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Showing papers in "Journal of Geotechnical and Geoenvironmental Engineering in 2010"


Journal ArticleDOI
TL;DR: In this article, the feasibility of biogrouting as a ground improvement method is investigated using techniques and equipment similar to those used in potential applications, and the results of a large-scale experiment (100 m3 ) are presented.
Abstract: Biogrouting is a biological ground improvement method, in which microorganisms are used to induce carbonate precipitation in the subsurface in order to increase the strength and stiffness of granular soils. In this paper the results of a large-scale experiment ( 100 m3 ) are presented, in which the feasibility of biogrouting as a ground improvement method is investigated using techniques and equipment similar to those used in potential applications. In situ geophysical measurements were used to monitor the biogrouting process during treatment and indicated that the stiffness had increased significantly after one day of treatment. The results of unconfined compressive strength tests on samples which were excavated after treatment were used to assess the distribution of mechanical properties throughout the cemented sand body, which correlated quite well with the results of the in situ geophysical measurements. The stiffness increase could be quantified as a function of the injected volume of grouting agent...

620 citations


Journal ArticleDOI
Sung Eun Cho1
TL;DR: In this paper, a probabilistic slope stability analysis is presented, where two-dimensional random fields are generated based on a Karhunen-Loeve expansion in a fashion consistent with a specified marginal distribution function and an autocorrelation function, and a Monte Carlo simulation is used to determine the statistical response based on the generated random fields.
Abstract: In this paper, a numerical procedure for probabilistic slope stability analysis is presented. This procedure extends the traditional limit equilibrium method of slices to a probabilistic approach that accounts for the uncertainties and spatial variation of the soil strength parameters. In this study, two-dimensional random fields were generated based on a Karhunen-Loeve expansion in a fashion consistent with a specified marginal distribution function and an autocorrelation function. A Monte Carlo simulation was then used to determine the statistical response based on the generated random fields. This approach makes no assumption about the critical failure surface. Rather, the critical failure surface corresponding to the input random fields of soil properties is searched during the process of analysis. A series of analyses was performed to verify the application potential of the proposed method and to study the effects of uncertainty due to the spatial heterogeneity on the stability of slope. The results show that the proposed method can efficiently consider the various failure mechanisms caused by the spatial variability of soil property in the probabilistic slope stability assessment.

273 citations


Journal ArticleDOI
TL;DR: In this article, the authors investigated the qualitative and quantitative improvement of individual load capacity of stone column by encasement through laboratory model tests conducted on stone columns installed in clay bed prepared in controlled condition in a large scale testing tank.
Abstract: The stone columns (or granular piles) are increasingly being used as ground reinforcement elements for supporting a wide variety of structures including buildings and flexible structures. The stone columns derive their load capacity from the confinement offered by the surrounding soil. In very soft soils this lateral confinement may not be adequate and the formation of the stone column itself may be doubtful. Wrapping the individual stone columns with suitable geosynthetic is one of the ideal forms of improving the performance of stone columns. This type of encasement by geosynthetic makes the stone columns stiffer and stronger. In addition, encasement prevents the lateral squeezing of stones in to the surrounding clay soil and vice versa, preserves drainage function of the stone column and frictional properties of the aggregates. In spite of many advantages, the behavior and the mechanism of the geosynthetic encased stone columns is not thoroughly understood. This paper investigates the qualitative and quantitative improvement of individual load capacity of stone column by encasement through laboratory model tests conducted on stone columns installed in clay bed prepared in controlled condition in a large scale testing tank. The load tests were performed on single as well as group of stone columns with and without encasement. Tests were performed with different geosynthetics for the encasement of stone column. The results from the load tests indicated a clear improvement in the load capacity of the stone column due to encasement. The increase in the axial load capacity depends very much upon the modulus of the encasement and the diameter of the stone column. The increase in the stress concentration on the stone columns due to encasement was also measured in the tests. The results from the tests were used to develop the design guidelines for the design of geosynthetic encasement for the given load and settlement.

246 citations


Journal ArticleDOI
TL;DR: In this article, the authors proposed a multiblock failure mechanism for a circular tunnel driven by a pressurized shield, which is based on a translational three-dimensional multi-block failure mechanism.
Abstract: The aim of this paper is to determine the face collapse pressure of a circular tunnel driven by a pressurized shield. The analysis is performed in the framework of the kinematical approach of limit analysis theory. It is based on a translational three-dimensional multiblock failure mechanism. The present failure mechanism has a significant advantage with respect to the existing limit analysis mechanisms developed in the case of a frictional soil: it takes into account the entire circular tunnel face and not only an inscribed ellipse to this circular area. This was made possible by the use of a spatial discretization technique. Hence, the three-dimensional failure surface was generated "point by point" instead of simple use of existing standard geometric shapes such as cones or cylinders. The numerical results have shown that a multiblock mechanism composed of three blocks is a good compromise between computation time and results accuracy. The present method significantly improves the best available solutions of the collapse pressure given by other kinematical approaches. Design charts are given in the case of a frictional and cohesive soil for practical use in geotechnical engineering.

