International Journal of Geomechanics

Two new constitutive models formulated within the framework of kinematic hardening plasticity are presented and their implementation into a finite-element program is described. The models are extensions of two existing constitutive models for reconstituted clays and introduce a number of kinematic surfaces within the modified CAM clay bounding surface. The new key feature of the models is a hardening modulus which results in a smooth variation of stiffness with strain, from the high elastic value, within the first kinematic surface, to the value on the bounding surface. Other features include a mathematical formulation of the models in general stress space to facilitate their implementation into a finite-element program, a variety of shapes of the yield and plastic potential surfaces in the deviatoric plane, and the novel concept of changing the active yield surface, which is necessary for the consistent formulation and implementation of the models into a finite-element code. The models are shown to have the ability to reproduce realistically the observed nonlinear prefailure behavior of overconsolidated clays in the small strain range.

Detection of contacts between three-dimensional (3D) blocks is a key problem in three-dimensional distinct element analysis. In this paper, the limitations of the $c$ – $p$ method are discussed. The writers have also put forward the “penetration edges method” for the detection of contacts in 3D blocks system. The contact relations between two 3D blocks are classified into seven types and 3D contact detection is determined by the contact type. The principle of this new approach is simple to implement and can overcome the limitation of the $c$ – $p$ method as discovered in this study. Limited case studies have indicated that the present algorithm is as efficient as the $c$ – $p$ method but is free from the limitation of this method.

Expansive soils cause important economical losses in many arid or semiarid countries in the world. Considering the large economic impact, relatively few efforts have been devoted to develop analytical methods that may help practitioner engineers to adequately design civil infrastructure on this type of soil. A rational design method should be able to quantify the heave or subsidence of the soil associated with the suction changes during water diffusion, as well as the contact pressures on soil-structure interfaces. Accordingly, in this and in a companion paper, the problem of volume changes due to nonpermanent water flow in expansive soils is studied and applied to the case of vertical moisture barriers. In this paper, a constitutive model for expansive soils is proposed. This model is an extension of that developed by Alonso et al. in 1990, in the sense that it can take into account the behavior of expansive soils. The advanced model is evaluated by comparing the numerical results with experimental data.

Several alternatives have been proposed to prevent damage to civil infrastructure founded on expansive soils. For example, deep moisture barriers have been used in highways and buildings. However, in some cases, the protected lanes or structures degrade to similar levels as the unprotected ones, although at a smaller rate. In spite of these poor results, relatively few efforts have been devoted to the development of analytical methods for rational designs on expansive soils. This paper couples the constitutive model for expansive soils developed in the companion paper with flow equations in a deforming medium and a finite element code is developed. The resulting numerical tool has the capacity of computing soil suction and volumetric strain changes of expansive soils under a defined wetting–drying regime. To verify the capabilities of this computer code, a laboratory barrier model was built. The model was instrumented to measure soil suction changes and the corresponding surface displacements. The experimental and theoretical results were compared. Finally, the numerical model was applied to a design example of a deep moisture barrier.

The paper presents a case study for numerical analysis of the consolidation behavior of an instrumented trial embankment constructed on a soft soil foundation. Details are given to the geological profile, field instrumentation, laboratory test results, and determination of soil parameters for numerical modeling. Embankment settlement is estimated based on one-dimensional consolidation analysis and nonlinear finite-element analysis following Biot’s consolidation theory. Finite-element results are calibrated against the measured field data for a period of more than $3\text{years}$ . Development and dissipation of excess pore pressure, long-term settlement, and horizontal displacement are predicted and discussed in light of sensitivity of embankment performance to some critical factors through a parametric study.

We propose three-dimensional linear and simplified nonlinear soil response methods based on an input seismic wave field. An input wave field is employed to treat seismic surface waves excited by a deep structure in a shallow soil model. First, the linear method is applied to a hard- and a soft-soil site located in Mexico City, and soil responses excited by $S$ -, surface-, and whole-wave fields reproduce the input waves fields well. Then, the linear method is applied to estimate soil responses for three large earthquakes at two soft-soil sites located in the reclaimed zone of Tokyo Bay, and again it works well. Finally, we attempt to perform nonlinear and liquefaction soil response analyses in the reclaimed zone, on the basis of an input wave field modified according to varied soil properties. The nonlinear method seems to provide reasonable nonlinear and liquefaction soil responses.

The behavior of sand on the $\pi$ plane, including the relation between the principal deviatoric strain increment ratios, is not fully understood. The objectives are: To clarify experimentally the relation between the principal deviatoric strain increment ratios for sand in a wide range of $b$ values and to discuss the basic shear behavior, taking particular notice of inherent transverse isotropy and noncoaxiality. From the experimental results on sand with inherent transverse isotropy, it was observed that the relation between the principal deviatoric strain increment ratios is fundamental and is related to the shape of the failure surface and the extent of strain localization. A new equation for the principal deviatoric strain increment ratios is proposed to model the influence of the incremental stress.

Although horizontal directional drilling has become commonplace, there are problems associated with high drilling mud pressures causing hydraulic fracture leakage of mud out into the environment. Initiation of tensile fracture is examined here, using finite- element analysis to represent the sand material and the annulus of filtercake that forms around the borehole. The analyses examine the soil response as mud pressures are increased, including shear failure in the sand material and the cohesive filtercake layer. The study identifies the initial geostatic stress conditions and the drilling fluid pressures that initiate tensile stresses in the filtercake. The effects of filtercake thickness, borehole depth, and the location of the maximum tensile stresses are studied. Significant discrepancies are found relative to limits currently used in the industry. Tensile fracture may be responsible for some mud loss, but simple use of drilling mud pressures that prevent tensile circumferential stress may be overly conservative.

An efficient and practical method of analysis to predict the effects of tunneling on existing single pile foundations is described. The method involves a combination of the finite- and boundary-element (FAB) methods, with free-field ground movements predicted by the finite-element method and the response of an embedded pile to these ground movements predicted by the boundary-element method. The method allows prediction of the full three-dimensional (3D) response of the pile as tunnel excavation proceeds towards the pile and away from it. Very good agreement is obtained between predictions of the pile response obtained by the FAB method and a 3D finite-element analysis which specifically includes the pile in the finite-element mesh. The vastly superior computational efficiency of the FAB method over the full 3D finite element approach is also illustrated.