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The piezocone penetration test (CPTu) is a common geotechnical field test to evaluate soil properties. In interpreting the CPTu field measurements, soil drainage conditions are mostly considered completely drained or undrained; however, partial drainage conditions govern for such soils as silts or clayey sand mixtures. Previous studies show that neglecting partial drainage conditions causes incorrect estimation of soil geotechnical parameters. Most studies have been conducted using calibration chambers and centrifuge tests on clayey soils. Due to the complications in modeling the piezocone test, few numerical studies have been performed under partially drained conditions, especially on coarse-grained soils. Among the challenges of numerical modeling of CPTu, one can mention the difficulty of modeling soil structure in large strain mode and soil–water interaction behavior. In this paper, piezocone penetration tests were modeled using the advanced hypoplastic constitutive model and finite-element method. The behavior of Firoozkooh sandy soil under different drainage conditions and relative densities was analyzed. Then, the effect of cone penetration on the surrounding soils was discussed. It was shown that drainage conditions and the soil relative densities significantly affected the trend of variations in excess pore-water pressure (EPWP) generated around the piezocone. [ABSTRACT FROM AUTHOR]

This study investigated the different geotechnical characteristics of soil stabilization with the addition of lime and rice husk ash (RHA) in varying amounts (3%, 5%, 7%, and 9% lime, and 4%, 8%, 12%, and 16% RHA). A series of compaction, unconfined compressive strength (UCS), California bearing ratio (CBR), pH, and X-ray diffraction (XRD) tests were performed in the laboratory to assess the impact of the considered admixtures on the stabilized soil parameters. This study also proposes the successful integration of an artificial neural network (ANN) and a Gaussian process regression (GPR) with the experimental UCS observations. The lime concentration, RHA concentration, and curing period were considered as the input parameters, and UCS was considered as the response. The proposed framework was extended to analyze the compressive behavior of treated soil on the minuscule level. Such coupled machine learning-based experimental investigation can provide deep insight into the soil behavior which otherwise would have remained unexplored due to the prohibitive nature of performing laboratory experiments on a large scale. The findings demonstrated the effectiveness of RHA in addition to lime in stabilizing the considered expansive soil. With the addition of lime and RHA mix, the UCS and CBR values of the treated soil increased significantly. [ABSTRACT FROM AUTHOR]

This paper discusses the second-order reliability-based design optimization (SORBDO) of unsaturated finite slopes. An efficient search algorithm is proposed to locate the most probable slip surfaces using the Morgenstern–Price method of slices. The variability of fitting parameters of the soil water characteristic curve (SWCC) and shear strength parameters have been taken into account for evaluating the reliability of unsaturated finite slopes. Six unsaturated shear strength (USS) models are considered for the analysis of unsaturated soils. The most conservative model for the optimum design of finite slopes is recommended. Moreover, the results indicate that the mean and standard deviation of the fitting parameters of SWCC have a significant effect on the critical centers, critical slip surfaces, and reliability index of the unsaturated finite slopes. The results demonstrate a significant change in the critical centers associated with critical slip surfaces due to the change in the mean and coefficient of variation of the fitting parameters of SWCC. Statistical analysis of the experimental data shows that a positive correlation exists between fitting parameters of SWCC related to air entry value (af) and residual water content (mf). Negative correlations are found between the fitting parameters of SWCC related to air entry value (af) and slope (nf). Similarly, the SWCC fitting parameters related to residual water content (mf) and slope (nf) have negative correlations for clayey soils. It is observed that the correlated value of the reliability index is overestimated with reference to the uncorrelated value for clayey soil slopes. The proposed design charts are beneficial for engineers and practitioners for the sustainable design of unsaturated finite slopes. Overall, the developed rigorous SORBDO framework offers a more rational approach for assessing critical failure surfaces and critical centers, considering the interdependency of random variables. [ABSTRACT FROM AUTHOR]

