjected to lower shrinkage magnitudes.
Ko-Volume Change Characteristics of an Unsaturated Soil with Respect to Various Loading Paths
Authors: Rahardjo H , Fredlund DG
Published: February 2009

The volume change behavior of an unsaturated soil is a function of the stress state variables; namely, net normal stress and matric suction. The total and water volume changes during drained and constant water content loadings are investigated, and their behavior is described with respect to changes in the stress state variables. Volume changes are also presented in terms of void ratio and water content changes. The differing characteristics of volume change during drained and constant water content loadings are reflected clearly through the void ratio and water content changes. The significance of the highest, past matric suction is shown to be similar to the preconsolidation pressure influence on a saturated soil. The laboratory test results show that the water coefficient of volume change changes significantly from the reloading curve to the virgin compression curve. The effect of preconsolidating the soil was also shown to influence significantly the measured soil-water characteristic curve.
Centrifuge Modeling of Tapered Piles in Sand
Authors: Sakr M , Hesham El Naggar M
Published: February 2009

An experimental study was performed to investigate the performance of tapered and cylindrical piles driven into loose sand using the geotechnical centrifuge located at C-CORE, Memorial University, Newfoundland. Twelve open-ended model piles with different configurations, instrumented externally along the shaft, were successfully installed and load tested using the facility. The piles were driven at 1 g, and the loading tests were conducted at 10 g. The paper discusses the design of model piles and details of loading equipment and presents the results of axial compression tests. The results obtained showed that modeling tapered and cylindrical piles with different length-to-diameter ratios was successfully achieved. The external instrumentation technique used in this study proved to be efficient. The surface ronghness effect was found to be important and must be considered when interpreting the test results. The raining technique used in this study produced reasonably uniform soil samples. It was found that as the taper angle increased the shaft resistance increased, and the shaft resistance of the tapered pile was up to 185 % larger than that of the equivalent cylindrical pile. It was also found that the values of the combined shaft resistance factor β for cylindrical piles were consistent with Canadian Foundation Engineering Manual (1992) guidelines. In the case of tapered piles, β values were found to be 80 % higher than those for cylindrical piles, whereas the CFEM design guidelines suggest they should be 30 to 50 % higher. The effect of the taper established from experimental results compared well with the results obtained from an analytical solution based on cavity expansion theory.
Role of Soil Structure and Matric Suction in Collapse of a Compacted Clay Soil
Authors: Rao SM , Revanasiddappa K
Published: February 2009

This paper examines the role of microstructure and matric suction in the collapse behavior of a compacted clay soil from Bangalore District in Karnataka State, India. The microstructure of the compacted specimens was examined by mercury intrusion porosimetry (MIP), and the ASTM Filter Paper Method was used to determine their matric suction. The microstructure and matric suction of the compacted specimens were changed by varying their compaction water content, dry density, and clay content (<2 µm fraction). Experimental results showed that relative abundance of coarse (60 to 6 µm) pores was mainly affected by increasing the dry density of the specimens from 1.49 to 1.77 g/cm3. The relative abundance of coarse and fine (0.01 to 0.002 µm) pores was affected by increasing the compaction water content from 10.6 to 26.4%. Variations in dry density, compaction water content, and clay contents notably affected the matric suction of the compacted specimens. The collapse behavior of the compacted specimens is explained from analysis of the MIP and matric suction results.
Influence of Specimen-Reconstituting Method on the Undrained Response of Sand
Authors: Vaid YP , Sivathayalan S , Stedman D
Published: February 2009

An experimental study aimed at a direct comparison of the undrained behavior of sand using specimens reconstituted by different techniques is presented. It is shown that at identical initial void ratio and effective stress state, the moist-tamped sand is potentially liquefiable, but in the water-deposited state may even be dilative. Water-deposited specimens are shown to be very uniform in contrast to the large nonuniformities that usually occur on moist tamping, rendering their results questionable from the standpoint of laboratory element tests. A direct comparison of the behavior of truly undisturbed sand specimens retrieved by in-situ ground freezing and their corresponding reconstituted counterparts after consolidating to identical initial states is also presented in support of the contention that the fabric that ensues on water pluviation closely simulates that of the natural alluvial and hydraulic fill sands, enabling the use of reconstituted specimens as substitutes for the expensive undisturbed frozen specimens for material characterization.
Influence of Reconsolidation Techniques and Strain Rate on the Stiffness of Undisturbed Clays from Triaxial Tests
Authors: Lo Presti DCF , Pallara O , Cavallaro A , Jamiolkowski M
Published: February 2009

