Journal of Geotechnical and Geoenvironmental Engineering

Published by American Society of Civil Engineers
Online ISSN: 1090-0241
Publications
Article
A series of biaxial (plane strain) experiments were conducted on three sands under low (15 kPa) and high (100 kPa) confining pressure conditions to investigate the effects of specimen density, confining pressure, and sand grain size and shape on the constitutive and stability behavior of granular materials. The three sands used in the experiments were fine-, medium-, and coarse-grained uniform silica sands with rounded, subangular, and angular grains, respectively. Specimen deformation was readily monitored and analyzed with the help of a grid pattern imprinted on the latex membrane. The overall stress-strain behavior is strongly dependent on the specimen density, confining pressure, sand grain texture, and the resulting failure mode(s). That became evident in different degrees of softening responses at various axial strains. The relationship between the constitutive behavior and the specimens' modes of instability is presented. The failure in all specimens was characterized by two distinct and opposite shear bands. It was found that the measured dilatancy angles increase as the sand grains' angularities and sizes increase. The measured shear band inclination angles are also presented and compared with classical Coulomb and Roscoe solutions.
 
Article
Numerical studies were conducted to improve the understanding of the behavior of geosynthetic-reinforced column-supported embankments. Due to the complexity of the problem, so far, consolidation process and three-dimensional patterns of columns have not been well simulated in most published numerical studies. As a result, the time-dependant behavior and the serviceability of this system have not been well evaluated. In this study, a three-dimensional coupled mechanical and hydraulic modeling was conducted using FLAC3D to consider consolidation and three-dimensional arrangement of columns. This study was based on a well-documented bridge approach embankment reinforced by a layer of geotextile and supported by deep mixed (DM) columns. The foundation soils including soft clay and silt, the embankment fill, and the deep mixed columns were modeled as linearly elastic-perfectly plastic materials with Mohr–Coulomb failure criteria. The geotextile reinforcement was simulated by geogrid elements incorporated in the FLAC3D software, which can sustain in-plane tensile force only. The staged construction was simulated by building the embankment in lifts. The duration of each lift was the same as the actual construction time plus the lapse time between two consecutive stages. The development of settlement and tension in the geotextile with time is compared with the long-term monitoring data and yields good agreement. The generation and dissipation of excess pore water pressure during and after construction are presented and discussed.
 
Article
This paper presents the multiaxial formulation of a plasticity model for sand under cyclic shearing. The model adopts a kinematic hardening circular cone as the yield surface and three non-circular conical surfaces corresponding to the deviatoric stress ratios at phase transformation, peak strength and critical state. The shape of the non-circular surfaces is formulated in accordance with the experimentally established failure criteria, while their size is related to the value of the state parameter ψ. To simulate cyclic response under small and large shear strain amplitudes without a change in model parameters, it was found necessary to introduce: (a) a non-linear hysteretic (Ramberg–Osgood type) formulation for the strain rate of elastic states and (b) an empirical index of the effect of fabric evolution during shearing which scales the plastic modulus. This index is estimated in terms of a macroscopic second-order fabric tensor, which develops as a function of the plastic volumetric strain increment and the loading direction in the deviatoric plane. Comparison of simulations to pertinent data from 27 resonant column, cyclic triaxial and cyclic direct simple shear tests provide a measure for the overall accuracy of the model.
 
Article
: This paper is concerned with the problem of soil amplification and structural damage due to local site conditions in sedimentary valleys during earthquakes. It focuses on a small valley in Kirovakan, for which one dimensional (1D) wave propagation analyses have failed to provide adequate answers for the large extent and spatial distribution of damage during the 1988 Armenia Earthquake. A more realistic two-dimensional finite element analysis is performed herein in search of an explanation for the observed behavior. Using as input an inferred rock accelerogram, the response of the valley is calculated for a vertically incident SH-wave. Synthetic accelerograms of the surface ground motion are presented for different sites; these accelerograms are then used to determine the amplification ratios of the surface response with respect to that of the free-field motion of the rock outcrop, for different frequencies and for a continuous set of sites. In addition, response spectra are evaluated...
 
Article
This paper presents a complete methodology for both probabilistic and deterministic assessment of seismic soil liquefaction triggering potential based on the cone penetration test (CPT). A comprehensive worldwide set of CPT-based liquefaction field case histories were compiled and back analyzed, and the data then used to develop probabilistic triggering correlations. Issues investigated in this study include improved normalization of CPT resistance measurements for the influence of effective overburden stress, and adjustment to CPT tip resistance for the potential influence of "thin" liquefiable layers. The effects of soil type and soil character (i.e., "fines" adjustment) for the new correlations are based on a combination of CPT tip and sleeve resistance. To quantify probability for performance-based engineering applications, Bayesian "regression" methods were used, and the uncertainties of all variables comprising both the seismic demand and the liquefaction resistance were estimated and included in the analysis. The resulting correlations were developed using a Bayesian framework and are presented in both probabilistic and deterministic formats. The results are compared to previous probabilistic and deterministic correlations.
 
Article
The failure of the levee and floodwall section on the east bank of the 17th Street drainage canal was one of the most catastrophic breaches that occurred during Hurricane Katrina. It produced a breach that rapidly scoured a flow pathway below sea level, so that after the storm surge had largely subsided, floodwaters still continued to stream in through this breach for the next two and a half days. This particular failure contributed massively to the overall flooding of the Metropolitan Orleans East Bank protected basin. Slightly more than half of the loss of life, and a similar fraction of the overall damages, occurred in this heavily populated basin. There are a number of important geotechnical and geoforensic lessons associated with this failure. Accordingly, this paper is dedicated solely to investigating this single failure. Geological and geotechnical details, such as a thin layer of sensitive clay that was laid down by a previous hurricane, proper strength characterization of soils at and beyond the toe of the levee, and recognition of a water-filled gap on the inboard side of the sheet pile cutoff wall are judged to be among the most critical factors in understanding this failure. The lessons learned from this study are of importance for similar flood protection systems throughout other regions of the United States and the world.
 
