Journal of Geotechnical and Geoenvironmental Engineering

This paper presents the results of centrifuge model tests on unstrutted deep excavation in dense sand and its influence on an adjacent single pile foundation behind the retaining wall. It is found that, in the case of a stable wall, the induced pile bending moment and deflection decrease exponentially with increasing distance between the pile and the wall. Pile head boundary condition plays an important role in affecting the pile responses due to an adjacent excavation. In the case of retaining wall collapse, the failure pattern of the soil behind the wall features a slip plane projecting from near the wall toe to the ground surface. Soil within the failure zone demonstrates large lateral movement and induces significant bending moment and deflection on pile located within the zone. Soil movement and pile responses outside this zone are noted to be significantly less. A comparison between the experimental results and the theoretical predictions by an existing numerical method shows good agreement, provided that appropriate assumptions are made on the soil parameters and conditions, especially in the case of retaining wall collapse.

In this paper, a nonlinear continuum method is developed to predict the load-displacement response of drilled shafts under lateral loading. The method can consider drilled shafts in a continuum consisting of a soil layer overlying a rock mass layer. The deformation modulus of the soil is assumed to vary linearly with depth, and the deformation modulus of the rock mass is assumed to vary linearly with depth and then to stay constant below the shaft tip. The effect of soil and/or rock mass yielding on the behavior of shafts is considered by assuming that the soil and/or rock mass behaves linearly elastically at small strain levels and yields when the soil and/or rock mass reaction force p (force/length) exceeds the ultimate resistance p_ult (force/length). For the calculation of the ultimate resistance p_ult of the soil, methods that are available in the literature are used. To calculate the ultimate resistance p_ult of the rock mass, a method based on the Hoek-Brown strength criterion is proposed. The proposed method is verified by comparing its results with available elastic solutions and field test data, and it is finally applied in the design of a bridge foundation in Massachusetts.

The 3D passive earth pressure problem is investigated by the upper-bound method in limit analysis. Three kinematically admissible failure mechanisms referred to as M1, Mn, and Mnt are considered for the calculation schemes. The M1 mechanism is an extension into three dimensions of the classical 2D Coulomb mechanism. The Mn mechanism is a generalization of the M1 mechanism and is composed of a sequence of rigid blocks. Finally, the Mnt mechanism is a more elaborate mechanism in which the final block of the Mn mechanism is truncated by two portions of right circular cones. The lowest upper-bound solutions given by the present analysis are compared with other authors' results and presented in a form of design tables relating the geometrical parameters, soil properties, and the 3D passive earth pressure coefficients.

In situ ground freezing with liquid nitrogen can be an excellent technique for obtaining high quality undisturbed samples from a wide range of loose sand deposits, with their in situ conditions preserved. This paper describes the techniques used during the CANLEX project to carry out in situ ground freezing and undisturbed sampling of the loose sand deposits encountered at six test sites. Specific details, with respect to the effects of difficult subsoil or ground-water conditions encountered at the sites, are provided. Modifications made to the ground freezing and sampling system to accommodate difficult ground conditions are described. The actual advance of the freezing front and the consumption of liquid nitrogen are compared with theoretical predictions. The dry coring technique utilized to recover undisturbed frozen sand samples is described. The void ratios measured for the frozen core samples are compared with void ratio measurements obtained using geophysical logging in boreholes located within a 5-m radius of the freeze pipe. The costs associated with in situ ground freezing utilizing liquid nitrogen and coring of the frozen sand at six test sites are presented.

Constant-head hydraulic conductivity tests are performed on layered heterogeneous porous media to evaluate the use of underdrains to calculate the hydraulic conductivity of an overlying, less permeable medium. The layered profiles consist of a barrier layer comprising sand mixed with 10% kaolin, overlying a foundation layer comprising sand mixed with only 5% kaolin. Underdrains are evaluated by replacing excavated portions of the foundation layer with only sand. The results indicate that preferential flow of water occurs around, rather than through, the sand underdrains resulting in an underestimate of the measured hydraulic conductivity of the barrier layer assuming 1D, saturated flow in accordance with standard practice. The observed preferential flow effect is consistent with previously published numerical simulations of unsaturated flow through similarly layered heterogeneous soil profiles that indicate lateral flow around underdrains due to the contrast in unsaturated properties of the soils. The results of this study have important ramifications with respect to the use of underdrains to measure in situ hydraulic conductivity of compacted clay liners for waste containment.

Earthquake-induced sliding displacements of earth structures are generally evaluated using simplified sliding block analyses that do not accurately model the seismic response of the sliding mass nor the seismic forces along the slide plane. The decoupled approximation introduced to capture each of these effects separately is generally believed to be conservative. However, recent studies using linear viscoelastic sliding mass models have revealed instances where the decoupled approximation is unconservative. In this paper, a coupled analytical model that captures simultaneously the fully nonlinear response of the sliding mass (necessary for intense motions) and the nonlinear stick-slip sliding response along the slide plane is presented. The proposed sliding model is validated against shaking table experiments of deformable soil columns sliding down an inclined plane. The effect of sliding on the response of earth structures is evaluated, and comparisons are made between sliding displacements calculated using coupled and decoupled analytical procedures with linear and nonlinear material properties. Nonlinearity resulting from stick-slip episodes is often the dominant source of nonlinearity in this problem. The decoupled approximation was unconservative primarily for intense ground motions for systems with low values of k_y, larger values of k_y/k_max, and high period ratios (T_s/T_m). Results indicate that a decoupled analysis is adequate for earth structures that are not expected to experience intense, near-fault motions. However, for projects undergoing intense, near-fault ground motions, a fully nonlinear, coupled stick-slip analysis is recommended.

A simplified procedure using shear-wave velocity measurements for evaluating the liquefaction resistance of soils is presented. The procedure was developed in cooperation with industry, researchers, and practitioners and evolved from workshops in 1996 and 1998. It follows the general format of the Seed-Idriss simplified procedure based on standard penetration test blow count and was developed using case history data from 26 earthquakes and >70 measurement sites in soils ranging from fine sand to sandy gravel with cobbles to profiles including silty clay layers. Liquefaction resistance curves were established by applying a modified relationship between the shear-wave velocity and cyclic stress ratio for the constant average cyclic shear strain suggested by R. Dobry. These curves correctly predicted moderate to high liquefaction potential for >95% of the liquefaction case histories and are shown to be consistent with the standard penetration test based curves in sandy soils. A case study is provided to illustrate application of the procedure. Additional data are needed, particularly from denser soil deposits shaken by stronger ground motions, to further validate the simplified procedure.