This paper concerns the stiffness assessment of undisturbed clays from triaxial tests. The paper summarizes the research activity undertaken at the authors' universities over the last five years by means of triaxial cells equipped with local gages for axial and radial strain measurements and with piezoceramic bender elements for the measurement of the propagation velocity of differently polarized shear waves. The main purpose of this research was to define reliable test procedures in order to determine the stiffness of geomaterials to be used for settlement analysis under working load conditions. In particular the paper deals with four different topics: (1) evaluation of sample disturbance by means of different methods, (2) assessment of the reconsolidation techniques that minimize the sample disturbance effects, (3) influence of strain rate on the stiffness of undisturbed clays, (4) stiffness anisotropy of undisturbed clays at small strains.
Simplified Seepage Consolidation Test for Soft Sediments
Authors: Sridharan A , Prakash K
Published: February 2009

The consistency of very soft sediments prevents the conventional oedometer test from being applied to study their compressibility and permeability characteristics. The hydraulic consolidation test in existence requires sophisticated instrumentation and testing procedures. The present paper proposes a seepage-force-induced consolidation testing procedure for studying the compressibility and permeability behavior of soft sediments at low effective stress levels. The good agreement that has been observed between the results obtained from the proposed method and the conventional oedometer test at overlapping effective stress levels indicates that the proposed method can be used to study the compressibility and permeability characteristics of soft sediments at low effective stress levels satisfactorily.
Index Properties of Illite-Bentonite Mixtures in Electrolyte Solutions
Authors: Sivapullaiah PV , Savitha S
Published: February 2009

Bentonite, commonly used for liner constructions in waste containment systems, possesses many limitations. Illite or illite containing bentonite has been proposed as an alternative material for liner construction. Their properties in different types of pore fluids are important to assess the long-term performance of the liner. Further, the illite-bentonite interaction occurs and changes their properties. The effect of these interactions is known when the pore fluid is only water. How their properties are modified in electrolyte solutions has been brought out in this paper. The index properties have been studied since they give an indication of their engineering properties. Due to reduction in the thickness of the diffused double layer and consequent particle aggregation in bentonite, the effect of clay-clay interaction reduces in electrolyte solutions. In electrolyte solutions, the liquid limit, the plasticity index, and free swell index of bentonite are lower than illite. The plasticity index of bentonite is further reduced in KCl solution. Clays with a higher plasticity index perform better to retain pollutants and reduce permeability. Hence, the presence of both illite and bentonite ensures better performance of the liner in different fluids.
Applied Research Using a Transparent Material with Hydraulic Properties Similar to Soil
Authors: Welker AL , Bowders JJ , Gilbert RB
Published: February 2009

An innovative material, transparent soil, was used to study flow from a prefabricated vertical drain (PVD). Transparent soil is a mixture of mineral oil, solvent, and amorphous silica. Before using the material to study PVD flow patterns, testing was completed to verify previously published values for hydraulic conductivity and porosity. The results of the independent testing matched the published results well. Experiments using scaled-down and full-size PVDs were completed in cells with diameters ranging from 10.2 to 30.0 cm, respectively. The results of these tests compared favorably to those obtained using an electrical analog and a mathematical model. The transparent soil was an acceptable representation of soil; however, degradations in transparency can be a problem in larger samples. Some other difficulties in using transparent soil, such as finding acceptable sealants and preventing dying of the silica particles, are discussed. In addition, recommended areas of continued research are presented.
Time Domain Reflectometry Development for Use in Geotechnical Engineering
Authors: Siddiqui SI , Drnevich VP , Deschamps RJ
Published: February 2009

