Journal of Geotechnical and Geoenvironmental Engineering

Experiments were conducted to evaluate cation exchange during hydration of geosynthetic clay liners (GCLs) used in composite hydraulic barriers and the effect on their hydraulic conductivity. GCLs arranged in a composite barrier configuration were hydrated by contact with moist compacted subgrades (two clays, one silt, and one sand) under a confining stress of 10 kPa for 30 days to 1 year. No measurable exchange occurred in GCLs hydrated for 30 days. For hydration periods longer than 30 days, the exchange increased as the duration of hydration increased. The exchange during subgrade hydration had no measurable effect on the hydraulic conductivity to deionized (DI) water. However, if the GCL was desiccated after hydration, the hydraulic conductivity increased more than 1,000-fold. Dissolution of calcite within the bentonite during permeation with DI water also induced the replacement of sodium by calcium; however, this additional exchange had no measurable effect on the hydraulic conductivity to DI water. Data from two case histories indicate that calcium and/or magnesium in the subgrade, or in calcite within the GCL, eventually will replace nearly all sodium in GCLs used in composite barriers. The data also indicate that cover soil should be deployed expediently on composite barriers with GCLs to prevent wet-dry cycling and corresponding impacts on hydraulic conductivity.

The aim of this study is to assess experimentally the volume change behavior of geosynthetic clay liners (GCLs) under elevated temperatures. Such elevated temperatures can be generated in landfills as the result of biological decomposition of organic matter in municipal solid waste. A modified consolidometer capable of handling temperatures up to 60°C was utilized for this purpose. A series of thermomechanical consolidation tests were performed on two different GCLs at different elevated temperatures, varying from 20 to 60°C, and different vertical stress levels (50, 100, and 150 kPa). The results show that the thermally induced volume change is stress dependent. A preliminary conceptual explanation for this behavior is introduced and discussed in this study.

The current study examines and quantifies the limit shaft resistance of drilled shafts installed in clay through finite-element analyses that use an advanced two-surface-plasticity constitutive model for clay. The clay constitutive model used in this study reproduces the mechanical response of clays under multiaxial loading conditions, predicts both drained and undrained behavior at small and large strains, and captures the drop in strength toward a residual value at very large shear strains. One-dimensional finite-element analyses are performed to simulate the essential stages of the installation and loading of drilled shafts in clay for different initial stresses, different overconsolidation ratios, and different values of the difference between the critical-state and the minimum residual friction angles. On the basis of these simulations, equations for the shaft friction coefficient are proposed that can be used in the calculation of the shaft resistance of drilled shafts in clay. Predictions using the proposed equations compare well with the data derived from different field pile load tests on drilled shafts.

The beam-on-Winkler foundation (BWF) method is a popular analysis approach for computing the lateral pile response resulting from both inertial and kinematic loading. However, there is significant uncertainty regarding how to properly represent the load-resistance (i.e., $p\text{-}y$) behavior of liquefied soils. This confusion stems from the significant variability observed with the phenomenon and the large number of $p\text{-}y$ spring models for liquefied soils that have attempted to account for that variability. In an attempt to develop a practical but broadly applicable approach, a simplified hybrid $p\text{-}y$ spring model is presented. This hybrid model incorporates aspects of existing $p\text{-}y$ spring models for liquefied soil and is applicable to a wide range of soil types, relative densities, pile/shaft diameters, and loading conditions. Comparisons with a variety of published case histories involving single piles indicate that the hybrid $p\text{-}y$ spring model provides reasonable estimates of response for both kinematic and inertial loadings. For approximately 80% of the evaluated loading scenarios, the computed maximum bending moments and the peak pile head displacements were within ±30 and ±25%, respectively, of the measured values. The proposed hybrid $p\text{-}y$ model generally overestimated peak bending moments when considering kinematic loading but tended to underestimate peak bending moments for relatively low loads when considering inertial loading. For computed head displacements less than about 20 cm (7.9 in.), computed head displacements were within ±2.54 cm (1 in.) of measured displacements. For computed head displacements greater than about 20 cm (7.9 in.), head displacements were overestimated in approximately 80% of the loading scenarios.

Although evidence in the literature indicates that the lateral $p\text{-}y$ resistance of piles in liquefiable soils is significantly reduced, the shape and amplitude of the reduced $p\text{-}y$ curve during pore pressure buildup are needed for reliable design of pile foundations. To investigate this issue, a single steel pile embedded in homogeneous saturated Nevada sand was subjected to sequential dynamic shaking and lateral (inertial-equivalent) loading. A key goal in the test program was to develop a data set capable of rendering insight into the characteristics of $p\text{-}y$ resistance under developing liquefied soil conditions. As such, results presented focus primarily on the static $p\text{-}y$ curves backcalculated from bending moment distributions at the achieved excess pore pressures. Analysis of the experimental data shows that mobilization of the partially liquefied soil was achieved during lateral loading. A rich set of test data was produced from this testing series, which will be useful for model validation and subsequent design efforts.