Article
This paper examines immediate and time-dependent compression of tire derived aggregate (TDA)and TDA-soil composites. To accommodate large particle sizes, modified experimental devices were developed and used to test tire chips and tire shreds. Immediate compression of TDA, which results almost entirely from the reduction of pore volume, increases with TDA content and tire particle size. The secant constrained modulus (Msec ) of TDA defined over the stress range of 0–50 kPa varied from a low of 255 kPa (100% tire shreds )to a high of 1,320 kPa (50% tire chips). A characteristic relationship between strain and time exists for TDA and TDA composites under one-dimensional confined compression. Time-dependent deformation is well described by the modified secondary compression index (Cae) which ranged from 0.0010 (50% tire chips) to 0.0074 (100% tire chips). Time-dependent deformation was inversely proportional to sand content, with the most significant changes resulting from the addition of 15% sand. Both applied stress and tire particle size appear to have a negligible effect on time-dependent compression of TDA. Based on the findings of this study it is recommended that practitioners assess time-dependent settlement when designing a TDA structure and if necessary incorporate design features to accommodate these settlements.
 
Article
This research study deals with the characterization of two-phase flow in a fractured rock mass. A comprehensive mathematical model with which to predict the quantity of each flow component in a single joint is developed. A joint with two parallel walls filled with layers of water and air (stratified) is analyzed. The effects of mechanical deformation of the joint, the compressibility of fluids, the solubility of air in water, and the phase change between fluids have been taken into account to develop analytical expressions which describe the behavior at the air–water interface. The model was calibrated using a newly designed two-phase (high-pressure) triaxial cell. Tests were conducted on fractured hard rock samples for different confining pressures with inlet water and inlet air pressures. As in single-phase flow, it was found both experimentally and theoretically, that the flow quantities of each phase decreases considerably with an increase in confining stress. The results also confirm that the effect of joint deformation and compressibility of fluids governs the flow volume of two-phase flow. Good agreement was obtained between the experimental data and numerical predictions.
 
Article
This study highlights a mathematical (analytical) model simulation the filtration phenomenon applicable to a base soil-filter system, incorporating the hydraulic conditions and the relevant material properties such as porosity, density, friction angle, and the shape and distribution of particles. The model is founded on the concept of critical hydraulic gradient derived from limit equilibrium considerations, where the migration of particles is assumed to occur under applied hydraulic gradients exceeding this critical value. The raate of particle erosion, and hence, the filter effectiveness is quantified on the basis of mass and momentum conservation theories. By dividing the base soil and filter domains into discrete elements, the model is capable of predicting the time-dependent particle gradation and permeability of each element, thereby the amount of material eroded from or retained within the system. Laboratory tests conducted on a fine base material verify the validity of the model. The model predictions are also compared with the available empirical recommendations, including the conventional grading ratios.
 
Article
This paper presents the use of the trial load method and the block element method with elastoviscoplastic discontinuities for analysis of arch dams. The arch dam is considered as an arch-cantilever system and the foundation as a block element system. With the displacement compatibility condition at the contact surface of the dam and the foundation (including abutment), the governing equations of the arch dam and foundation are established. These methods are used for the analysis of the double curvature arch dam with complex geology conditions of the Xiaowan Hydroelectric Project in China. The deformation and stress states in both the dam body and the foundation are determined. Furthermore, the stability safety factors of the foundation and the abutment are calculated at the same time, which allows for an optimal design of the arch dam considering the strength, the deformation and the stability of the dam and foundation.
 
Schematic of Soil Structure and Oxygen Transport in Pyrite Oxidation Model: (a) Soil Profile; (b) Oxygen Transport Down Macropores and into Pyritic Clay Matrix  
Analytical and Numerical Values for T 
Measured and Simulated Pyrite Concentrations 
Schematic of FEMWATER Mesh: (a) Side Elevation View Showing Boundary Conditions and Initial Ground-Water Level; (b) Plan View Showing Triangular Element Geometry and Nodes  
Article
A theoretical approach for calculating pyrite oxidation in acid sulfate soil with a macropore/matrix structure is described. This approach accounts for vertical oxygen transport through soil macropores and the subsequent lateral diffusion of oxygen into the soil matrix. As oxygen is supplied into the matrix, it is consumed by pyrite and other oxygen-consuming processes. A numerical solution to the theoretical model was developed and used in the computer simulation model ACID3D. The numerical approach is based on a linear relationship between oxygen consumption and dissolved oxygen concentration. The numerical scheme is shown to be in good agreement with the analytical solutions. ACID3D was used in conjunction with a commercially available saturated/unsaturated water flow model to assess the effectiveness of a ground-water management strategy to minimize acid generation caused by pyrite oxidation currently being carried out on a trial site on the south coast of New South Wales, Australia.
 
Article
Unsaturated drainage layers (UDLs) have been demonstrated to greatly increase the lateral diversion capacity of capillary barriers. The inclusion of a UDL allows native soils suitable for vegetation growth to be used as the finer soil as lateral drainage properties of the layer no longer need to be considered. A comprehensive numerical study was conducted to investigate the influence of the interface slope and the UDL material on the system's ability to laterally divert downward moving moisture. A capillary barrier system with and without a UDL was simulated for 10 years using daily varying climatic data for three locations in the United States. Three different sands were simulated as the UDL and were modeled at slopes of 5, 10, and 20%. The numerical results confirm that the inclusion of an unsaturated drainage layer at the fine/coarse interface of a capillary barrier can provide significant improvements in the performance of the cover system by laterally draining water. This improvement in performance may allow the system to be successfully implemented in climates wetter than previously were thought suitable. The diversion length (the distance water is diverted laterally with no downward flow through the fine/coarse interface) of a capillary barrier with a UDL was found to be proportional to the slope of the fine/coarse interface. In addition, a relationship between lateral diversion lengths in a capillary barrier and the UDL material was developed and found to be dependent on the unsaturated flow characteristics of the UDL. These relationships allow the performance of a variety capillary barrier UDL designs to be calculated knowing the behavior of one system for a given location.
 
