A simplified cost‐effective analytical‐numerical procedure is developed for the nonlinear hysteretic seismic analysis of three‐dimensional (3‐D) nonhomogeneous, one‐zone earth dams. The procedure can be applied efficiently to problems of the nonlinear dynamic response of soil and/or soil‐structure systems. The procedure is based on a Galerkin formulation of the 3‐D equations of motion in which the solution is expanded using 3‐D eigenmodes of the linearized 3‐D problem. The linear mode shapes are obtained using low‐strain elastic moduli and a variational energy approach utilizing both Hamilton's principle and the Rayleigh‐Ritz method. The nonlinear approach is based on a modal discretization of the spatial domain in which 3‐D linear modes are coupled due to material nonlinearity. The dynamic constitutive behavior of the dam materials is modeled using the concept of multiyield surface incremental plasticity in which a purely kinematic hardening rule is adopted. Spatial integrations are performed using a numerical scheme in which Gaussian quadrature is adopted. The time integration of the resulting semidiscrete matrix equation is performed using the Newmark method. Finally, in the analysis, all three directional input ground motions are considered simultaneously; nonlinear dynamic transient solutions, including permanent deformations, can be obtained at modest computational expenses.

The procedure outlined in the companion paper is applied to compute the nonlinear response of an earth dam to a 3‐D input strong motion with recorded maximum acceleration of 1.2 g (in the upstream‐downstream direction). Special features of the nonlinear seismic response due to the highly strong shaking are explored. Because of the modal expansion concept utilized in the procedure, insight is gained into the contribution of different modes to the response of the dam at different locations. Finally, comprehensive comparisons are made with results obtained through a more elaborate nonlinear, 3‐D, finite element analysis of the dam. The comparison indicates that the proposed simplified analysis method can be used to reliably estimate the entire time history of all response quantities and the resulting permanent deformations of earth dams subject to earthquakes. In addition, it is found that the computed results agree reasonably well with those of the finite element analysis; further, the “modal” nonlinear procedure is found to be reasonably accurate and extremely efficient computationally.

A large‐scale group of nine steel‐pipe piles in a closely‐spaced arrangement was subjected to two‐way, cyclic, lateral loading with water above the ground surface. The test was conducted in stiff, overconsolidated clay at a site in Houston, Texas. All of the piles in the group were extensively instrumented to allow the results to be compared with those from other piles in the group and from the testing of an isolated, single pile. The results emphasize the highly nonlinear nature of the pile‐soil‐pile interaction. A substantial reduction in ultimate soil resistance was measured in the group piles relative to that of a similarly loaded single pile for both the first cycle and for 100 cycles of load.

The response of soil loaded in a pressuremeter test is inherently time‐dependent; even for an “undrained” test in a clay, some consolidation will occur. The pressuremeter expansion will also be affected by creep of the soil skeleton, and thus both the results and the derived parameters will be influenced by the testing technique adopted. To examine the influence of time, the problem has been examined both experimentally and numerically. Pressuremeter tests have been simulated in the laboratory by expanding cylindrical cavities using different incremental pressure techniques in three types of clay prepared with known stress history, and the results compared with finite‐element predictions. The finite‐element program is based on critical‐state soil mechanics and includes both consolidation and deviatoric creep. This has given a new insight into the behavior of clays during pressuremeter tests. The results indicate that any simple standardization of pressuremeter test technique should be approached with caution.

Experiments determining the dynamic stiffness of footings attached to or embedded in the model half‐space were conducted. The footings, both circular and rectangular, were forced into vertical vibration, and the dynamic stiffnesses were measured by use of a mechanical impedance measurement technique. The results of the experiments are given by graphs for dimensionless frequencies smaller than eight. The measured results may be approximated with adequate accuracy by second‐degree polynomials in terms of dimensionless frequency. The coefficients of the polynomials for each footing are presented. The polynomial expressions for an elastic case estimated from the results of the experiments are also presented. The model half‐space was made of RTV (room temperature vulcanizing) silicone rubber. The material of the model half‐space has small hysteretic damping; the Poisson's ratio of the material is close to 0.5. The footing‐model half‐space interface can be regarded as bonded.

A technique is developed for compiling liquefaction hazard maps by mapping a parameter termed liquefaction severity index (LSI). LSI, a measure of ground failure displacement, is based on the displacement of lateral spreads on gently‐sloping late Holocene fluvial deposits such as floodplains and deltas. By selecting a specific geologic environment, LSI is normalized with respect to site conditions. LSIs are evaluated for several earthquakes in the western United States, and an equation is developed between LSI, earthquake magnitude, and distance from the seismic energy source. This equation and a model of seismic energy sources is used with a published seismic risk algorithm to compile probabilistic LSI maps for southern California. The maps show contours of LSI with 90% probability of nonexceedance in periods of 10, 50, and 250 years. LSI maps are useful for determining the relative liquefaction hazard and provide an index of possible maximum ground displacement.