237 citations


Journal ArticleDOI
TL;DR: In this paper, a field trial was conducted on an instrumented track at Bulli, New South Wales, Australia with the specific aims of studying the benefits of a geocomposite installed at the ballast-capping interface, and to evaluate the performance of moderately graded recycled ballast in comparison to traditionally very uniform fresh ballast.
Abstract: Understanding the complex mechanisms of stress transfer and strain accumulation in layers of track substructure under repeated wheel loading is essential to predict the desirable track maintenance cycle as well as the design of the new track. Various finite element and analytical techniques have been developed in the past to understand the behavior of composite track layers subjected to repeated wheel loads. The mechanical behavior of ballast is influenced by several factors, including the track confining pressure, type of aggregates, and the number of loading cycles. A field trial was conducted on an instrumented track at Bulli, New South Wales, Australia, with the specific aims of studying the benefits of a geocomposite installed at the ballast-capping interface, and to evaluate the performance of moderately graded recycled ballast in comparison to traditionally very uniform fresh ballast. It was found that recycled ballast can be effectively reused if reinforced with a geocomposite. It was also found t...

224 citations


Journal ArticleDOI
TL;DR: In this article, a series of centrifuge experiments involving buildings situated atop a layered soil deposit have been performed to identify the mechanisms involved in liquefaction-induced building settlement, including building-induced shear deformations combined with localized volumetric strains during partially drained cyclic loading are the dominant mechanisms.
Abstract: Seismically induced settlement of buildings with shallow foundations on liquefiable soils has resulted in significant damage in recent earthquakes. Engineers still largely estimate seismic building settlement using procedures developed to calculate postliquefaction reconsolidation settlement in the free-field. A series of centrifuge experiments involving buildings situated atop a layered soil deposit have been performed to identify the mechanisms involved in liquefaction-induced building settlement. Previous studies of this problem have identified important factors including shaking intensity, the liquefiable soil's relative density and thickness, and the building's weight and width. Centrifuge test results indicate that building settlement is not proportional to the thickness of the liquefiable layer and that most of this settlement occurs during earthquake strong shaking. Building-induced shear deformations combined with localized volumetric strains during partially drained cyclic loading are the dominant mechanisms. The development of high excess pore pressures, localized drainage in response to the high transient hydraulic gradients, and earthquake-induced ratcheting of the buildings into the softened soil are important effects that should be captured in design procedures that estimate liquefaction-induced building settlement.

210 citations


Journal ArticleDOI
TL;DR: In this article, an extensive database of 300 case histories of wall displacements and ground settlements due to deep excavations in Shanghai soft soils were collected and analyzed, and the mean values of the maximum lateral displacements of wall constructed by the top-down method, walls constructed by bottom-up method, including diaphragm walls, contiguous pile walls, and compound deep soil mixing walls were analyzed.
Abstract: An extensive database of 300 case histories of wall displacements and ground settlements due to deep excavations in Shanghai soft soils were collected and analyzed. The mean values of the maximum lateral displacements of walls constructed by the top-down method, walls constructed by the bottom-up method (including diaphragm walls, contiguous pile walls, and compound deep soil mixing walls), sheet pile walls, compound soil nail walls, and deep soil mixing walls are 0.27%H, 0.4%H, 1.5%H, 0.55%H, and 0.91%H, respectively, where H is the excavation depth. The mean value of the maximum ground surface settlement is 0.42%H. The settlement influence zone reaches to a distance of about 1.5H to 3.5H from the excavation. The ratio between the maximum ground surface settlement and the maximum lateral displacement of a wall generally ranges from 0.4 to 2.0, with an average value of 0.9. The factors affecting the deformation of the wall were analyzed. It shows that there is a slight evidence of a trend for decreasing wall displacement with increasing system stiffness and the factor of safety against basal heave. Wall and ground movements were also compared with that observed in worldwide case histories.

