Journal of Geotechnical and Geoenvironmental Engineering

This study considers the shaking-induced displacement and dynamic response of a rigid block and deformable columns of soil on an inclined plane. This work demonstrates that because of the coupled dynamic response and sliding of earth masses, actual deformations in these systems can vary significantly from those computed in a rigid block analysis proposed by Newmark in 1965. The rigid sliding block procedure was found to be generally unconservative when the predominant frequency of the input motion is somewhat less or about equal to the natural frequency of the sliding mass $(0.2⩽\mathrm{tuning}\mathrm{ratio}⩽1.3)\text{.}$ Conversely, the sliding block procedure is generally conservative when the predominant frequency of the input motion exceeds the natural frequency of the mass $\left(\mathrm{tuning}\mathrm{ratio}>1.3\right)\text{.}$ While it was found that sliding surfaces might limit transmission of energy, high inertial forces can, nonetheless, develop in a sliding mass because of its stick–slip dynamic response. This was found to occur in many of the soil column tests when accelerations in excess of the yield acceleration were measured at the base of the sliding mass. Based on the results of this study, recommendations are made to aid practitioners in selecting an appropriate seismic slope deformation procedure.

In the last three decades, barrettes, namely, excavated rectangular piles, have been increasingly used as foundations to resist large vertical and significant horizontal loads. Empirical approaches are commonly used for the design analyses of barrettes, due to insufficient understanding of the fundamental behavior of the barrettes. In order to improve current design analysis, the behavior of the shaft resistance of long barrettes (ranging from 36 to 63 m long) under vertical loading is investigated in this paper. Fifteen well-documented and reliable tests on long rectangular barrettes founded in granitic saprolites in Hong Kong are selected for critical review and analysis. A database is compiled from these tests. The writers were heavily involved with the construction, testing, and analysis of three of the 15 barrettes. The barrette shaft resistance is quantitatively analyzed with respect to local displacements, in situ soil properties, and the effective stress principle. In addition, the effects of construction including grouting, construction time, side scraping, and excavation tools on the mobilization of the barrette shaft resistance are also investigated. For the barrettes considered, a minimum local displacement of 20 mm is required to mobilize the side resistance of barrettes fully. Grouting along the shaft of barrettes improves the side resistance. On the contrary, construction time has an adverse effect on the shaft resistance, possibly resulting in 45% reduction in capacity if there is a long period of standing time prior to concreting.

Keyblock stability in the “Snake Path” cliff of the Masada monument, situated on the western margin of the seismically active Dead Sea transform, is studied using field mapping, mechanical analysis, and monitoring of displacement, pressure, temperature, and relative humidity, over a period of 11 months. A linear nonreversible displacement trend is interpreted as the block response to regional microseismicity. A more pronounced cyclic displacement trend however is shown to be a response to climatic changes on the cliff face. This finding introduces a new, time-dependent, failure process in jointed rock slopes—the degradation of shear and/or cohesive strength of joints due climatic effects. Using two-dimensional (2-D) and three-dimensional (3-D) limit equilibrium analyses it is demonstrated that the 2-D solution overestimates the factor of safety against sliding by as much as 15% if water pressures in the boundary joints are considered. Application of a 2-D solution for a truly 3-D case where prismatic blocks are considered proves therefore to not be conservative.

Large vertical (axial) and lateral loads often act on the heads of drilled shafts in jointed rock. In current design practice, the $p-y$ curve method used in design of laterally loaded drilled shafts in soil is often also used for shafts in jointed rock. The $p-y$ curve method treats the soil as a continuum, which is not appropriate in jointed rock, particularly when failure occurs due to sliding on joints. A new discontinuum model was developed to determine the lateral load capacity of drilled shafts or piers in a jointed rock mass with two and three joint sets. It consists two parts: a kinematic and a kinetic analysis. In the kinematic analysis, Goodman and Shi’s block theory is expanded to analyze the removability of a combination of blocks laterally loaded by a pier. Based on the expanded theory, a method was developed to select removable combinations of blocks using easily constructed two-dimensional diagrams. In the kinetic analysis, each kinematically selected removable combination of blocks is examined with the limit equilibrium approach to determine the ultimate lateral load capacity. Although the procedure is similar to slope stability analysis, it is more complicated with the addition of a lateral force and the vertical load exerted by the pier. Simple analytical relations were developed to solve for the ultimate lateral load capacity.