Article
In effective filters, potentially erodible base particles are transported to the filter and retained to form a stable self-filtration layer. At any given time, the mass proportion of the filter and the base materials in this layer depends on the initial porosity of the filter and the subsequent porosity of the self-filtration layer. In this paper, an analytical procedure is given to obtain the particle size distribution (PSD) of the self-filtration layer by combining the PSDs of the filter and the base soil modified by Dc95, where 95% of filter constrictions are finer than the size denoted by Dc95. The assessment of internal stability of the PSD of the self-filtration layer forms a rational model to successfully identify the effective filters from their ineffective counterparts. The proposed model is verified by large-scale laboratory tests carried out by the writers in addition to other published data. The model performance is acceptable in relation to various base and filter materials, and provides an alternative and rigorous design approach by eliminating most limitations of the conventional particle based criteria (e.g., D15/d85 ratio).
 
Geometrical Properties of Coarse Soils
Geometrical Properties of Base Soils
Article
Under embankment dams and dykes, horizontal groundwater seepage prevails. If the subsoil is layered, and if some coarse layers are not appropriate filters for finer layers, there can be contact erosion at the interface between fine and coarse soils. In order to study contact erosion threshold, some base-soil and coarse-soil combinations were submitted to a flow parallel to the interface between the coarse soil and the base soil. Critical velocities and critical hydraulic gradients were measured for various base soils. Using effective base-soil grain diameter, an empirical expression for critical velocity was proposed that is well adapted for silts or sand/clay mixtures as well as for sands. The mass of eroded soil was measured relative to the flow velocity for each base-soil/coarse-soil setup. The shear stress applied to the interface between base soil and coarse soil was derived from the hydraulic gradient. Using an empirical relationship between applied shear stress and measured eroded mass, erosion rate was estimated for each base-soil/coarse-soil setup.
 
Article
This paper describes a laboratory program to investigate the mechanical and physicochemical properties of bauxite residue (red mud) at a site in the United Kingdom. The red mud storage facility has been recently decommissioned and has been considered for future rehabilitation and construction activity. Based on a suite of laboratory tests conducted on the red mud, the material has compression behavior similar to clayey soils, but frictional behavior closer to sandy soils. The red mud appears to be “structured” and has features consistent with sensitive, cemented clay soils. Chemical testing suggests that the agent causing the aggregation of particles is hydroxysodalite and that the bonds are reasonably strong and stable during compressive loading. Exposure of the red mud to acidic conditions causes dissolution of the hydroxysodalite and a loss of particle cementation. Hydration of the hydroxysodalite unit cells is significant, but does not affect the mechanical performance of the material. The shape, size, and electrically charged properties of the hydroxysodalite, goethite, and hematite in the red mud appear to be causing mechanical behavior with features consistent with clay and sand, without the presence of either quartz or clay minerals.
 
Article
Scale effects of shallow foundation bearing capacity on granular materials were investigated to further evaluate the trend of decreasing bearing capacity factor, N-gamma, with increasing footing width, B, observed by other researchers. Model-scale square and circular footing tests ranging in width from 0.025 to 0.914 m were performed on two compacted sands at three relative densities. Results of the model-scale footing tests show that the bearing capacity factor, N-gamma, is dependent on the absolute width of the footing for both square and circular footings. Although this phenomenon is well known, the current study used a large range of footing sizes tested on well-graded sands to show that the previously reported modifications to the bearing capacity factor, N-gamma using grain-size and reference footing width do not sufficiently account for the scale effect seen in the test results from this study. It also shows that behavior of most model-scale footing tests cannot be directly correlated to the behavior of full-scale tests because of differences in mean stresses experienced beneath footings of varying sizes. The relationship of the initial testing conditions (i.e., void ratio) of the sand beds and mean stress experienced beneath the footing (correlated to footing size) to the critical state line controls footing behavior and, therefore, model-scale tests must be performed at a lower density than a corresponding prototype footing in order to correctly predict behavior. Small footings were shown to have low mean stresses but high N-gamma values, which indicates high operative friction angles and may be related to the curvature of the Mohr-Coulomb failure envelope.
 
Article
The development of matric suctions in soils contributes to their shear strength, resulting in an enhanced factor of safety against bearing-capacity failure. In this paper, matric suction profiles of desiccated mine tailings are predicted from a steady-state solution for evaporative conditions, and from an isothermal mathematical model that simulates liquid and vapor water flow through soils. The shear-strength envelope with respect to matric suction is established by testing reconstituted tailings samples in a modified triaxial cell, in which matric suction can be controlled. The contribution of matric suction to the shear strength is interpreted as an additional apparent cohesion for use in bearing-capacity calculations. Because of the nonlinearity of the shear-strength profile, a numerical method of analysis is adopted to predict the ultimate bearing capacity of the desiccated tailings. A subsequent decrease in bearing capacity following 2D water infiltration into a partially capped tailings deposit and accompanying suction loss is investigated.
 