196 citations


Journal ArticleDOI
TL;DR: In this article, the authors deal with the modeling of failure and post-failure stage of shallow landslides of the flow-type that often affect natural shallow deposits of colluvial, weathered, and pyroclastic origin.
Abstract: The paper deals with the modeling of failure and postfailure stage of shallow landslides of the flow-type that often affect natural shallow deposits of colluvial, weathered, and pyroclastic origin. The failure stage is frequently associated to rainfall that directly infiltrates the slope surface and to spring from the underlying bedrock. The postfailure stage is characterized by the sudden acceleration of the failed mass. The geomechanical modeling of both stages, based on site conditions and soil mechanical behavior, represents a fundamental issue to properly assess the failure conditions and recognize the potential for long travel distances of the failed soil masses. To this aim, in this paper, the current literature on the failure and postfailure stages of the shallow landslides of the flow-type is first reviewed. Then, an approach for their geomechanical modeling is proposed and three different modeling alternatives are presented. These models are then used to analyze, at different scales, a relevant case study of Southern Italy Sarno-Quindici event, May 4-5, 1998. Numerical analyses outline that both site conditions and hydraulic boundary conditions are among the key factors to evaluate the reliability of landslides of the flow-type. The potentialities and limitations of the available models are also evidenced as well as the perspectives related to the use of more advanced numerical models.

189 citations


Journal ArticleDOI
TL;DR: In this article, the influence of the selection of input ground motions on equivalent-linear site response analysis is evaluated through analyses performed with multiple suites of input motions selected to fit the same target acceleration response spectrum.
Abstract: Seismic site response analysis evaluates the influence of local soil conditions on earthquake ground shaking. There are multiple sources of potential uncertainty in this analysis; the most significant pertaining to the specification of the input motions and to the characterization of the soil properties. The influence of the selection of input ground motions on equivalent-linear site response analysis is evaluated through analyses performed with multiple suites of input motions selected to fit the same target acceleration response spectrum. The results indicate that a stable median surface response spectrum (i.e., within ±20% of any other suite) can be obtained with as few as five motions, if the motions fit the input target spectrum well. The stability of the median is improved to ±5 to 10% when 10 or 20 input motions are used. If the standard deviation of the surface response spectra is required, at least 10 motions (and preferably 20) are required to adequately model the standard deviation. The influence of soil characterization uncertainty is assessed through Monte Carlo simulations, where variations in the shear-wave velocity profile and nonlinear soil properties are considered. Modeling shear-wave velocity variability generally reduces the predicted median surface motions and amplification factors, most significantly at periods less than the site period. Modeling the variability in nonlinear properties has a similar, although slightly smaller, effect. Finally, including the variability in soil properties significantly increases the standard deviation of the amplification factors but has a lesser effect on the standard deviation of the surface motions.

170 citations


Journal ArticleDOI
TL;DR: In this article, a program of splitting tensile tests and unconfined compression tests considering three distinct voids ratio and seven cement contents, varying from 1 to 12%, was carried out in the present study.
Abstract: The enhancement of local soils with cement for the construction of stabilized pavement bases, canal lining, and support layer for shallow foundations shows great economical and environmental advantages, avoiding the use of borrow materials from elsewhere, as well as the need of a spoil area. The present research aims to quantify the influence of the amount of cement, the porosity, and the voids/cement ratio in the assessment of unconfined compressive strength qu and splitting tensile strength qt of an artificially cemented sand, as well as in the evaluation of qt /qu relationship. A program of splitting tensile tests and unconfined compression tests considering three distinct voids ratio and seven cement contents, varying from 1 to 12%, was carried out in the present study. The results show that a power function adapts well qt and qu values with increasing cement content and with reducing porosity of the compacted mixture. The voids/cement ratio is demonstrated to be an appropriate parameter to assess both qt and qu of the sand-cement mixture studied. Finally, the qt /qu relationship is unique for the sand-cement studied, being independent of the voids/cement ratio. DOI: 10.1061/ASCEGT.1943-5606.0000278 CE Database subject headings: Tensile strength; Compressive strength; Soil cement; Compacted soils. Author keywords: Tensile strength; Compressive strength; Soil cement; Compacted soils.