A procedure is proposed to evaluate the triggering of liquefaction in ground subjected to a static shear stress, i.e., sloping ground, using the yield strength ratio, $s_u\left(\mathrm{yield}\right)/{\sigma }_{\mathrm{v0}}^{\prime }\text{.}$ Thirty liquefaction flow failures were back analyzed to evaluate shear strengths and strength ratios mobilized at the triggering of liquefaction. Strength ratios mobilized during the static liquefaction flow failures ranged from approximately 0.24 to 0.30 and are correlated to corrected cone and standard penetration resistances. These yield strength ratios and previously published liquefied strength ratios are used to develop a comprehensive liquefaction analysis for ground subjected to a static shear stress. This analysis addresses: (1) liquefaction susceptibility; (2) liquefaction triggering; and (3) post-triggering/flow failure stability. In particular, step (2) uses the yield strength ratio back-calculated from flow failure case histories and the cyclic stress method to incorporate seismic loading.

Short-term undrained stability often controls the design of braced excavations in soft clays. This paper summarizes the formulation of numerical limit analyses that compute rigorous upper and lower bounds on the exact stability number and include anisotropic yielding, typical of $K_0$-consolidated clays and bending failure of the wall. Calculations for braced cuts bound the actual failure conditions within ±5%, and highlight limitations of existing basal stability equations. The analyses clarify how wall embedment and bending capacity improve the stability of well braced excavations. Careful selection of mobilized strengths at shear strains in the range 0.6–1.0% are necessary to match the predictions of anisotropic limit analyses with nonlinear finite-element predictions of failure for the embedded walls. Two example applications from recent projects in Boston highlight the practicality of the numerical limit analyses for modeling realistic soil profiles and lateral earth support systems, but also focus attention on the need for careful selection of undrained strength parameters. Credible estimates of stability have also been obtained in reanalyzing a series of case studies reported in literature using isotropic strength parameters derived from field vane or laboratory simple shear tests.

Stress-controlled undrained cyclic triaxial tests followed by strain-controlled monotonic compressive shear tests were carried out on normally consolidated and overconsolidated reconstituted Keuper Marl silt to investigate the strength and stiffness degradation characteristics of a low plasticity silt. Special attention was paid to the changes in undrained strength and deformation modulus after undrained cyclic loading. It was observed that cyclic degradation in stiffness for low plasticity silt is more marked than that of strength, and this tendency increases with increasing overconsolidation ratio. It was found that a previously proposed model for predicting postcyclic degradation in strength and stiffness of normally consolidated fine-grained soils could be applied to that of overconsolidated silt but not however to the postcyclic degradation in Young’s modulus. Thus, an attempt was made to correlate postcyclic degradation of overconsolidated silt to the equivalent cyclic shear strain instead of the normalized excess pore pressure. It was concluded that cyclic shear strain was a better parameter than cyclic-induced excess pore pressure for correlating the postcyclic stiffness degradation not only for normally consolidated but also for overconsolidated silt.

The effect of an initial static shear stress on the undrained cyclic loading resistance of saturated sand, as observed in laboratory testing, is often expressed in terms of a correction factor, $K_{\alpha }\text{.}$ Prior research has demonstrated that $K_{\alpha }$ depends on the state of the sand, as commonly represented by its relative density and confining stress conditions. This dependence of $K_{\alpha }$ on state is intuitively consistent with critical state concepts, but the implementation of this dependence in practice has been hindered by the absence of simple methods for estimating state and its effects without having to perform an extensive program of laboratory testing. In this paper, a simple index for representing state is derived from Bolton’s (1986) relative dilatancy index and shown to provide a reasonable and practical index for describing the variation of $K_{\alpha }$ with both relative density and confining stress.

The concept that plasticity index of soils can be defined as a range of water contents producing a 100-fold variation in undrained shear strength has been experimentally verified with the help of a large number of tests on soils of diverse nature. This has led to the redefinition of the plastic limit as the water content at which undrained shear strength is around 170 kN/m². Undrained shear strength of a soil at the liquid limit can be considered to be around 1.7 kN/m². Accordingly, both the liquid limit and the plastic limit have been determined in the present work by a single consistent method, i.e., the Swedish fall cone method. The undrained shear strength-water content relationship has been found to be log-linear for a wide range of water contents beginning from lower than the plastic limit to higher than the liquid limit. This resulted in the formulation of an expression for predicting undrained shear strength of a remolded soil at any water content based solely on its liquid limit and plastic limit.