Article
A comprehensive laboratory evaluation of blending 9.5 mm 3/8 in. minus curbside-collected crushed glass CG with dredged material DM was conducted to evaluate their potential for beneficial use as fill materials for urban applications. Tests were performed on 100% CG USCS classification SP and 100% DM OH specimens and 20/ 80, 40/ 60, 50/ 50, 60/ 40, and 80/20 CG–DM blends dry weight percent CG content reported first . The addition of 20% CG resulted in a 10–20 point 33–67% reduction in wopt while increasing the dry density by approximately 1–3 kN/m3 for standard and modified levels of compaction, respectively. Simultaneously, the compressibility of the DM was reduced by approximately 50% and the hydraulic conductivity was reduced by 1 2 order of magnitude. The addition of 20% CG significantly decreased the moisture content and significantly improved the workability of the 100% DM, where workability refers to the ease of handling, transport, placement, and compaction of the CG–DM blends compared to 100% DM . CIŪ triaxial strength testing indicated effective friction angles of 34 and 37° for 100% DM and CG compacted to a minimum of 95% relative compaction by ASTM D1557, respectively. A peak effective friction angle of 39° occurred for the 60/40 and 80/20 CG–DM blends which were also 1 and 3 orders of magnitude more permeable than 100% DM, respectively. Related increases in cv resulted in decreased times required for consolidation. The range of properties obtainable by the CG–DM blends offers a versatility that allows for the design of fills that can be potentially optimized to meet multiple design parameters e.g. strength, settlement, drainage, or higher CG or DM content .
 
Article
Based on the laboratory results reported in a companion paper, three crushed glass–dredged material CG–DM blends were prepared and evaluated in the field to explore the feasibility of using CG–DM blends in general, embankment and structural fill applications. A trailer-mounted pugmill successfully prepared 20/ 80, 50/ 50, and 80/20 CG–DM blends dry weight percent CG content reported first within a tolerance of ±5 dry % by weight of the targeted percentages. Blending criteria were routinely met at pugmill throughputs up to 1,500 m3 / day. The constructed 20/80 CG–DM embankment was compacted to a minimum of 90% modified Proctor compaction, whereas the 50/50 and 80/20 CG–DM embankments were constructed to a minimum of 95% modified Proctor compaction. Twenty to 80% CG addition to DM resulted in 1.5–5.5 kN/m3 increases in field dry densities above 100% DM, densities not achievable with other DM stabilization techniques such as Portland cement, fly ash, and/or lime PC/FA/lime addition. CG substantially improved the workability of DM allowing construction with conventional equipment and three person crew while achieving very consistent and reproducible results during a timeline of frequent and heavy precipitation events. The 20/ 80, 50/ 50, and 80/20 CG–DM embankments were characterized by average cone tip resistances on the order of 1.0, 1.5, and 2.0 MPa, respectively. An environmental evaluation of 100% CG, DM and 50/50 CG–DM blend samples coupled with an economic analysis of a scaled-up commercial application illustrated that the CG–DM blending approach is potentially more cost effective than PC/FA/lime stabilization approaches. These features of CG–DM blending make the process attractive for use in urban and industrial settings.
 
Article
The results are presented of drained triaxial tests on a weakly bonded artificial soil in which the stress path direction has been changed partway through the shearing process. The effects of the previous shearing path history on the yield and failure surfaces are examined. Yield of the bonds occurs under each stress path direction followed, even when yield has previously occurred along another path. This demonstrates that bond breakdown is an anisotropic process. The position of yield was found to be independent of the previous shearing path history of the soil and occurred at points that corresponded to a yield surface defined for the current shearing path direction. However, the previous shearing path history of the soil did significantly affect the failure envelope. It is suggested that the bond yield surface is kinematic, in the sense that it is an expandable/shrinkable surface, but that it is not a moveable surface. It is postulated that the yield surface expands when volumetric strains are compressive and shrinks when the volumetric strains are dilatent.
 
Article
The writers introduce a design approach for braced excavations based directly on the data of carefully chosen soil tests, conceived within the framework of plasticity theory, but allowing for strain hardening. Mobilized shear stresses beneath and around braced excavations are found by a stability calculation based on a proposed plastic deformation mechanism. Strains required to mobilize these stresses are deduced from a direct simple shear test on a representative sample taken from a selected location in the plastic zone of influence. These strains are entered into a simple plastic deformation mechanism to predict boundary displacements. Hence, the proposed Mobilizable Strength Design (MSD) method can satisfy both safety and serviceability in a single step of calculation, without the need for finite element analyses. In this method, design parameters can be chosen rationally with regard to the initial state of soil, the stiffness following the appropriate stress path, and the level of acceptable deformations under working conditions. Examples demonstrating the success of the MSD method are given for a variety wall and soil conditions. Comparisons are made both with previously published field studies and with comprehensive nonlinear finite element analyses.
 
Article
Earth pressure cells, filtmeters, strain gauges, inclinometer casings, and survey reflectors were installed during construction of a reinforced concrete cantilever retaining wall. A data acquisition system with remote access monitored some 60 sensors on a continual basis. Analyses of the data indicated development of the active condition after translation of about 0.1% of the backfill height. The wall rotated into the backfill as a rigid body, but the top of the stem deflected away from the backfill, approximately equal in magnitude and opposite in. direction to the displacement from rigid body rotation. Loading on the wall back-calculated from strain gauge readings was consistent with active earth pressure. The maximum lateral force, about the same as the design value, occurred during compaction of the backfill. Observations that differed from standard assumptions included the passive earth pressure in front of the shear key being less than 10% of the design value and vertical stress below the heel being greater than the toe. Compaction-induced lateral stresses on the stem were sometimes twice the vertical stress.
 
Article
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 1999. Includes bibliographical references (p. 263). by Albert C. To. S.M.
 
Article
Correct evaluation of shear modulus and damping characteristics in soils under dynamic loading is key to both the fundamental understanding of soil behavior and the practical application of soil modeling programs. Dynamic centrifuge tests can contribute significant information about soil behavior, but great care must be taken over the signal processing techniques involved, and the test conditions are different from the laboratory experiments that form the database of existing knowledge. This paper outlines several factors that require careful consideration when deriving stiffness and damping parameters from centrifuge data. Shear modulus and damping degradation curves for a dry sand, saturated sand, soft clay and a model waste are then evaluated to explore some of the factors that are introduced during centrifuge tests. Stiffness is seen to be a more reliable parameter than damping ratio. Damping during centrifuge tests for certain materials appeared to differ from the expected values.
 