This study extends the use of time domain reflectometry (TDR) in geotechnical engineering, a technique originally developed to locate faults in transmission lines. Different elements of the TDR technique are developed, including design of TDR probes, probe installation/test methodology, and relationships between TDR measured dielectric constant and water content of soil. A coaxial probe is developed that is used for measuring the dielectric constant of soil prepared in a cylindrical cell or compaction mold. A multiple-rod field probe is developed that modifies previously developed multiple-rod probes and extends their capability for measuring the in-place dielectric constant of soil. An analytical solution is developed to determine the sampling volume and spatial bias of the TDR measurement. The solution is extended to study the effect of soil disturbance and presence of air gaps due to probe insertion. Experimental results validate the solutions. New relationships are proposed between dielectric constant and water content to eliminate some of the limitations of the existing calibration relationships. Several possible applications of the developed probes, test methodology, and calibration equations for measuring water content and density of soil are illustrated.
Load and Resistance Factor Design (LRFD) for Driven Piles Using Dynamic Methods—A Florida Perspective
Authors: McVay MC , Birgisson B , Zhang L , Perez A , Putcha S
Published: February 2009

The parameters for load and resistance factor design (LRFD) of driven piles using dynamic methods are presented based on a database of 218 pile cases in Florida. Eight dynamic methods were studied: ENR, modified ENR, FDOT, and Gates driving formulas, Case Analysis with Wave Analysis Program (CAPWAP), Case Method for Pile Driving Analyzer (PDA), Paikowsky's energy method, and Sakai's energy method. It was demonstrated that the modern methods based on wave mechanics, such as CAPWAP, PDA, and Paikowsky's energy methods, are roughly twice as cost effective to reach the target reliability indices of 2.0 to 2.5 (failure probability = 0.62 to 2.5%) as the ENR and modified ENR driving formulas. The Gates formula, when used separately on piles with Davisson capacities smaller or larger than 1779 kN, has an accuracy comparable to the modern methods. The utilizable measured Davisson capacity, defined as φ/λ (ratio of resistance/mean capacity) obtained from testing at beginning of redrive (BOR), is only slightly larger than the end of drive (EOD) values. Furthermore, past practice with driving formulas reveals the existence of a large redundancy in pile groups against failure. The latter suggests the use of a lower relatively reliability target index, βT = 2.0 (pf = 2.5%) for single pile design. Also, the utilizable measured Davisson capacity, φ/λ, for all the dynamic methods studied, is quite similar to published values (Lai et al. 1995; Sidi 1985) for static estimates from in situ tests.
A Dynamic Method for Determining the Soil Water Characteristic Curve for Coarse-Grained Soils
Authors: Rassam DW , Williams DJ
Published: February 2009

The air-entry suction is an extremely important parameter in the water characteristic curve, but is difficult to identify when using conventional static methods such as the pressure plate apparatus. In the dynamic method described herein, instantaneous measurement of matric suction and water content are acquired from a soil specimen undergoing a slow drying cycle with the aid of a tensiometer and a soil moisture probe, respectively. The method offers a quick and reliable way of quantifying the drying soil-water characteristic curve (SWCC) for matric suctions of up to 80 kPa. The large number of data points acquired make it easy to obtain an accurate estimate of the air-entry suction. It is particularly effective for soils ranging from medium sands to sandy silts where a nearly continuous SWCC is provided.
A New Technique of Kneading Compaction in the Laboratory
Authors: Kouassi P , Breysse D , Girard H , Poulain D
Published: February 2009

The mechanical behavior of unsaturated compacted soil affects the security of embankments. The aim of compaction methods in the laboratory is to reproduce the compaction effect induced by on-site equipment. This paper summarizes all the results obtained on kneading compaction in order to define a compaction procedure that simulates the action of compacting machines in the field.
Comparison of Internal and Surface Erosion Using Flow Pump Tests on a Sand-Kaolinite Mixture
Authors: Reddi LN , Lee I-M , Bonala MVS
Published: February 2009

The purpose of this paper is to assess the difference between surface and internal erosion processes using results from flow pump tests. Samples of 70% Ottawa sand + 30% kaolinite mixture were used with distilled water and NaCl solutions as permeants. Two kinds of tests were conducted, a surface erosion test where the permeant was pumped through a cylindrical hole of 7-mm diameter and an internal erosion test where the permeant was pumped through intact compacted samples in compaction permeameters. A simple capillary tube model was used to estimate the critical shear stresses needed to cause erosion in surface erosion experiments. It was found that although surface erosion critical shear stresses were exceeded in the intact soil samples, particle clogging in the pores and redeposition of eroded particles prevented mobilization of particles into the effluent stream. Erosion rates estimated using surface erosion parameters were significantly greater than those observed in internal erosion experiments. The results suggest that the fate of eroded particles, including particle redeposition and pore clogging, may govern the internal erosion process far more than the surface erodibility of the soil.
Determination of Thickness of Smooth Geomembranes
Authors: Yesiller N , Cekic A
Published: February 2009