168 citations


Journal ArticleDOI
TL;DR: In this article, a modified recovery of equilibrium in patches technique was developed to map stresses after each remeshing, and the results showed that the anchor roughness had minimal effect on anchor performance.
Abstract: Three-dimensional large deformation finite-element (FE) analyses were performed to investigate plate anchor capacity during vertical pullout. The remeshing and interpolation technique with small strain approach was expanded from two-dimensional to three-dimensional conditions and coupled with the FE software, ABAQUS. A modified recovery of equilibrium in patches technique was developed to map stresses after each remeshing. Continuous pullout of rectangular plate anchors was simulated and the large deformation results for strip, circular, and rectangular anchors were compared with model test data, small strain FE results, and plastic limit solutions. Interface conditions of no breakaway (bonded) and immediate breakaway (no tension) were considered at the anchor base. The effects of anchor roughness, aspect ratio, soil properties, and soil overburden pressure were investigated. It was found that the anchor roughness had minimal effect on anchor performance. For square and circular deep anchors under immediate breakaway conditions, the maximum uplift capacity increased with soil elastic modulus, which suggests that lower bound limit analysis and small strain FE analysis may overestimate the capacity. The soil beneath the anchor base separates from the anchor at a certain embedment depth near the mudline, once tensile stresses were generated. The ratio of separation depth to anchor width was found to increase linearly with the ratio of soil undrained shear strength to the product of soil effective unit weight and anchor width and was independent of the initial anchor embedment depth.

Journal ArticleDOI
TL;DR: In this article, the authors developed a simple correlation between peak friction angle, critical-state friction angle and dilatancy based on triaxial compression and plane-strain compression test data for sand for a range of confining pressures.
Abstract: Sand dilates with shearing at a rate that increases with increasing relative density DR and decreases with increasing effective confining stress c. The peak friction angle of a sand depends on its critical-state friction angle and on dilatancy. In this paper, we develop a simple correlation between peak friction angle, critical-state friction angle, and dilatancy based on triaxial compression and plane-strain compression test data for sand for a range of confining pressures from very low levels to approximately 196 kPa. DOI: 10.1061/ASCEGT.1943-5606.0000237 CE Database subject headings: Sand, Soil type; Stress; Dilatancy; Shear strength; Friction. Author keywords: Sand; Low confining stress; Dilatancy; Shear strength; Friction angle.

Journal ArticleDOI
TL;DR: In this article, a series of unsaturated consolidated drained triaxial tests were conducted on statically compacted sand-kaolin specimens under drying and wetting to examine the validity of the proposed equations.
Abstract: Shear strength of unsaturated soil is an important engineering property in various geotechnical designs. In response to varying climatic conditions, unsaturated soil behaves differently under the drying and wetting processes due to hysteresis. Many research works were conducted and numerous equations were proposed for unsaturated shear strength, however, most of them were limited to the soil under the drying process. In this study, shear strength equations were categorized according to the nature of equation, i.e., fitting and prediction type equations. The purpose of this study is to propose prediction type shear strength equations for unsaturated soil under drying and wetting. Twelve published shear strength equations were selected for evaluation. A series of unsaturated consolidated drained triaxial tests were conducted on statically compacted sand-kaolin specimens under drying and wetting to examine the validity of the proposed equations. The experimental results indicated that the specimens on the drying path had a higher shear strength and exhibited more ductility, less stiffness, and contraction during shearing while the specimens on the wetting path had a lower shear strength and exhibited more brittleness, more stiffness, and dilation during shearing. The proposed equations were shown to provide the best predictions on the drying and wetting shear strength results from this study as well as published data in the comparison study.

Journal ArticleDOI
TL;DR: In this article, the authors evaluated the relative importance of key settlement mechanisms by using mitigation techniques to minimize some of their respective contributions and found that the importance of settlement mechanisms depend on the characteristics of the earthquake motion, liquefiable soil, and building.
Abstract: The effective application of liquefaction mitigation techniques requires an improved understanding of the development and consequences of liquefaction. Centrifuge experiments were performed to study the dominant mechanisms of seismically induced settle- ment of buildings with rigid mat foundations on thin deposits of liquefiable sand. The relative importance of key settlement mechanisms was evaluated by using mitigation techniques to minimize some of their respective contributions. The relative importance of settlement mechanisms was shown to depend on the characteristics of the earthquake motion, liquefiable soil, and building. The initiation, rate, and amount of liquefaction-induced building settlement depended greatly on the rate of ground shaking. Engineering design procedures should incorporate this important feature of earthquake shaking, which may be represented by the time rate of Arias intensity i.e., the shaking intensity rate. In these experiments, installation of an independent, in-ground, perimetrical, stiff structural wall minimized deviatoric soil deformations under the building and reduced total building settlements by approximately 50%. Use of a flexible impermeable barrier that inhibited horizontal water flow without preventing shear deformation also reduced permanent building settlements but less significantly.

