The distinct element analysis of soil masses

Abstract

The conventional Distinct Element Analysis of Cundall and Belytschko and their respective co-workers are prone to vibrations which must be damped out artificially if numerical problems are to be avoided. An alternative approach to this method is developed which eliminates such problems by allowing the elements to consolidate without gain in velocity. In the method employed here the contact forces, together with body forces due to gravity give rise to accelerations of the elements which in turn cause them to change position. Normally this change in position will produce an increase in the contact forces. Once these new contact forces have been calculated the elements are then returned to their original positions prior to the next iteration. The contact forces, therefore, increase during the analysis to counter the effects of gravity. Two methods using this new approach are described, for which computer programs have been written. The first program, SLICES, is designed to analyse slopes divided in to slices with a predetermined failure arc. During the analysis the program generates the stress profile acting on the failure arc and predicts the stability or otherwise of the slope. Program SLICES is compared with a traditional slice method under conditions of total and effective stress with cohesive and frictional soils. An analysis using a non-linear failure criterion is also carried out with program SLICES. The second program, CIRCLES, uses circles as the distinct element type and does not require a predetermined failure arc. It is shown that edge effects cause an incorrect stress regime to be set up that masks the failure process. However a sliding type failure is demonstrated where the edge effects do not mask the analysis. Submitted in accordance with the regulations for the degree of Ph. D. of the University of Durham. October 1989.