Tests were conducted to determine thickness of smooth, nonreinforced geomembranes using three methods: mechanical (according to ASTM and European standards), ultrasonic, and magnetic methods. The mechanical method is the standard procedure used for determining thickness of geomembranes. The ultrasonic and magnetic methods are not commonly used for geomembranes; however, they are used for testing other materials such as metals. Tests were conducted on 15 geomembranes representing five types of polymers (HDPE, LLDPE, PVC, PP, and EPDM). The results of the testing program indicated that the level of pressures applied affected the thickness measurements in mechanical tests. While the low pressures were not sufficient to flatten particularly the rigid geomembranes, the high pressures tended to compress the geomembranes excessively. Both high and low pressures prevented obtaining representative measurements. The measurements obtained using the ASTM method were more reliable than the measurements obtained with the European method, although it is believed that the most reliable measurements can be obtained by the nondestructive methods (ultrasonic and magnetic). These techniques are sensitive only to the thickness of the materials due to the inherent properties of the test procedures, and they work equally well for rigid and flexible geomembranes. Of the two nondestructive methods, ultrasonic testing is better due to several advantages: it allows for testing from the top surface of geoembranes in the laboratory or in the field, and it can be used on coupons of geomembranes as well as on whole sheets without the need for removing test samples. Both nondestructive methods can be improved for application to geomembranes.
Shear Displacement Dependent Strength of Municipal Solid Waste and Its Major Constituent
Authors: Pelkey SA , Valsangkar AJ , Landva A
Published: February 2009

A limited amount of data exist on the shear strength properties of municipal solid waste. Similar to the soil strength parameters, the data on wastes are reported in terms of a cohesion intercept and an angle of internal friction. Most often the strength parameters reported are for the maximum values mobilized in laboratory testing. Recent state-of-the-art review papers on the topic have summarized the available strength data and noted that large shear displacements are required to mobilize peak shear strength parameters. In comparison, other components of a landfill system such as mineral and geosynthetic liners mobilize peak strengths at much smaller shear displacements. There are, therefore, shear displacement incompatibility issues that need to be resolved. In this paper the shear strength data from the direct shear tests performed on municipal solid waste samples and its major constituent (paper) are presented as a function of shear displacement. Results of a limited number of simple shear tests performed on municipal waste samples are also presented and compared with the data from direct shear testing.
Determination of Specific Gravity and Void Ratio of Pumice Materials
Authors: Wesley LD
Published: February 2009

The vesicular nature and the soft grains of pumice deposits create difficulties in testing them and in interpreting the test results. This note examines the difficulty of measuring specific gravity and estimating void ratio. The difficulty arises from the presence in the particles of a network of internal voids or vesicles, some of which are interconnected and open to the external surface, while others are isolated inside the particle. The void ratio measured by conventional methods invariably includes some of the internal void space, and is therefore, not a true measure of void ratio in terms of the normal definition or understanding of the term. This paper examines different ways of measuring the specific gravity, and the influence of particle size on the results.
Non-Linear Behavior of Lateral-Loaded Pile Taking into Account the Shear Stress at the Sand
Authors: Belkhir S , Mezazigh S , Levacher D
Published: February 2009

Due to recent research advances in understanding mechanisms that govern deep behavior foundations, vertical piles can now be used to correctly support lateral loads.

This paper concerns the development of a computer program for studying non-linear behavior of lateral-loaded piles taking into account the shear stress at the sand.

Some examples issued from the numerical code are compared with experimental results from centrifuge modeling loaded piles tests and with other numerical results from a well-known code used in France.