Journal ArticleDOI
TL;DR: In this paper, an experimental and analytical program was designed and conducted to evaluate the magnitude and distribution of seismically induced lateral earth pressures on cantilever retaining structures with dry medium dense sand backfill.
Abstract: An experimental and analytical program was designed and conducted to evaluate the magnitude and distribution of seismically induced lateral earth pressures on cantilever retaining structures with dry medium dense sand backfill. Results from two sets of dynamic centrifuge experiments and two-dimensional nonlinear finite-element analyses show that maximum dynamic earth pressures monotonically increase with depth and can be reasonably approximated by a triangular distribution. Moreover, dynamic earth pressures and inertia forces do not act simultaneously on the cantilever retaining walls. As a result, designing cantilever retaining walls for maximum dynamic earth pressure increment and maximum wall inertia, as is the current practice, is overly conservative and does not reflect the true seismic response of the wall-backfill system. The relationship between the seismic earth pressure increment coefficient (ΔK AE ) at the time of maximum overall wall moment and peak ground acceleration obtained from our experiments suggests that seismic earth pressures on cantilever retaining walls can be neglected at accelerations below 0.4 g. This finding is consistent with the observed good seismic performance of conventionally designed cantilever retaining structures.

Journal ArticleDOI
TL;DR: In this article, the kinematic approach of limit analysis is explored in three-dimensional (3D) stability analysis of slopes, and a formal derivation is first shown indicating that, in a general case, the approach yields an upper bound to the critical height of the slope or upper bound on the safety factor.
Abstract: The kinematic approach of limit analysis is explored in three-dimensional (3D) stability analysis of slopes. A formal derivation is first shown indicating that, in a general case, the approach yields an upper bound to the critical height of the slope or an upper bound on the safety factor. A 3D failure mechanism is used to produce stability charts for slopes. The slope safety factor can be read from the charts without the need for iterations. While two-dimensional (2D) analyses of uniform slopes lead to lower safety factors than 3D analyses do, a 3D calculation is justified in cases where the width of the collapse mechanism has physical limitations, for instance, in the case of excavation slopes, or when the analysis is carried out to back-calculate the properties of the soil from 3D failure case histories. Also, a 3D failure can be triggered by a load on a portion of the surface area of the slope. Calculations indicate that for the 3D safety factor of the loaded slope to become lower than the 2D factor f...

Journal ArticleDOI
TL;DR: In this article, the effect of groundwater table position, rainfall intensities, and soil properties in affecting slope stability was investigated in three different groundwater table positions corresponding to the wettest, typical, and driest periods in Singapore and four different rainfall intensity (9, 22, 36, and 80 mm/h).
Abstract: Rainfall, hydrological condition, and geological formation of slope are important contributing factors to slope failures. Parametric studies were carried out to study the effect of groundwater table position, rainfall intensities, and soil properties in affecting slope stability. Three different groundwater table positions corresponding to the wettest, typical, and driest periods in Singapore and four different rainfall intensities (9, 22, 36, and 80 mm/h) were used in the numerical analyses. Typical soil properties of two main residual soils from the Bukit Timah Granite and the sedimentary Jurong Formation in Singapore were incorporated into the numerical analyses. The changes in factor of safety during rainfall were not affected significantly by the groundwater table near the ground surface due to the relatively small changes in matric suction during rainfall. A delay in response of the minimum factor of safety due to rainfall and a slower recovery rate after rainfall were observed in slopes from the sedimentary Jurong Formation as compared to those slopes from the Bukit Timah Granite. Numerical analyses of an actual residual soil slope from the Bukit Timah Granite at Marsiling Road and a residual soil slope from the sedimentary Jurong Formation at Jalan Kukoh show good agreement with the trends observed in the parametric studies.

Journal ArticleDOI
TL;DR: In this article, three-dimensional finite element analyses were performed to study the behavior of piles in sloping ground under undrained lateral loading conditions, and analytical formulations were derived for the ultimate load per unit length and the initial stiffness of hyperbolic p-y curves.
Abstract: Three-dimensional finite element analyses were performed to study the behavior of piles in sloping ground under undrained lateral loading conditions. Piles of different diameter and length in sloping cohesive soils of different undrained shear strength and several ground slopes were considered. Based on the results of the finite element analyses, analytical formulations are derived for the ultimate load per unit length and the initial stiffness of hyperbolic p-y curves. New p-y criteria for static loading of piles in clay are proposed, which take into account the inclination of the slope and the adhesion of the pile-slope interface. These curves are used through a commercial subgrade reaction computer code to parametrically analyze the effect of slope inclination and pile adhesion on lateral displacements and bending moments. To validate the proposed p-y curves, a number of well documented lateral load tests are analyzed. Remarkable agreement is obtained between predicted and measured responses for a wide range of soil undrained shear strength and pile diameter, length, and stiffness.