Article
Unstable flow can result in the formation of fingers during infiltration into dry soil. Centrifuge modeling is a potentially useful tool to study the relationship between finger size, spacing, and velocity. It can also be used to investigate solute transport in such fingers. Physical properties of the fingers are obtained for three tests conducted at elevated acceleration levels. A fourth test was conducted at 1g. The physical parameters compare well with theoretical predictions. To assess solute transport in fingers, a known concentration of solute was introduced after the fingers had formed. The resulting breakthrough curves were analyzed using the two-region model as well as the advection dispersion equation with appropriate initial and boundary conditions. Although the two-region model is physically more plausible, it was found to match the extensive tailing observed in the breakthrough curves only marginally better than the advection-dispersion equation.
 
Article
Tests were conducted to determine the variation of water content and pore water suction for compacted clayey soils. The soils had varying amounts of clay fraction with plasticities ranging from low to high plasticity. The unsaturated soil behavior was investigated for six conditions, covering a range of compactive efforts and water contents. The experimental data were fit to four commonly used models for the water content-pore water suction relationship. Each model provided a satisfactory fit to the experimental data. However, the individual parameters obtained from the curve fits varied significantly between models. The soil water characteristic curves (SWCCs) were more sensitive to changes in compaction effort than changes in compaction water content. At similar water contents, the pore water suction increased with increasing compaction effort for each compaction condition and soil type. For all compaction conditions, the lowest plasticity soils retained the smallest water content and the highest plasticity soils retained the highest water content at a specified suction. In addition, SWCCs for soils compacted in the laboratory and in the field were similar.
 
Article
This paper describes pioneering research to integrate a novel “electronic nose” (EN) technology with a membrane interface probe (MIP) for rapidly screening hydrocarbon contaminated sites. The electronic nose is an automated odor recognition device that detects and identifies chemical vapors based on the principles of human olfaction. The MIP is an in situ tool that samples volatile organic compounds from the subsurface and transports the vapor through tubing to analytical devices located on the surface. The electronic nose developed for this research was first trained and tested to identify vapor samples of benzene, toluene, ethyl benzene, and xylene at three different concentration levels. The integrated EN–MIP system was then tested in gasoline-spiked aqueous soil samples in the laboratory. In situ demonstration tests were conducted in collaboration with the U.S. EPA at a gasoline-contaminated site in Rhode Island. The EN–MIP system was successful in detecting and estimating the concentration levels of gasoline contamination at various depths.
 
Article
Lunar soil consists of dry silty sand. Observations and measurements conducted during Surveyor, Apollo, and Luna missions indicated that the lunar soil is unusually cohesive. This is attributable to the fact that thick layers of adsorbed gases, which coat and lubricate soil particles on Earth, are absent in the ultrahigh vacuum on the Moon. “Surface cleanliness” is introduced as a new parameter for describing soils in different planetary environments. It is defined as the dimensionless inverse of adsorbate thickness on solid surfaces. By this definition, the ultrahigh vacuum on the Moon is associated with high surface cleanliness, while Earth's atmosphere is associated with low surface cleanliness. A model is developed to calculate surface cleanliness and its effect on shear strength in any planetary environment. Results obtained from the model compare well with data from previous ultrahigh vacuum and variable temperature laboratory experiments on Earth soils. It is shown that surface cleanliness is an important parameter with respect to lunar soil shear strength.
 
Article
Sinkholes are surface depressions or shafts resulting from the collapse of a submerged cavity in soil. The cavities that lead to sinkholes form as a result of underlying geology in limestone areas, or as a result of human activity such as mining or leakage from a sewer. The formation of sinkholes is often sudden and can lead to extensive damage and loss of life, especially in urban areas. Much of the literature on the subject of sinkhole formation is empirical in nature, often being associated with specific locations. This paper presents the results of a study, using numerical modeling, of the undrained stability of the submerged cavities that lead to sinkhole formation. Finite-element limit analysis techniques (using programs developed at the University of Newcastle) are used to obtain upper and lower bound values of a suitable load parameter, which bracket the exact solution. The results are compared to analytical solutions, both from literature and derived independently.
 
Article
This paper reports results of a full-scale field test to assess the performance of dilute colloidal silica stabilizer in reducing the settlement of liquefiable soil. Slow injection methods were used to treat a 2-m-thick layer of liquefiable sand. Eight injection wells were installed around the perimeter of the 9-m-diameter test area and 8% by weight colloidal silica grout was slowly injected into the upper 2 m of a 10-m-thick layer of liquefiable sand. A central extraction well was used during grout injection to direct the flow of the colloidal silica towards the center of the test area. Details of the field injection are described. Subsequently, the injection wells were used to install explosive charges and liquefaction was induced by blasting. After blasting, approximately 0.3 m of settlement occurred versus 0.5 m of settlement in a nearby untreated area. The mechanism of improvement is thought to be bonding between the colloidal silica and the individual sand particles; the colloidal silica gel encapsulates the soil structure and maintains it during dynamic loading.
 
