A formulation for modeling soil-structure interaction has been presented. In conjunction with the formulation, a computer code was written to implement it. Several problems were analyzed to demonstrate the accuracy of the code. The program called SEQCON utilizes an eight-node isoparametric quadrilateral. An interface and tar element are also available. Four material models are used. They are the linear elastic, the hyperbolic, the trucker-Prager, and the cap model. Several construction sequence steps were modeled. They include in situ, dewatering, excavation, deposition (embankment) and tie-backs. The code itself is modular in design and quite flexible. It is easy to implement and to modify. / M.S.

A computer program based on the finite element procedure was modified to analyze the multipass effect of rubber-tired vehicles on soil compaction. The wheel-soil interaction was modeled as an axisymmetric problem by approximating the elliptical wheelsoil contact area with an equivalent circular area. A hyperbolic stress-strain relationship was used to model the nonlinear material characteristics of the soil. The boundary load conditions were based on contact area and contact pressure data for a standard tire. The finite element program developed was verified by conducting a linear elastic analysis of a circular flexible footing problem and comparing the results with closed form solution. The results of the finite element analysis agreed well with the closed form solution. The effects of soil type, wheel-soil contact area, and multiple wheel loading on soil compaction were analyzed. The results of the analyses provided information on soil displacement, stress distribution, and volumetric strain. Residual volumetric strain contours, developed after each loading and unloading cycle (simulating the passage of a wheel), showed zones of maximum compaction and the propagation of compaction zones as a function of the number of wheel loadings. A major portion (80% - 90%) of the total residual volumetric strain was found to occur during the first wheel pass. The rate of increase in volumetric strain dropped noticeably as the number of passes increased. As expected, results of the analysis show that for a given vehicle weight, the use of large tires minimizes the degree of compaction. / Master of Science