Several widely used field methods for estimating postliquefaction ground deformation are based on the laboratory data from one series of cyclic simple shear tests performed on one uniform clean sand reconstituted to three relative densities. It is not clear if the trends of this one data set are applicable to other clean sands, nonplastic silty sands, and nonplastic silts. A database of 579 test results on postliquefaction volumetric strain, including 299 test results that relate maximum shear strain to the factor of safety against liquefaction triggering, was compiled and used to examine trends for these soils. The database includes postcyclic test data on 10 clean sands, 2 gravels, 3 silty sands, 5 silts, and 3 clayey soils. The enlarged cyclic testing database was used to develop models that estimate postliquefaction volumetric strain and maximum shear strain as a function of soil type, state, and seismic demand. The models are applicable to uniform nonplastic soil. The state parameter was used in addition to relative density and void ratio to characterize the state of the soil. Correlations between these parameters enable the full data set to inform the models. [ABSTRACT FROM AUTHOR]

Soil suction–based analyses are paramount to proper design of foundations in expansive soils, yet availability of field soil suction profiles from direct measurement is limited. A method was developed, using directly measured suction profiles obtained from sites across the US, by which routine geotechnical tests can be used to estimate soil suction to expand the database for estimation of field suction profiles. Herein, the expanded database is used to develop best-estimate clay soil suction envelopes for boundary conditions associated with covered or uncovered ground surface subjected to natural climatic surface flux. Where appropriate for site conditions, the proposed soil suction profile envelopes can be used with any suction-based heave/shrinkage analysis. Key features of the field suction envelopes, consistent with current popular approaches, include climate-dependent estimates for equilibrium suction at depth, depth to equilibrium (stable) suction, and variation in soil suction at the ground surface. Comparisons to existing soil suction envelope recommendations are made. Finally, a limited number of cases of developed/irrigated sites are presented for comparison to soil suction profiles obtained for natural climatic surface flux conditions. [ABSTRACT FROM AUTHOR]

In most geotechnical construction works, compacted soils of cohesive-frictional nature are expected to remain mostly under partially saturated conditions and hence experience continuous changes in the suction state (negative pore-water pressure) stemming from seasonal weather and temperature variations throughout any given year. Over the last decade, a few studies have demonstrated that the suction stress characteristic curve (SSCC) can be used to describe the state of stress in partially saturated soils and therefore assess, with reasonable accuracy, the additional shear strength contribution resulting from matric or total suction. However, limited experimental data are available to conclusively verify the magnitude of suction stress at rather high values of suction, especially well beyond the residual suction. In the present work, the SSCC for compacted silty sand has been thoroughly assessed in light of recent experimental data obtained from suction-controlled triaxial testing over a wide range of matric and total suction values (0.05–300 MPa). The suction stress in the test soil was observed to increase with increasing suction even beyond the residual suction state, in contrast with findings from previous works reported in the literature for predominantly sandy or clayey soils. In addition, experimental data from suction-controlled true triaxial, ring shear, and plane strain (biaxial) tests, recently conducted on six different types of cohesive-frictional soils in the low-to-medium matric suction range, were also analyzed to obtain the corresponding SSCCs. Finally, suitable model equations are presented in order to best fit the multiple experimental data sets and hence predict the SSCC for each of the test soils under the different suction-controlled testing techniques. [ABSTRACT FROM AUTHOR]

The original paper explicitly reports that large direct shear tests were performed to quantify the shear strength of geotextile-reinforced expansive soil subgrade. The writers agree with the discusser about the critical soil mechanics of geotextile-reinforced and unreinforced expansive soil; however, in the original scope of work was limited to and focused on assessing the interface efficiency of geotextile-reinforced expansive soil. 6(b-d), which compared different configurations of the geotextile layer test sections with the unreinforced expansive soil test section. [Extracted from the article]