Article
Geosynthetic-reinforced column-supported (GRCS) embankments have increasingly been used in the recent years for accelerated construction. Numerical analyses have been conducted to improve understanding and knowledge of this complicated embankment system. However, most studies so far have been focused on its short-term or long-term behavior by assuming an undrained or drained condition, which does not consider water flow in saturated soft soil (i.e., consolidation). As a result, very limited attention has been paid to a settlement-time relationship especially postconstruction settlement, which is critical to performance of pavements on embankments or connection between approach embankments and bridge abutments. To investigate the time-dependent behavior, coupled two-dimensional mechanical and hydraulic numerical modeling was conducted in this study to analyze a well-instrumented geotextile-reinforced deep mixed column-supported embankment in Hertsby, Finland. In the mechanical modeling, soils and DM columns were modeled as elastic-plastic materials and a geotextile layer was modeled using cable elements. In the hydraulic modeling, water flow was modeled to simulate generation and dissipation of excess pore water pressures during and after the construction of the embankment. The numerical results with or without modeling water flow were compared with the field data. In addition, parametric studies were conducted to further examine the effects of geosynthetic stiffness, column modulus, and average staged construction rate on the postconstruction settlement and the tension in the geosynthetic reinforcement.
 
Laboratory compaction data with variable ZAV curves
Article
Compaction characteristics of municipal solid waste (MSW) were determined in the laboratory and in the field as a function of moisture content, compactive effort, and seasonal effects. Laboratory tests were conducted on manufactured wastes using modified and 4X modified efforts. Field tests were conducted at a MSW landfill in Michigan on incoming wastes without modifications to size, shape, or composition, using typical operational compaction equipment and procedures. Field tests generally included higher efforts and resulted in higher unit weights at higher water contents than the laboratory tests. Moisture addition to wastes in the field was more effective in winter than in summer due to dry initial conditions and potential thawing and softening of wastes. The measured parameters in the laboratory were γdmax-mod=5.2 kN/m3, wopt-mod=65%, γdmax-4 x mod=6.0 kN/m3, and wopt-4 x mod=56%; in the field with effort were γdmax-low=5.7 kN/m3, wopt-low=70%; γdmax-high=8.2 kN/m3, and wopt-high=73%; and in the field with season were γdmax-cold=8.2 kN/m3, wcold=79.5%, γdmax-warm=6.1 kN/m3, and wwarm=70.5%. Soil compaction theory was reasonably applicable to wastes with the exception that the Gs of waste solids increased with compactive effort resulting in steep degree of saturation curves and low change in wopt between efforts. Moisture addition to wastes during compaction increased the workability, the unit weight, and the amount of incoming wastes disposed, and reduced the compaction time. The combined effects have significant environmental and economic implications for landfill operations.
 
a Ratio of horizontal to vertical permeability along radial distance from drain in large scale consolidometer original data from Indraratna and Redana 1998b; b proposed horizontal permeability distribution for isotropic soil original data from Onoue et al. 1991
Axisymmetric unit cell 
Permeability distribution 
Predicted and measured settlements for large scale consolidometer
Article
A vertical drain radial consolidation equation based on a parabolic reduction in permeability toward the drain is presented. The proposed equation, based on Hansbo’s equal strain theory, is compared with settlement data from a laboratory test in a large scale consolidometer.
 
Base soils and filters with various uniformity coefficients C u but having the same retention ratio D 15 / d 85
A typical filter PSD and CSD showing passing probability p=1 − P c
Article
The filter design criteria in practice are currently based on laboratory tests that were carried out on uniform base soil and filter materials. These criteria mostly involve specific particle size ratios, where the system of base soil and filter is represented by some characteristic particle sizes. Consequently, these criteria have limitations when applied to nonuniform materials. In filters, it is the constriction size rather than the particle size that affects filtration. In this paper, a mathematical procedure to determine the controlling constriction size is introduced, and subsequently, a constriction-based retention criterion for granular filters is presented. The model also incorporates the effect of nonuniformity of base soil in terms of its particle size distribution, considering the surface area of the particles. The proposed retention criterion is verified based on experimental data taken from past studies plus large-scale filtration tests carried out by the authors. The model successfully and distinctly demarcates the boundary between effective and ineffective filters in the case of cohensionless base soils.
 
Article
Cover temperature variations were determined at four municipal solid waste landfills located in different climatic regions in North America: Michigan, New Mexico, Alaska, and British Columbia. Cover temperatures varied seasonally similarly to air temperatures and demonstrated amplitude decrement and phase lag with depth. Elevated temperatures in the underlying wastes resulted in warmer temperatures and low frost penetration in the covers compared to surrounding subgrade soils. The ranges of measured temperatures decreased and average temperatures generally increased (approximately 2°C/m) with depth. The ranges of measured temperatures (Tmax−Tmin) were 18–30°C and 13–21°C and the average temperatures were 13–18°C and 14–23°C at 1 and 2 m depths, respectively. For soil and geosynthetic barrier materials around 1 m depth, the maximum and minimum temperatures were 22–25°C and 3–4°C, respectively. Frost depths were determined to be approximately 50% of those for soils at ambient conditions. The main direction of heat flow in the covers was upward (negative gradients). The cover gradients varied between −18 and 14°C/m, with averages of −7 to 1°C/m. The gradients for soil and geosynthetic barrier materials around 1 m depth varied between −11 and 9°C/m with an average of −2°C/m. Cover thawing n-factors ranged between 1.0 and 1.4 and the cover freezing n-factor was 0.6. Design charts and guidelines are provided for cover thermal analyses for variable climatic conditions.
 
Article
To simplify a complicated problem, most previous investigations of wave-induced seabed response have been concerned with an isotropic seabed with uniform soil characteristics, even though strong evidence of anisotropic soil behavior and variable soil characteristics has been reported in soil mechanics literature. This paper proposes a finite-element model to investigate the response of a cross-anisotropic seabed with variable soil characteristics subjected to a three-dimensional short-crested wave system. Based on the present model, together with the liquefaction criterion, the wave-induced liquefaction potential can be estimated. The numerical results indicate that the influence of cross-anisotropic soil behavior and variable soil characteristics on the wave-induced seabed response (including liquefaction potential) cannot always be ignored without committing substantial errors.
 