Journal ArticleDOI
TL;DR: In this article, a cyclic triaxial test was conducted for compacted silt specimens with varying dry density, water content, dynamic stress, and load frequency to study the dynamic stability of a silt subgrade subjected to train traffic loading with increasing speed.
Abstract: The comfort and safety of a moving train is largely determined by the dynamic response of the railway track and its foundation (i.e., subgrade). To study the dynamic stability of a silt subgrade subjected to train traffic loading with increasing speed, cyclic triaxial tests were conducted for compacted silt specimens with varying dry density, water content, dynamic stress, and load frequency. The laboratory test results and field measurements of the subgrade dynamic stress under train loading indicate that with increasing train speed, an increase in dynamic stress and load frequency does not impair the stability of the silt subgrade, provided the subgrade is in sound physical condition (i.e., its natural water content approximates the optimal water content) and the relative compaction is at least 90%. However, if the relative compaction is 85%, the subgrade is stable only at a dynamic stress level that is below 70 kPa, and the subgrade may suffer shear failure at a higher dynamic stress level. The elastic deformation of the subgrade linearly increases with an increase in train speed. However, if the degree of saturation of the silt subgrade increases, the thresholds of both the dynamic stress and resilient modulus decrease markedly, accompanied by sharp increases in elastic deformation and cumulative deformation and can even result in the shear failure of the subgrade. These conditions are unfavorable for the high speeds and stability needed for trains; therefore, train speeds should be limited in wet conditions to reduce subgrade dynamic stress and load frequency.

Journal ArticleDOI
TL;DR: In this paper, the authors present the results of a numerical investigation into the performance of geosynthetic-encased stone columns (GESCs) installed in soft ground for embankment construction.
Abstract: This paper presents the results of a numerical investigation into the performance of geosynthetic-encased stone columns (GESCs) installed in soft ground for embankment construction. A three-dimensional finite-element model was employed to carry out a parametric study on a number of governing factors such as the consistency of soft ground, the geosynthetic encasement length and stiffness, the embankment fill height, and the area replacement ratio. The results indicate among other things that additional confinement provided by the geosynthetic encasement increases the stiffness of the stone column and reduces the degree of embankment load transferred to the soft ground, thereby decreasing the overall settlement. It is also shown that the geosynthetic encasement has a greater impact for cases with larger stone column spacing and/or weaker soil. Also revealed is that unlike isolated column loading conditions, full encasement may be necessary to ensure maximum settlement reduction when implementing GESCs under an embankment loading condition. Practical implications of the findings are discussed in detail.

Journal ArticleDOI
TL;DR: In this article, cone penetration test-based relationships are used to evaluate the susceptibility to strength loss and liquefied shear strength for a wide range of soils, and extrapolation beyond the case-history data are guided by laboratory studies and theory.
Abstract: Flow liquefaction is a major design issue for large soil structures such as mine tailings impoundments and earth dams. If a soil is strain softening in undrained shear and, hence, susceptible to flow liquefaction, an estimate of the resulting liquefied shear strength is required for stability analyses. Many procedures have been published for estimating the residual or liquefied shear strength of cohesionless soils. This paper presents cone penetration test-based relationships to evaluate the susceptibility to strength loss and liquefied shear strength for a wide range of soils. Case-history analyses by a number of investigators are reviewed and used with some additional case histories. Extrapolations beyond the case-history data are guided by laboratory studies and theory.

Journal ArticleDOI
TL;DR: In this article, two methods for probabilistic back-analysis of slope failure are presented for a general slope stability model, which can be back-analyzed with an optimization procedure that can be implemented in a spreadsheet.
Abstract: Back-analysis of slope failure is often performed to improve one's knowledge on parameters of a slope stability analysis model. In a failed slope, the slip surface may pass through several layers of soil. Therefore, several sets of model parameters need to be back-analyzed. To back-analyze multiple sets of slope stability parameters simultaneously under uncertainty, the back-analysis can be implemented in a probabilistic way, in which uncertain parameters are modeled as random variables, and their distributions are improved based on the observed slope failure information. In this paper, two methods are presented for probabilistic back-analysis of slope failure. For a general slope stability model, its uncertain parameters can be back-analyzed with an optimization procedure that can be implemented in a spreadsheet. When the slope stability model is approximately linear, its parameters can be back-analyzed with sensitivity analysis instead. A feature of these two methods is that they are easy to apply. Two case studies are used to illustrate the proposed methods. The case studies show that the degrees of improvement achieved by the back-analysis are different for different parameters, and that the parameter contributing most to the uncertainty in factor of safety is updated most.