To study effect of plasticity on shear behavior of low-plasticity fine-grained soil, a Mississippi River Valley (MRV) silt with a plasticity index (PI) of 5.8 was treated with different dosages of sodium bentonite to modify its plasticity up to a PI of 13.5. The naturally occurring material originated from the MRV exhibited dilative behavior under normally consolidated conditions. The silt-bentonite mixtures tend to lose quasi-steady-state strength and dilative characteristics as the plasticity increased. At a PI of 13.5, the silt-bentonite mixture had plastic stress-strain clay-like behavior. Overconsolidation did not influence the friction angle of the natural silt, but for silt-bentonite mixtures with Pis of 6.2 and 9.4 the influence of prestress was evident. The normalized shear strength was significantly reduced with an increase in PI from 5.8 (natural MRV silt) to 6.0 (natural MRV silt with 2.5% bentonite added). Compared to the predictive relationships proposed by other researchers, the normalized shear strength of the natural silt was clearly higher. The critical PI was about 6 to differentiate clay-like soil and intermediate soil for the subject silt. The PI was found not to be an ideal parameter to identify the transformation of the shear behavior of the MRV silt, because the shear behavior had a big change with a slight change of PI. [ABSTRACT FROM AUTHOR]

A full-flow ball penetrometer is now routinely used in centrifuge testing for characterizing single-layer clay, silt, sand, and stratified soil samples. The behavior of the standard ball penetrometer (including the shaft) used in the field, penetrating through single and two-layer uniform clays, has recently been investigated. However, the ball penetrometers used in centrifuge testing has either a similar or higher area ratio (of the shaft to the ball) and significantly greater equivalent prototype diameter compared with the standard one used in the field. The thickness of the soil layers, however, are scaled accurately mimicking strength profiles in the field, leading to lower relative thickness of the soil layers. Large deformation finite element (LDFE) analyses were, therefore, carried out for the centrifuge ball penetrometers to investigate its performance in characterization of single- and double-layer clays. The results were validated against plasticity solutions and other previously published finite element (FE) results prior to undertaking a detailed parametric study, exploring a range of normalized soil properties and layer thickness. Three commonly used centrifuge balls were studied. For single-layer uniform clay, the area ratio of shaft to ball was shown to have significant influence on the deep bearing factors and the critical penetration depth of attaining that factor. For two-layer uniform clays, the undrained shear strength of the top layer was mostly underestimated because of the lower thickness of that layer relative to the centrifuge ball diameter. In addition, the shear strength of the bottom layer was mostly overestimated because of trapping of stiff clay at the base of the ball, advancing in stiff-over-soft clay deposits. To interpret a reference undrained strength profile, taking into account the scale effects of the penetrometer relative to layer thickness, a framework has been proposed accounting for these effects, with the LDFE data used to calibrate the framework. [ABSTRACT FROM AUTHOR]

This paper introduces a servocontrolled true triaxial apparatus that has been developed to test cubical specimens [with 7.62 cm (3 in.) sides] of unsaturated soil under controlled-suction states and for a wide range of stress paths not readily achievable in a cylindrical cell. The apparatus is a mixed-boundary-type device, with the specimen seated on top of a 5-bar high-air-entry-value (HAEV) ceramic disk and between five flexible membranes on the remaining sides of the cube. The new cell is an upgraded, more elaborate version of one previously reported by the authors, featuring two independent pore-air and pore-water pressure control systems, as well as a fully computer-driven stress application/control system. Suction states are induced in the specimens via the axis-translation technique. The paper outlines the full development of the apparatus, including its main components; assembling process; and selection of appropriate compaction method, dry unit weight, and constant-suction loading rate for clayey sand. The suitability of the apparatus is demonstrated by repeatable results from two triaxial compression tests performed on identically prepared samples of compacted clayey sand under constant 200-kPa matric suction. [ABSTRACT FROM AUTHOR]