Implementation of laboratory-tested biomediated soil improvement techniques in the field depends on upscaling the primary processes and controlling their rates. Microbial-induced carbonate precipitation (MICP) holds the potential for increasing the shear stiffness and reducing the hydraulic conductivity by harnessing a natural microbiological process that precipitates calcium carbonate. The study presented herein focuses on controlling MICP treatment of one-dimensional flow, half-meter-scale column experiments. Treatment was optimized by varying procedural parameters in five pairs of experiments including flow rates, flow direction, and formulations of biological and chemical amendments. Monitoring of column experiments included spatial and temporal measurements of the physical, chemical, and biological properties essential to the performance of MICP, including shear wave velocity, permeability, calcium carbonate content, aqueous calcium, aqueous ammonium, aqueous urea, and bacterial density. Relatively uniform improvement of a half-meter one-dimensional flow sand column experiment resulted in a change from a shear wave velocity of 140 m/s to an average of 600 m/s. Examination of data sets provides insight into which parameters have a first-order effect of MICP treatment uniformity and efficiency and how these parameters can be monitored and controlled.

The mechanisms that control the seismic liquefaction performance of shallow foundations are identified for the special, still common case of a clay crust separating the foundation from the liquefied ground. For that purpose, foundation response is first analyzed with the nonlinear dynamic finite-difference method and consequently evaluated in connection with published field and experimental evidence. Insight is given into the excess pore-pressure buildup under the foundation, the seismic settlement accumulation, the static-bearing capacity degradation, and the inertia-induced interaction with the superstructure. It is thus shown that a naturally or artificially created nonliquefiable soil crust may effectively mitigate the detrimental effects of liquefaction and allow for a performance-based design of surface foundations, without additional improvement measures.

Damage in buildings caused by excavation-induced ground displacement is a major concern in any underground work of an urban area. To predict the building damage, it is generally assumed the onset of visible cracking is associated with the limiting or critical tensile strain of the structure. The present analytical models of calculating tensile strains analyze individual walls of the building as elastic deep beams. Because of the two-dimensional nature of these methods, the walls are assumed to be perpendicular to the excavation axis. To obtain the maximum tensile strain, only in-plane movements are considered, whereas the effects of three-dimensional displacements such as twist are ignored. In this study, the building is represented as a simply supported rectangular elastic thick plate. The relationship between the state of tensile strain and the onset of visible cracking is applied to the plate theory. The building damage criteria based on critical displacement parameters, namely deflection ratio, horizontal strain, and twist, are proposed. A number of case studies of damaged buildings are used to assess the ability of this procedure to predict the degree of damage. The new plate model obtained the most number of accurate predictions compared with the other beam models.

The strength variability of soils improved by lime-cement columns is very high, and assessment of the reliability is associated with high uncertainty. Previous research on natural soils has shown that variability has a major impact on the reliability of geotechnical systems. However, concerning ground improvement with lime-cement columns, the effect of the uncertainties associated with improved strength properties on the reliability is unknown. This paper addresses the integration of reliability-based design in the design of embankments founded on soil improved by lime-cement columns by an analysis of a project conducted in Sweden. The uncertainties associated with estimating the strength property based on results from cone penetration tests and their effect on the assessed system reliability are addressed and discussed. The use of variance reduction with respect to the spatial variability of the shear strength of the columns was found to have a major influence on the assessed system reliability. Furthermore, it was found that the transformation uncertainty from measurements based on cone penetration tests has a significant impact on the assessed system reliability. System reliability cannot be improved significantly simply by performing a large number of tests.

With the objective of better and more environmentally friendly recycling methods, many researchers are now examining the use of scrap tires as a new geomaterial. Based on past research, it was clear that tire chips reduce the rise of excess pore-water pressure when subjected to earthquake shaking. Based on such characteristics, online pseudodynamic response tests were conducted in this study on model grounds consisting of either tire chip-mixed sand or alternating layers of sand and tire chips with the aim of clarifying the seismic response characteristics of tire chips and tire chip-sand mixtures. Online testing is a method of feeding soil response characteristics directly from soil samples into a one-dimensional modeling algorithm. The test results showed that when tire chips with low stiffness were either mixed with sand or placed as layers, more significant damping and seismic isolation effects were observed. The presence of tire chips also reduced the accumulation of excess pore-water pressure in the layer, preventing the occurrence of liquefaction. In addition, when tire chips are installed as layers beneath the sand, liquefaction is not generated in the upper sandy layer because the amplitudes of the seismic waves are attenuated. Finally, the effectiveness of tire chips mixed with sand increased as the mix ratio was increased. When they were installed as pure layers, tire chips were more effective when placed at a deeper location or when the layer was thicker.

This paper presents the results of an experimental study on Leda clay-concrete interface shear behavior. Leda clay specimens with various dry densities and salt contents are used to study the influence of these parameters on the interface shear behavior. The results indicate the following: (1) interface shear resistance increases as the concrete surface roughness increases; (2) increasing the dry density of remolded Leda clay enhances its interface shear resistance; and (3) a higher salinity of Leda clay pore water results in higher interface shear strength.

Response surface methods (RSMs) are attractive approaches for slope reliability analysis because such methods can integrate deterministic numerical slope stability evaluation and reliability analysis. For a slope in layered soils, its performance function is generally nonlinear and the system failure probability could be larger than the failure probability of the most critical slip surface. In this study, the applicability of the kriging-based RSM for system reliability of soil slopes is assessed through its application to two slopes with obvious system effects. It is found that the kriging method combined with Monte Carlo simulation (MCS) can deliver accurate system failure probability estimation. For comparison, the classical RSM based on the iterative local approximation of the performance function may fail to detect the most critical slip surface. The classical RSM can only calculate the failure probability of one slip surface even if the first-order reliability method or MCS is used. Even when the same calibration samples are used, the second-order polynomial-based RSM is not as accurate as the kriging-based RSM. The results in this study show that the kriging-based RSM is an advantageous and promising approach for calculating the system reliability of soil slopes.