Journal ArticleDOI
TL;DR: In this paper, the consequences of treating sulfate laden soils with calcium-based stabilizers are discussed and the nature (chemistry and structure) of the minerals (ettringite/thaumasite) blamed for deleterious reactions and why these structures may lead to damage.
Abstract: Civil engineers are at times required to stabilize sulfate-bearing clay soils with calcium-based stabilizers Deleterious heaving in these stabilized soils may result over time This paper addresses critical questions regarding the consequences of treating sulfate laden soils with calcium-based stabilizers The authors describe the nature (chemistry and structure) of the minerals (ettringite/thaumasite) blamed for deleterious reactions and explain why these structures may lead to damage The writers also describe the mechanisms of the mineral growth, and the extent of mineral growth based on the amount of sulfate minerals present in the soil The writers explain why the rate of ettringite growth in treated soils should not be expected to follow a controlled rate of ettringite development such as that which normally occurs in portland cement concrete The writers compare the rate and degree of ettringite development in soils to the classical model of nucleation and growth typical of most crystal structures Finally, the writers evaluate the role of soil mineralogy in controlling soil behavior at varying sulfate contents and verify the existence of a threshold level of soluble sulfates in soils that can trigger substantial ettringite growth

Journal ArticleDOI
TL;DR: In this article, the authors focus on three cases in which pile-supported embankments were used for constructing highways in the eastern coastal region of China, and provide a description of the soil profile, construction procedure, and field monitoring of the settlements, earth pressures, and pore-water pressures.
Abstract: When designing embankments over soft soils, geotechnical engineers face many challenges. These include potential bearing failure, intolerable settlement, and global or local instability. Pile-supported embankments have been emerged as an effective alternative successfully adopted worldwide to solve these problems. This paper focuses on three cases in which pile-supported embankments were used for constructing highways in the eastern coastal region of China. Each case provides a description of the soil profile, construction procedure, and field monitoring of the settlements, earth pressures, and pore-water pressures. Field monitored data from contact pressures acting on the piles and the soils, to the settlements of the piles and the soils are reported and discussed. The development of the earth pressures both on the piles and the soils shows that there was a significant soil arching in the embankment, and the measured earth pressures acting on the piles are much higher than that acting on the soils betwee...

Journal ArticleDOI
TL;DR: In this paper, the problem of tunneling beneath buried pipelines and the relationship between soil strains and pipeline bending behavior was examined. But, the authors focused on the tunnel deformation rather than the pipe bending behavior.
Abstract: The paper examines the problem of tunneling beneath buried pipelines and the relationship between soil strains and pipeline bending behavior. Data are presented from centrifuge tests in which tunnel volume loss was induced in sand beneath pipelines of varying stiffness properties. The model tunnel and pipelines were all placed at a Perspex wall of the centrifuge strong box such that image-based deformation analyses could be performed. The method provided detailed data of subsurface soil and pipe displacements and illustrated the soil-pipe interaction mechanisms that occurred during tunnel volume loss, including the formation of a gap beneath the pipes. The relationship between tunnel volume loss, soil strain, and pipe bending behavior is illustrated. Experimental results of pipe bending moments are compared against predictions: (1) assuming the pipe simply follows greenfield displacements; (2) using an elastic continuum solution; and (3) using a new method in which an "out-of-plane" shear argument, due to soil-pipe interaction, is introduced into the elastic continuum solution. It is shown that the new method gives the best prediction of experimental pipe bending moments.

Journal ArticleDOI
TL;DR: In this article, the results of static lateral load tests carried out on 1×2, 2×2, 1×4, and 3×3 model pile groups embedded in soft clay are presented.
Abstract: This paper presents the results of static lateral load tests carried out on 1×2 , 2×2 , 1×4 , and 3×3 model pile groups embedded in soft clay. Tests were carried out on piles with length to diameter ratios of 15, 30, and 40 and three to nine pile diameter spacing. The effects of pile spacing, number of piles, embedment length, and configuration on pile-group interaction were investigated. Group efficiency, critical spacing, and p multipliers were evaluated from the experimental study. The experimental results have been compared with those obtained from the program GROUP. It has been found that the lateral capacity of piles in 3×3 group at three diameter spacing is about 40% less than that of the single pile. Group interaction causes 20% increase in the maximum bending moment in piles of the groups with three diameter spacing in comparison to the single pile. Results indicate substantial difference in p multipliers of the corresponding rows of the linear and square pile groups. The predicted field group be...