A fundamental study of pile-soil systems subjected to lateral loads in clay soil was conducted by using experimental tests and a lateral load-transfer approach. The emphasis was on an improved wedge failure model developed by considering three-dimensional combination forces and a new hyperbolic p-y criterion. A framework for determining the p-y curve on the basis of both theoretical analysis and experimental load test results is proposed. The proposed p-y method is shown to be capable of predicting the behavior of a large-diameter pile under lateral loading. The proposed p-y curves with an improved wedge model are more appropriate and realistic for representing a pile-soil interaction for laterally loaded piles in clay than the existing p-y method. [ABSTRACT FROM AUTHOR]

It is well accepted that the quality of soft clay samples obtained using standard fixed piston samplers can be relatively poor and that block samples are necessary to yield very high quality samples. However, for many practical projects it is not economically viable or physically practical to obtain block samples. In this project, the quality of standard 54 mm composite piston samples of soft clay is examined by comparing six separate sets of 54 mm samples to parallel block sampling. Sampling and laboratory testing was carried out by three different organizations at a well characterized highly uniform soft clay site in Norway. As expected, the work showed that the block samples behaved significantly differently from those obtained using the 54 mm sampler and were of higher quality. Block sample-derived parameters were considerably different from those obtained from the 54 mm sample tests. However, significant differences were also found between the different sets of 54 mm samples. Although the differences are less than when compared with block samples, the consequences of poor quality 54 mm sampling will be significant in engineering design. It is concluded that the differences are due to small details in the sampling operation such as the need to keep the piston effectively stationary at all times, to avoid overcoring and to handle the recovered sample carefully. If a well trained driller follows good quality practice, then relatively good samples can be obtained by the fixed piston sampler, which are suitable for analysis and design of routine engineering works. [ABSTRACT FROM AUTHOR]

A new method of estimating the permeability of soils using an acoustic technique is proposed in this technical note. Biot’s coupled theory of mixtures from the mid-1950s, which addresses the relationship between the permeability of saturated soils and the characteristic frequency of elastic waves, is used. The characteristic frequency is determined from the attenuation versus frequency curves obtained by acoustic sweep tests. This study presents the experimental technique for measuring the characteristic frequency of soils and calculation procedure for estimating the permeability of sandy soils. This technical note holds discussion for silty or clayey soils. [ABSTRACT FROM AUTHOR]

A viscoplastic cap model of the Perzyna type was developed for simulating high strain rate behaviors of soils. An associative viscous flow rule was used to represent time-dependent soil behaviors. The viscoplastic cap model was validated against experimental data from static and dynamic soil tests. The model was also compared with soil behaviors under creep and stress relaxation with good agreement. However, the model was unable to represent tertiary creep where strain softening became significant. The model was subsequently integrated into LS-DYNA for finite-element simulations of high strain rate behaviors of sandy and clayey soils in explosive tests. The significance of strain rate effect on the soil responses is presented herein. It is concluded that the viscoplastic cap model is adequate for simulations of soil behaviors under high strain rate loading, creep, and stress relaxation, covering a wide range of time-dependent problems. [ABSTRACT FROM AUTHOR]

The potential of woodash to stabilize clay soil was evaluated. The evaluation involved the determination of the geotechnical properties of clay soil in its natural state as well as when mixed with varying proportions of woodash. The parameters tested included the particle size distribution, specific gravity, Atterberg limits, compaction characteristics, California bearing ratio (CBR) and the compressive strength. The CBR and strength tests were repeated after 28-day curing of the treated samples. Results showed that the geotechnical parameters of clay soil are improved substantially by the addition of woodash; plasticity was reduced by 35% and CBR and strength increased by 23–50% and 49–67%, respectively, depending on the compactive energy used. The highest CBR and strength values were achieved at 10% woodash. Results also showed that curing improved the strength of the woodash-treated clay. However, the strength gain was short lived as the strength quickly decreased after 7–14 days of curing. These results imply that although woodash provides some of the beneficial effects of lime in soil stabilization, such as plasticity and swell reduction, improved workability, and strength increase, it is unlikely to be a substitute for lime as strength gain is short lived. [ABSTRACT FROM AUTHOR]

