The effects of lateral asymmetry on the shear strength of a sliding body.

摘要

The sliding motion of a frictional body over arbitrarily rough, asymmetric foundation topography always features an element of lateral displacement in addition to the prescribed forward displacement and expected vertical dilation. Over large distances, the lateral component of motion may be negligible compared with the amount of forward displacement experienced. Over small displacement distances, the lateral component may be the dominant feature of motion, and failure to consider it in strength analysis can lead to an incorrect understanding of sliding behavior. This is especially true when the sliding body under consideration is laterally bounded, as in the case of a gravity dam monolith.;This dissertation examines the strengthening consequences of lateral dilation in the context of gravity dam engineering. A simple but asymmetric foundation consisting of three discrete sliding planes is considered first. Lagrangian dynamic analysis is used to investigate the hydrostatically initiated downstream motion of a three-plane monolith over this surface, and to resolve the lateral dilation phenomenon into elementary sliding modes. The influences of shear force magnitude, foundation plane inclination, and foundation frictional resistance on sliding trajectory are probed, and it is demonstrated that the results of a laboratory experiment can be intrinsically tainted with testing machine bias.;The simple foundation and monolith are then subjected to simulated lateral constraint, and the relative strengths of unconstrained, one-side constrained, and two-side constrained monoliths (strongest) are compared. The relationship between a monolith's output effective (i.e. total or comprehensive) friction angle &phis;eff and its input foundation and side friction angles &phis; is investigated: It is shown that a rigidly constrained monolith exhibits good sliding resistance in the total absence of foundation shear strength, and that a modest side-friction increase can nearly double its shear strength.;The concluding section features an analysis of an in-service gravity structure with complex foundation topography. The practical usefulness of the Lagrangian model is confirmed by its ability to predict the trajectory and shear strength of a multiple-block wedge. The two-side constrained effective friction angle of the compound monolith is computed for different sets of input &phis;, and compared with the strengths of the individual constrained monoliths.