The influence of shear stress at the soil on the behavior laterally loaded piles was also studied.
Development of Pile Driver and Load Set for Pile Group in Centrifuge
Authors: Pan S , Pu J , Yin K , Liu F
Published: February 2009

When testing piles in a geotechnical centrifuge, it is more efficient to drive piles into the soil in centrifuge flight instead of placing piles prior to running the centrifuge in order to simulate the real conditions. A new pile driver with loading set used to drive and load piles in a centrifuge has been designed and manufactured successfully by the authors. The apparatus on the model container is light and can be maneuvered in the X-Y plane easily. With this apparatus, the piles can be driven or pushed into the soil in centrifuge flight at any position in the X-Y plane. Furthermore, the pile group can be driven into the soil one by one, and the loading test of the pile group can be performed without stopping the operation of the centrifuge.
Ring Shear Tests on a Carbonate Sandy Silt
Authors: Tika TE
Published: February 2009

The paper describes a series of ring shear tests on a carbonate sandy silt designed to simulate soil shearing caused by pile installation and soil shearing resistance developed during pile loading. The tests were performed on the soil and on soil-steel interfaces at large displacements. The soil tests were carried out at constant normal stress conditions, whereas the soil-steel tests were carried out at constant normal stress and constant normal stiffness conditions. The results of the tests are presented and their implications for the behavior of displacement piles are then discussed.
Strength and Deformation Behavior of Soft Bangkok Clay
Authors: Seah TH , Lai KC
Published: February 2009

The influence of stress history and stress state during consolidation and shearing were studied experimentally under undrained triaxial compression and extension modes, by using the Recompression and SHANSEP techniques. In the SHANSEP tests, the samples were consolidated to a vertical consolidation stress of about 1.5 to 2 times of the preconsolidation pressure under Ko consolidation condition, followed by swelling to required overconsolidation ratio before subjecting to undrained shear. Whereas in the Recompression technique, the samples were directly consolidation to in situ effective stress before undrained shearing, the volumetric strains of the reconsolidation were less than 2%, indicating relatively reasonable sampling quality. From the undrained shear results, the Recompression tests give higher undrained shear strength than estimated from SHANSEP tests by about 28%, indicating that some destructuring of soil structure may have occurred in the SHANSEP tests due to large vertical deformation during consolidation. Consequently, the undrained shear strength and the undrained modulus obtained from the SHANSEP tests were much lower.
Shake Table Calibration and Specimen Preparation for Liquefaction Studies in the Centrifuge
Authors: Dief HM , Figueroa JL
Published: February 2009

Recently, a new geotechnical centrifuge was installed at Case Western Reserve University (CWRU). To use this facility in studying soil liquefaction required the development of a feedback correction procedure for the shake table input signals and an appropriate procedure for model preparation, as well as the design of a saturation system setup. These procedures are discussed in detail. Dynamic centrifuge tests at a scale of 60 g's were conducted on scaled pore fluid-saturated models. This fluid is a solution of a water-soluble polymer derived from cellulose at 60 times the viscosity of water. A comparison between the behavior of pore pressure responses during two identical dynamic centrifuge tests using either water or a scaled viscous fluid is documented in this paper.
A New Torsional Shear Device
Authors: d'Onofrio A , Silvestri F , Vinale F
Published: February 2009

Reliable small-strain measurements of deformational characteristics of soils have been one of the challenging aims in geotechnical engineering laboratories over the past decade, in particular when the mechanical behavior of stiff clays and soft rocks has to be analyzed under working conditions.

A new torsional shear apparatus has been developed at the University of Naples, “Federico II,” Italy, suited for accurate and continuous measurement of deformational characteristics at both small strain levels and high stress levels.

In order to accomplish these requirements, the new device incorporates a special electromagnetic loading system designed to apply a maximum torque of more than 5 Nm, and a high-resolution monitoring system, which allows accurate measurements at strain levels below 10−3%. In this paper the design criteria are described in detail, and the efficiency of the new device is shown by several experimental results using a prototype device.
Time-Dependent Stress-Strain Behavior of Soft Hong Kong Marine Deposits
Authors: Zhu J-G , Yin J-H , Luk S-T
Published: February 2009

To investigate the time-dependent stress-strain behavior of Hong Kong marine deposits (HKMD), three types of triaxial tests have been conducted under both compression and extension states. The first is conventional undrained shear tests at different strain rates ranging from 0.0025 to 0.25%/min. The second type is stress relaxation tests. The last type is undrained creep tests. The results are reported in this paper. One order increment of logarithmic strain rate causes about 5 to 9% increase of undrained shear strength. In stress relaxation tests, the pore-water pressure increase is about 10% of the consolidation pressure under extension states. A power law equation is presented to calculate the decay of the deviator stress in relaxation. In multi-stage triaxial creep tests, the log(strain rate)-log(t) relationship of the lower stress level is linear. The slopes of these lines are dependent on current deviator stress as well as stress history.
Instrumentation of an Unsaturated Residual Soil Slope
Authors: Gasmo J , Hritzuk KJ , Rahardjo H , Leong EC
Published: February 2009