Lime continues to be one of the most popular chemical admixtures used to modify expansive clays despite the associated mixing and pulverization problems. In the present investigation, the efficacy of CaCl2 in place of conventionally used lime is studied by conducting laboratory and field tests. These investigations were carried out on the slopes of a trapezoidal trench made in expansive clay bed. Heave measurements were taken on the lime and CaCl2 treated slopes and also on untreated slopes for four consecutive cycles of wetting and drying. The field cyclic seasonal movements and the subsequent laboratory tests on undisturbed and disturbed soil samples revealed that the CaCl2 could be a promising chemical modifier instead of conventionally used lime, not only due to its multifold influence on heave control, plasticity reduction, and swell properties but also its easy application in the form of solution without any need for pulverization and mixing. Though an apparent reduction in unconfined compressive strength of treated samples is observed, the drained triaxial tests on treated and untreated samples revealed that there is an increase in the angle of internal friction of treated samples. [ABSTRACT FROM AUTHOR]

This paper presents a case history describing measurements made during the installation and load testing of groups of five, closely spaced, precast concrete piles in a soft clay-silt. The test results extend the presently limited set of reported high-quality data for pile groups at field scale and allow assessment of the reliability of existing numerical and analytical predictive approaches. Full scale maintained compression and tension load tests on groups as well as tests on single (reference) piles and an individual test on a pile within a pile group enable the effects of multiple pile installations and interaction between piles under load to be assessed. The results are compared with existing simple methods of pile group analysis and with other case histories reporting results on small pile groups. A simple expression to evaluate pile group stiffness efficiency is proposed. [ABSTRACT FROM AUTHOR]

The present contribution reports on a mixed numerical experimental study of the time dependent processes in saturated soils with reference to isotropic consolidation. Owing to its relative simplicity, isotropic consolidation is often viewed as a basic tool for inferring the material parameters of various constitutive models. Within this modeling framework, the paper advocates the use of critical state models for an accurate description of the time dependent deformation of clayey soils. Material models, in which the critical state model applies only to the subcritical region, have been also addressed. Examples include models where the supercritical region is cut off, e.g., by a Mohr–Coulomb surface. Starting with the modified Cam clay model, as a classical representative, the paper revisits a simple isotropic consolidation test. It is suggested that such a conventional laboratory experiment, when combined with a suitable optimization procedure, is sufficient in deriving the desired material parameters, including the initial void ratio, deformation dependent variation of the coefficient of permeability and the preconsolidation pressure representing here an important measure of the structural strength of soils. Several numerical and experimental results are presented to support the theoretical grounds. [ABSTRACT FROM AUTHOR]

A review of the article "Shear Strength of Clay at Different Shear Rates," by Ivan B. Gratchev and Kyoji Sassa, is presented.

A review of the article "Shear Strength of Clay at Different Shear Rates," by Ivan B. Gratchev and Kyoji Sassa, is presented.

The article presents comment on the study that determines the effect of microfabric on undrained static and cyclic behavior of kaolin clay. It recognizes the method used by the authors in using different techniques to identify the microfabric of clays, which also require enough experience to accurately interpret results. It also commends the authors for successfully demonstrating that soil with flocculent fabric exhibits higher shrinkage limit than those with dispersed limit.

The article provides an overview on the evaluation of cyclic softening in silts and clays. The authors details the occurrence of sands to clays that take place around a plasticity index (PI) of 7. One author suggests the slightly higher values of PI to define the transition of sands to clays. The author also prefers a slightly higher PI criteria to define claylike behavior (PI>10) as sandlike soils and the simplified methodology requires a certain level of conservation in its application for low to moderate risk projects. Moreover, three different approaches are suggested on the estimation of the cyclic resistance ratio (CRR) for claylike fine-grained soils in the field.