Effect of interface element type on soil-structure interaction

Abstract

A comprehensive literature survey and review of all interface elements so far developed and implemented within their limited scope of applications have been carried out in this study. From the literature survey, three major types of interface elements such as, Goodman (1968) Type, Katona (1983) Type and Desai (1984) Type have been selected for. further study depending on their successful application to physical problems. These three most important interface elements are judged in an existing nonlinear incremental-itrative generalized elasto-plastic Finite Element Method (FEM) program. '* The parameters controlling the main features of each interface elements have been , , identified. These parameters are examined.critically in a typical problem setting of directshear box simulation. In order t~ investigate the evolution of different internal variables like deformation, strain or stresses, various types of figures have been drawn. Each case of analysis resulted in outputs of: (a) deformed mesh; (b) force-deformation and stress-strain relationship inside the interface; (c) shear strain contours; and (d) displacement fields. As most of the figures were drawn at different load steps in order to trace the progress of the variables, it was rather easy to identify the trouble spots for a particular type of interface. The contrast between an analysis in direct-shear box without an interface element .1" and with an interface element is very clear. Goodman (1968) type of interface performed well in direct shear simulation. The performance of this interface depends on the relative stiffness of the interface compared to the surrounding soil. Its behavior also depends on the thickness of the interface and load eccentricity from the interface. It shows distinct si,gnof mesh penetration at higher shear deformation. Katona (1983) type interface .element is the simplest interface in terms of number of parameters required. It does not have any penetration or separation problem. The performance in slip mode is ideal although not realistic. The performance of Desai (1984) type interface element seems to be the most realistic although it showed tendency of mesh penetration. It also showed better convergence ii properties. Reduction in the thickness of the element improves the performance of the Desai . ,{ type element. Finally, it can be concluded that among the three interfaces studied in this research, Katona and Desai type of interface element are much better in accuracy and although, practically Goodman type of interface is easy to formulate and to implement.