Article
Several geotechnical engineering constructions subject the soil to a partial stress reduction. In addition, in practice, often both axi-symmetric and non axi-symmetric conditions can apply in different locations in the ground affected by the construction. In general, the corresponding stress states at failure will be, therefore, overconsolidated and cover a wide domain of the space of the principal stresses. However, the classic failure criteria typically fail to reproduce the observed failure envelope in wide range of stresses. In the Note, the original and Modified Lade's criteria are validated and compared against recent data on Pisa clay at general overconsolidated stress states, in compression and extension. A generalization of the Modified Lade's criterion at overconsolidated clays is also proposed. 2010 ASCE
 
Article
The seismic demand on potentially liquefiable soils can be approximated by a series of uniform shear stress cycles. Procedures are reviewed for converting an arbitrary acceleration time history to a series of uniform cycles with amplitude = 0.65 of the peak. The number of cycles (N) at this amplitude is evaluated so as to represent a seismic demand for liquefaction triggering equivalent to that of the accelerogram. An assumed relationship between N and magnitude (m) underlies so-called magnitude scaling factors used to adjust the liquefaction resistance of soil for the effects of duration/magnitude. Scaling factors can alternatively be related directly to N, which enables the effects of factors other than m (for example, site-source distance r) to be quantified. We develop empirical models for N that are applicable to active tectonic regions and find a strong dependence on m and r and a weaker dependence on site condition and near-fault rupture directivity effects. The model for N is used to develop new scaling factors for soil liquefaction resistance that are distance-dependent and have a defined level of uncertainty.
 
Article
This paper describes the results from an experimental program that has been conducted to investigate the distribution of earth pressure on a cylindrical wall embedded in granular material and subjected to radial displacement. The model shaft has been designed and built using mechanically adjustable segments to control the magnitude and uniformity of the wall movement during the tests. A series of experiments have been performed, and the progressive changes in earth pressure along the shaft have been continuously measured for different wall displacements. Results indicated a rapid decrease in lateral earth pressure when a small wall movement was introduced. When the wall movement reached about 2.5% of the shaft radius, the earth pressure distribution along the shaft became uniform and independent of any additional wall displacement. The experimental results are also compared with some of the available theoretical solutions, and the applicability of these solutions is then examined.
 
Article
Site investigation data used for the establishment of the reported relationships were provided by railway authorities in India and the relationships were subsequently used throughout a 65km section of railway line in the Eastern Ghats. During the early stages of construction of a railway line in southeast India, the tunneling works encountered numerous problems, such as rock falls, major water inflow, etc. In order to progress the works, it was necessary to undertake thorough classification of the rock masses and to obtain values of the in situ modulus of deformation for inputting into numerical analyses. It was not feasible to conduct a large number of in situ determinations of the modulus of deformation. Hence, an attempt was made to establish an empirical relationship between rock structure rating and modulus of deformation (Em) for the rock masses through which the railway passed. This was done using data from tests conducted on rock samples taken from 45 boreholes at various locations along the railway line, particularly in tunnel sections where distress was observed. (ASCE)
 
Article
No This paper presents results of the relationship between the degree of saturation and the matric suction head at static equilibrium and during dynamic flow of water using a Buchner funnel and a fully instrumented two-dimensional tank, respectively. The major influences of the dynamic flow on the relationships between the suction head and the degree of saturation are highlighted and discussed. The experimental results show that dynamic flow of water strongly affects the volume of entrapped air. The results also reveal that any scanning curve can be described as two parts, namely, transition and coinciding. The transition curve starts from the recent reversal degree of saturation and continues up to the previous reversal degree of saturation. The shape of the transition curve and the amount of hysteresis are not only a function of the reversal degree of saturation but are also a function of the saturation path history. The experimental results are used to examine the validity of the proposed analytical model by Parker and Lenhard in 1987 for describing the relationships between the degree of saturation and the matric suction head. It was found that Parker and Lenhard’s model provides a good prediction of the relations provided that care should be taken for the value of the reversal degree of saturation at zero suction head.
 
Article
This paper is mainly concerned with a laboratory study to investigate the effect of smear due to vertical drain installation. The extent of the smear zone around a vertical drain was studied utilizing a large-scale consolidometer apparatus. The test results reveal that a significant reduction in the horizontal permeability takes place toward a central drain, whereas the vertical permeabilty remains relatively unchanged. The radius of the smear zone was estimated to be a factor of four to five times the radius of the central drain (mandrel), and the measured ratio of horizontal to vertical permeability approached unity at the drain-soil interface. The laboratory measured settlements are subsequently compared with the predictions based on the theory of Hansbo and the finite element method. It is of relevance to note that the inclusion of the correct variation of permeability ratios of the smear zone in the plane strain finite element analysis improves the accuracy of settlement predictions.
 
Article
Remediation schemes for the treatment of liquefiable ground, such as vertical drains, have evolved over the last 30 years largely as a result of consideration of uniform sand beds. However, many liquefiable sites also contain thin layers of silts and clays which will act as an obstacle to fluid dissipating from liquefying sands, such that the performance and requirements of a remediation scheme will be different. In particular, water films may be produced. This paper presents results from a series of dynamic centrifuge experiments on vertical drains in level liquefiable sand deposits. Centrifuge tests were conducted both with and without surface fine layers. The drains prevented sand boiling, and the thin surface fine layers did not significantly affect excess pore pressure response. A further centrifuge test on a thin layer of low-permeability fines separating two liquefiable sandy layers, showed evidence suggesting that material boiled from the lower sand to the upper sand in the absence of a drain through the fines. All of the experiments suggest that the presence of unblocked vertical drains prevent water film formation.
 
Article
The present study provides a methodology to include the smear effect of vertical drains in a two-dimensional (2D) plane-strain finite-element model, employing the modified Cam-clay theory. The analysis is conducted by converting the radius of the smear zone and its permeability (axisymmetric) into equivalent plane strain parameters. The introduction of smear effects improves the accuracy of the numerical model that is tested for a Malaysian soft clay, in this study.
 