The stability of slopes has become a major concern in areas that experience frequent periods of heavy rainfall such as the tropical areas of Southeast Asia. Previous research has indicated that rainfall has a detrimental effect on the stability of residual soil slopes. The reason for this is that the additional shear strength that exists in unsaturated soils due to negative pore-water pressures is lost as a result of rainwater infiltration into the soil.

To study the infiltration characteristics in slopes, a residual soil slope in Singapore was instrumented. The instruments were used to determine the changes in the pore-water pressure distribution throughout the slope in response to evaporation and infiltration. Tensiometers were used to measure negative pore-water pressures, piezometers were used to measure the groundwater level, and a rain gage was used to measure rainfall intensities on the slope. An automated data acquisition system was used to collect the data from the slope. This paper describes the instrumentation program and the procedures associated with the installation of the instruments into the slope. Typical measurement data collected from the slope are presented, and their interpretations are discussed.
Preparation of Epoxy Impregnated Sand Coupons for Image Analysis
Authors: Jang D-J , Frost JD , Park J-Y
Published: February 2009

The study of sand structure using image analysis is an emerging area in soil mechanics research. Quantification of parameters such as the local void ratio distribution or the orientation of sand known to directly affect the behavior of sand masses is possible. However, accurate quantitative measurement requires high-quality specimen coupon surfaces for imaging. A comprehensive procedure for preserving sand specimens with epoxy resin and preparing specimen coupon surfaces for image analysis using a variety of grinding and polishing procedures is presented. Factors affecting the accuracy of subsequent image analysis measurements are discussed. Example images obtained using the proposed procedures are presented to demonstrate their effectiveness and potential.
Interaction Between Hexagonal Wire Mesh Reinforcement and Silty Sand Backfill
Authors: Bergado DT , Teerawattanasuk C , Wongsawanon T , Voottipruex P
Published: February 2009

Pullout tests were conducted on hexagonal wire mesh embedded in silty sand locally known as Ayuttaya sand to investigate the soil reinforcement interaction. Two types of hexagonal wire mesh were tested, namely: (a) galvanized (zinc-coated) which has smaller aperture (cell) dimension of 60 by 80 mm and (b) PVC-coated which has larger aperture (cell) dimension of 80 by 100 mm. The tests were conducted under normal pressures ranging from 35 to 91 kPa and the specimens were pulled at a rate of 1 mm/min. The total pullout resistance of hexagonal wire mesh reinforcement consists of two components, namely; friction and bearing resistance. The bearing resistance is higher than the friction resistance for both types of reinforcement. Higher friction and bearing resistances were obtained with increasing normal pressures. The friction and bearing resistances mobilized on the galvanized wire mesh were greater than the PVC-coated wire mesh, due to higher friction coefficient as well as greater number of transverse and longitudinal members (elements) per unit width in the former than the latter. The proposed analytical method of predicting the pullout resistance and displacement relation using the basic soil and reinforcement properties agreed with the test results reasonably well.
Evaluation of Initial Specimen Condition and Its Effect on Consolidation Properties of Saturated Clay
Authors: Chang M-F
Published: February 2009

The reliability of results of laboratory tests on soils depends on the specimen quality or the initial specimen condition. The quality of specimens prepared using different methods, from clay samples extracted using different techniques and subjected to different periods of storage, can be evaluated based on the measurement of residual porewater pressure. For a laboratory-fabricated normally consolidated clay, the residual porewater pressure decreases when using an inferior sampling technique or preparation method and when the storage time increases, with the effect from the method of specimen preparation dominating. Results of oedometer tests indicate that consolidation properties are noticeably affected by the initial specimen condition, and reasonably strong correlations exist between the preconsolidation pressure and the coefficient of volume compressibility of the clay and the residual porewater pressures in the test specimens. These corrections can be potentially applied to natural clays, although prior verification is necessary.