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The use of p-multipliers in the analysis of the lateral loading behavior of pile groups is based on the concept of modifying the single-pile p-y curve to obtain the p-y curve for a pile in a group. The p-multipliers account for the reduced soil resistance mobilized at a given deflection as a result of overlapping of shear zones. Different factors can influence the p-multipliers; however, because of the lack of experimental data, most researchers and design guidelines consider only the normalized pile spacing in the direction of loading in their recommendations. In this study, the effects of pile spacing and clay stiffness on the p-multipliers were investigated using the results of two series of centrifuge tests. The soil profile consisted of four lightly overconsolidated clay layers overlying a dense sand layer. The pile groups had a symmetrical layout consisting of 2 × 2 piles spaced at center-to-center distances of 3.0 and 7.0 pile diameter (D) and were driven into improved (stiff clay) and unim...

Recent laboratory tests and field observations have revealed that unsaturated sands are susceptible to liquefaction. Systematic investigation of liquefaction potential of unsaturated sands is, however, lacking. In this paper, a coupled hydromechanical elastoplastic constitutive model for unsaturated sands is calibrated using available laboratory test results. A parametric study is then conducted using the calibrated constitutive model to investigate the effects of initial degree of saturation, relative density, and effective confining pressure on the liquefaction resistance of unsaturated sands. The results suggest that the liquefaction resistance of unsaturated sands increases with decreasing degree of saturation and increasing relative density and effective confining pressure. The results also reveal that the effect of degree of saturation on liquefaction resistance is more pronounced near 100% degree of saturation. The results of the parametric study are then condensed to create a design chart ...

A uniform gradient (UG) element formulation for a four-node quadrilateral element is derived and implemented for solving the fully coupled governing equations for the dynamics of a saturated porous medium. An hourglass control scheme is also derived for eliminating the hourglass modes that arise when using the UG element formulation. The effectiveness of the new formulations is investigated by simulating the quasi-static and dynamics response of a footing and the dynamic response of an earth dam. The results show that the level of excitation of hourglass modes is problem-dependent and mesh-dependent. The proposed method for controlling the hourglass modes is shown to be effective with minimal effect on the computed response.

This paper proposes an analytical approach predicting the development and progress of the plastic zone around a wellbore drilled in linear hardening or softening Drucker-Prager rocks in a theoretically consistent way. With some reasonable assumptions and simplifications on the definitions of stress invariants as well as the equivalent plastic strain, the wellbore boundary value problem is fully linearized, which leads to a simple ordinary differential equation with the radial displacement being the basic unknown. Explicit solutions for the stress and displacement fields due to wellbore drilling can thus be easily obtained. Comparisons between the analytical solution and the ABAQUS numerical simulation verify the reliability and applicability of the present closed-form solution. Extensive numerical results for the tangential and radial stress distributions are then provided to explore the influences of the friction angle and the plastic tangential modulus, for both strain hardening and softening ca...

Following the comprehensive model formulation given in Part I, a fully implicit integration procedure for the rate equations using a closest point projection method is presented in this paper. The stress-update algorithm and calibration procedure for all the model parameters are discussed in detail. Two sets of laboratory test results, one from unsaturated Minco silt and another one from Toyoura sand, are used to validate the proposed model. The model is shown to have the ability to capture the coupling effects between hydro- and mechanical behavior and predict the laboratory tests reasonably well.

Unsaturated soils are three-phase porous media consisting of a solid skeleton, pore water, and pore air. The behavior of unsaturated soils is strongly influenced by the matric suction (pore air pressure minus the pore water pressure). Soil water characteristic curves (SWCCs) describe the relationship between matric suction and water content in unsaturated soils and, therefore, capture the hydro-behavior of soils. SWCCs show hysteretic behavior that not only depends on the wetting or drying history of the soil, but also on the stress-strain history (mechanical behavior) of a soil. The hydro-behavior of unsaturated soils, on the other hand, influences the mechanical behavior through matric suction. To predict the behavior of unsaturated soils, a hysteretic SWCC model is proposed based on the bounding surface plasticity concept. The model for hysteretic SWCCs is then incorporated into a constitutive model for unsaturated sands and silts in the general stress space. The resulting model is a comprehens...