Journal ArticleDOI
TL;DR: In this paper, an extensive direct shear testing program was implemented using coarse and fine sands tested with three types of fibers and a comparison between measured and predicted shear strengths indicated that the energy dissipation model is effective in predicting the shear strength of fiber-reinforced specimens.
Abstract: Soil reinforcement using discrete randomly distributed fibers has been widely investigated over the last 30 years. Several models were suggested to estimate the improvement brought by fibers to the shear strength of soils. The objectives of this paper are to (1) supplement the data available in the literature on the behavior of fiber-reinforced sands; (2) study the effect of several parameters which are known to affect the shear strength of fiber-reinforced sands; and (3) investigate the effectiveness of current models in predicting the improvement in shear strength of fiber-reinforced sand. An extensive direct shear testing program was implemented using coarse and fine sands tested with three types of fibers. Results indicate the existence of a fiber-grain scale effect which is not catered for in current prediction models. A comparison between measured and predicted shear strengths indicates that the energy dissipation model is effective in predicting the shear strength of fiber-reinforced specimens in reference to the tests conducted in this study. On the other hand, the effectiveness of the predictions of the discrete model is affected by the parameters of the model, which may depend on the test setup and the procedure used for mixing the fibers.

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TL;DR: In this article, a lognormal random vector is used to model the curve-fitting parameters of the soil-water characteristic curve (SWCC) and the engineering impact of adopting a probabilistic SWCC is briefly discussed by studying the uncertainty of unsaturated shear strength due to the uncertainty in SWCC.
Abstract: Direct measurement of the soil-water characteristic curve (SWCC) is costly and time consuming. A first-order estimate from statistical generalization of experimental data belonging to soils with similar textural and structural properties is useful. A simple approach is to fit the data with a nonlinear function and to construct an appropriate probability model of the curve-fitting parameters. This approach is illustrated using sandy clay loam, loam, loamy sand, clay, and silty clay data in Unsaturated Soil Database. This paper demonstrates that a lognormal random vector is suitable to model the curve-fitting parameters of the SWCC. Other probability models using normal, gamma, Johnson, and other distributions do not provide better fit than the proposed lognormal model. The engineering impact of adopting a probabilistic SWCC is briefly discussed by studying the uncertainty of unsaturated shear strength due to the uncertainty of SWCC.

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TL;DR: In this paper, the pore-size distributions (PSDs) of five types of soil varying from gravel to clay were characterized using mercury intrusion porosimetry, and the measured PSDs were used to predict the soil water characteristic curves (SWCCs) for the test soils and the predictions are consistent with the SWCCs measured in the laboratory.
Abstract: To date the microporosity structures of coarse soils with various coarse/fines contents are still not fully understood. In this study, the pore-size distributions (PSDs) of five types of soil varying from gravel to clay were characterized using mercury intrusion porosimetry. The soil with a coarse content below 70% (i.e., fines content above 30%) is found to have a fines-controlled microstructure, which is sensitive to water content changes. Such soil forms a dual-porosity structure due to compaction, in which both intraaggregate pores and interaggregate pores are dominant. After saturation, the dual-porosity structure evolves into a unimodal porosity structure dominated by the intraaggregate pores. During drying, such soil exhibits a significant reduction of total volume. The soil with a coarse content above 70% instead has a coarse-controlled microstructure, which is stable upon water content changes. Such soil maintains dual-porosity structures no matter if the soil is compacted, saturated, or dried. As an example of application, the measured PSDs are used to predict the soil water characteristic curves (SWCCs) for the test soils and the predictions are consistent with the SWCCs measured in the laboratory.

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TL;DR: In this article, the authors investigated the seismic response of groups containing nonvertical piles, including the lateral pile-head stiffnesses, the "kinematic" pile deformation, and the "inertial" soil-pile-structure response.
Abstract: Several aspects of the seismic response of groups containing nonvertical piles are studied, including the lateral pile-head stiffnesses, the "kinematic" pile deformation, and the "inertial" soil-pile-structure response. A key goal is to explore the conditions under which the presence of batter piles is beneficial, indifferent, or detrimental. Parametric analyses are carried out using three-dimensional finite-element modeling, assuming elastic behavior of soil, piles, and superstructure. The model is first used to obtain the lateral stiffnesses of single batter piles and to show that its results converge to the available solutions from the literature. Then, real accelerograms covering a broad range of frequency characteristics are employed as base excitation of simple fixed-head two-pile group configurations, embedded in homogeneous, inhomogeneous, and layered soil profiles, while supporting very tall or very short structures. Five pile inclinations are considered while the corresponding vertical-pile group results serve as reference. It is found that in purely kinematic seismic loading, batter piles tend to confirm their negative reputation, as had also been found recently for a group subjected to static horizontal ground deformation. However, the total (kinematic plus inertial) response of structural systems founded on groups of batter piles offers many reasons for optimism. Batter piles may indeed be beneficial (or detrimental) depending on, among other parameters, the relative size of the overturning moment versus the shear force transmitted onto them from the superstructure.