Calculating the shear strength of a sliding asymmetric block under varying degrees of lateral constraint

The rock foundations of major gravity structures are seldom uniform, and often include large-amplitude roughness. When foundation topography is strongly asymmetric, sliding cannot occur without significant lateral dilation. An individual failing monolith is thus forced to interact with neighboring blocks, which resist its tendency to dilate. In this paper, we examine quantitatively the intuitive notion that increased lateral constraint leads to higher monolith effective friction angles. A simple asymmetric monolith is subjected to Lagrangian dynamic analysis under varying types of lateral confinement. Failure envelopes are compared for the laterally unconstrained, one-side constrained, and fully constrained cases, and it is shown that the combination of asymmetric foundation topography and two-sided lateral constraint yields a powerful strengthening mechanism. The frictional properties of the model dam foundation and monolith sides are then varied to investigate their influences on the overall monolith friction angle. It is shown that in some cases, a comparatively minor increase in frictional resistance along the monolith sides produces markedly improved sliding shear strength. This has important practical ramifications, since the interfacial shear properties of neighboring concrete monoliths are easier to control than the foundation petrology.