A study was undertaken to investigate the bearing capacity of rectangular footings on geogrid‐reinforced sand by performing laboratory model tests as well as finite‐element analyses. The effects of the depth to the first layer of reinforcement, vertical spacing of reinforcement layers, number of reinforcement layers, and the size of reinforcement sheet on the bearing capacity were investigated. Both the experimental and analytical studies indicated that there was an optimum reinfprcement embedment depth at which the bearing capacity was the highest when single‐layer reinforcement was used. Also, there appeared to be an optimum reinforcement spacing for multi‐layer reinforced sand. The bearing capacity of reinforced sand was also found to increase with reinforcement layer number and reinforcement size when the reinforcement was placed within a certain effective zone. In addition, the analysis indicated that increasing reinforcement stiffness beyond a certain value would not bring about further increase in the bearing capacity.

A procedure for nonlinear system identification of soils using strong‐motion records obtained in a downhole seismograph array is presented. This study uses, in conducting the identification, the extended Kalman filter, which is a sequential parameter estimation scheme. The Bouc‐Wen model is used in characterizing the nonlinear backbone curve of soils, and a generalized Masing's rule is implemented to model stress reversals. The stress‐reversal history obtained from earthquake data may be ambiguous. To avoid using a faulty stress‐reversal history, only a fraction of the earthquake data is used. The ground is modeled as a three‐degree‐of‐freedom hysteretic structure. Identification is first carried out based on soil hysteresis loops, using a weighted global iteration scheme. These results are then incorporated into the identification of the ground. The parameters identified yield shear wave velocities that are in good agreement with those from cross‐hole measurements. Similar agreement is also seen between the calculated accelerations and the actual records.

The present paper provides an analysis of self‐boring pressuremeter tests in sand in terms of the state parameter. The method developed herein can be used to determine the in‐situ sand state from the results of the self‐boring pressuremeter test. Unlike the conventional drained pressuremeter analyses that almost exclusively use an elastic‐perfectly plastic model, the new analysis is based on a strain‐hardening (or softening) plasticity model in which the angles of friction and dilation are assumed to be a function of the state parameter. The numerical results presented suggest that there is a unique linear correlation between the loading slope of pressuremeter curves and the initial state parameter of the soil. It is therefore possible to deduce the state parameter of the sand from the measured pressuremeter loading slope. The relevance of this new analysis has been confirmed by the results of the pressuremeter test carried out in large calibration chambers.

Experimental laboratory‐scale studies were conducted on the effect of the use of various mineral and polymer drilling slurries on the perimeter load transfer in drilled shafts in saturated sand. Parallel measurements were also made of the rheological properties of the slurries studied in order to develop ranges of slurry control properties consistent with predictable load transfer. Polymer slurries, mixed in medium to high doses, were found to be as effective as the more familiar mineral slurries in the development of load transfer. No slurry, however, produced the magnitude of perimeter load transfer that was developed on model drilled shafts constructed by inserting casing ahead of the drill in medium‐dense, saturated sand and withdrawing the casing as the simulated concrete was placed.

Following a brief review of the inaccuracies that may result from the use of a popular model for evaluating the dynamic soil pressures and associated forces induced by ground shaking in a rigid wall retaining an elastic stratum, the sources of the inaccuracies are identified and a modification is proposed which, while retaining the attractiveness of the original model, defines correctly the action of the system. In the proposed modification, the soil stratum is modeled by a series of elastically supported, semiinfinite horizontal bars with distributed mass rather than by massless springs. The concepts involved are introduced by reference to a fixed‐based wall retaining a homogeneous elastic stratum, and are then applied to the analysis of more complex soil‐wall systems. Both harmonic and transient excitations are considered, and comprehensive numerical solutions are presented that elucidate the actions of the systems examined, and the effects and relative importance of the numerous parameters involved.

Formally probabilistic methods for the analysis of slope stability have had relatively little impact on practice. Many engineers are not familiar with probabilistic concepts, and it has been difficult to incorporate concepts of reliability into practice. Also, there is confusion over what reliability and probability of failure mean. The most effective applications of probabilistic methods are those involving relative probabilities of failure or illuminating the effects of uncertainties in the parameters. Attempts to determine the absolute probability of failure are much less successful. The paper describes how probabilistic descriptions of soil parameters can be derived from field and laboratory data and applied in stability analysis. The first‐order, second‐moment approach is explored and applied to the design of embankment dams. The example illustrates the relative contributions of uncertainties about different parameters to the reliability of the embankment. Reliability analysis is especially useful in establishing design values of factors of safety representing consistent risks for different types of failure.

Based on a synthesis of published laboratory data, two types of cyclic threshold shear strain are examined and their approximate magnitudes identified for different types of soils. They are the linear cyclic threshold shear strain, ${\gamma }_{\mathrm{tl}}$ and the volumetric cyclic threshold shear strain, ${\gamma }_{\mathrm{tv}}$, with ${\gamma }_{\mathrm{tv}}>{\gamma }_{\mathrm{tl}}$. These strains represent boundaries between fundamentally different categories of cyclic soil behavior. For cyclic strains below ${\gamma }_{\mathrm{tl}}$, soil behaves essentially as a linearly elastic material. Between ${\gamma }_{\mathrm{tl}}$ and ${\gamma }_{\mathrm{tv}}$, soil becomes markedly nonlinear but remains largely elastic because permanent changes of its microstructure still do not occur or are negligible. Above ${\gamma }_{\mathrm{tv}}$, soil becomes increasingly nonlinear and inelastic, with significant permanent microstructural changes taking place under cyclic loading. That is, ${\gamma }_{\mathrm{tv}}$, = the threshold separating cyclic strains that cause or do not cause significant permanent changes of soil microstructure. In practical terms, these microstructural changes are manifested in residual cyclic pore‐water pressures in fully saturated soils and permanent volume change in dry or partially saturated soils. Both ${\gamma }_{\mathrm{tl}}$ and ${\gamma }_{\mathrm{tv}}$ depend on the type of soil and are correlated to soils plasticity index (PI). Based on these correlations with PI, a new rational categorization of cyclic shear strains with respect to their magnitude and type of soil is proposed. This categorization enables selection of appropriate type of soil dynamics analysis for given soil and anticipated level of cyclic shear strain.

A t‐bar penetration test for soft clay that can be performed with existing cone penetration test (CPT) equipment is described. The results of the test can be directly related to the undrained shear strength of the clay via a plasticity solution, thus eliminating some of the uncertainty involved in the interpretation of conventional penetration tests in soft clay. Results from a field trial of the device are shown to compare favorably with the results of other in‐situ and laboratory strength tests.

Dynamic centrifuge modeling was used to study the behavior of two mildly sloping ground models subjected to earthquake loading and liquefaction. The first model consisted of a uniform layer of saturated sand, and the second consisted of a layer of sand overlain by a relatively impermeable layer of nonplastic silt; both model slopes were constructed at an angle of 2.6°. Time histories of acceleration, excess pore‐water pressure, and displacement are presented with photographs to illustrate the mechanisms of failure. In both tests approximately 0.8 m of prototype lateral displacement was measured at the surface. In the uniform sand model this lateral displacement was distributed throughout much of the layer; however, in the layered model displacement was concentrated along the interface between soil layers. The concentration of displacement is consistent with a reduction in the sliding resistance between the silt and the sand layers due to the redistribution of voids at the interface. This possibility of redistribution of voids indicates that care must be taken when using undrained strengths in the postliquefaction analysis of layered slopes.