Article
Geotechnical centrifuge testing is used to examine the preferential (fingered) flow of a nonaqueous phase liquid (NAPL) in a uniform dry sand. The results of nine experiments, containing a total of 87 observations of NAPL finger behavior, are analyzed. The observed finger tip velocities range from 0.01 to 0.3 cm/s, while the observed finger widths range from 0.3 to 3.6 cm. From the experimental data it is concluded that, asymptotically, the NAPL fingers are not fully saturated. For comparison, the behavior of water fingers is examined using the same experimental setup. In contrast to the NAPL fingers, and in agreement with other work reported in the literature, the water fingers are found to be fully saturated. In addition, it is confirmed that the water finger properties can be well predicted from known porous medium and fluid properties. A scaling analysis is presented that allows the NAPL finger properties to be inferred from models developed to describe water finger properties. The analysis predicts NAPL finger velocities to within 15% and NAPL finger, widths to within 50% if both finger types are assumed saturated. By adjusting the analysis to account for the fact that the NAPL fingers are not fully saturated, NAPL finger widths can be predicted within to 10%, and NAPL finger velocities to within 30%.
 
Article
Dov Leshchinsky Traditionally, resultant force of lateral earth pressure serves as the basis for design nearly vertical walls. Conversely, slopes are designed to be stable using a factor of safety approach. However, with the availability of heavy facing elements such as gabions or with soil reinforcement combined with some facing system, steep slopes are increasingly being constructed. Steep slopes are considered to be unstable unless supported; that is, such slopes require facings to resist lateral earth pressure. Extending Coulomb‟s formulation to such slopes may not be conservative as a planar slip surface may not be critical. Presented are the results of a formulation to find the resultant lateral force which utilizes the log-spiral failure mechanism. The friction at the interface soil-facing is assumed to act on vertical surface only thus replicating the geometry of stacked rectangular facing units. Given the batter, the backslope, the height, the unit weight and design friction angle of the backfill, and the interface friction, one can quickly determine the corresponding lateral earth pressure coefficient. Formulation equivalent to Coulomb‟s is also presented. Its results show that for batters up to 20°, the common approach of using Coulomb method, including the assumed direction to coincide with the batter, yield results that are quite close to those stemming from the log-spiral analysis. Hence, use of Coulomb‟s analysis for such small batters is a reasonable as its formulation is simple. University of Delaware, Department of Civil and Environmental Engineering M.C.E.
 
Article
There is currently a lack of established calculation method for the geotechnical design of heat exchanger piles, although the technology is experiencing a fast expansion. Instead of quantifying the effects of temperature changes on the static behavior of heat exchanger piles, the common geotechnical practice is to apply a large overall security factor. This is done in order to be on the side of safety with respect to thermal effects. The few existing in situ experiments show that applying a thermal load induces a significant change in the stress-strain state of a pile. This paper presents a geotechnical numerical analysis method, based on the load transfer approach, which assesses the main effects of temperature changes on pile behavior. The method is validated on the basis of two in situ measurements of the loads and deformations experienced by heat exchanger test piles. The occurrence of critical design situations is further discussed. Some conclusions are formulated on concrete failure and the full mobilization of the pile shaft friction and base resistance during the operation of the heat exchange system.
 
Comparison of Calculated CSD with Measured CSD of Soria et al. (1993)
Article
This paper describes an analytical model of filtration for granular media, based on the mechanics of particle migration under hydraulic loads. A new equation to predict the probability of particle movement through a 3D network model of the filter voids has been developed. Void constriction sizes are determined based on the particle-size distribution and relative density of the filter. An important new development is the differentiation between particles that form part of the filter structure and fine particles that are loose within the filter voids, or coarse particles that are enmeshed in a matrix of fines. The rate of particle erosion and transport is governed by the consideration of mass and momentum conservation. The model describes the time-dependent change of flow rate and base and filter particle-size distribution, porosity, and permeability. The model has application in the design of granular filters for noncohesive uniform, well-, and broadly graded base and filter materials.
 
Article
The objective of this paper is to propose an explicit solution for the critical hydraulic gradient required to move a base particle within a pore channel. The particle is assumed to displace when the applied hydrodynamic forces exceed this critical hydraulic gradient. The current analysis is an extension of a previous study (Indraratna and Vafai 1997), where the limit equilibrium analysis was modified to include the effect of drag in the hydrodynamic force component. The theoretical model was examined in the laboratory using fine gravel filters and a cohesionless base soil consisting of very fine river sand.
 
Article
Building rehabilitation is critical for numerous older urban areas, many of which have inadequate foundations to support new demands. Consequently, development of practical methods to strengthen existing foundations is crucial. In engineering practice, both subsurface grouting and helical piers have been widely used to address these issues by strengthening the foundation. If the solid shaft of a typical helical pier is replaced by a hollow shaft, then helical piers provide the ability to deliver grout. It is hypothesized that these grouted helical pier systems could address foundation strengthening needs. This paper presents findings from an exploratory research program where grouting and pier placement tools were developed and tested on the large geotechnical centrifuge at the University of California, Davis. Experimental methods and procedures developed are presented, and observations regarding the formation of grout bulbs under different conditions are analyzed. Physical observation of the test specimens indicates that average grout bulb diameters of 0.6–1.9 times the helix diameter (Dh) are attainable. For similar grout mixes, 20–50% larger grout bulbs can be attained by adding just a modest amount of injection pressure. Future research may use these results to develop load performance data.
 
Top-cited authors
Craig H Benson
  • University of Virginia
Rodrigo Salgado
  • Purdue University
J. Carlos Santamarina
  • King Abdullah University of Science and Technology
B. Indraratna
  • University of Technology Sydney
I. M. Idriss
  • University of California, Davis