Finite-element analysis of softening effects in fissured, overconsolidated clays and mudstones
The softening process as observed in fissured, overconsolidated clays and mudstones is discussed in detail. Softening is classified into internal and external processes. The effect of softening is to decrease the shear strength of a material and its dilatant characteristics. This shear strength reduction is represented as a lowering of the failure envelope and a reduction in the degree of nonlinearity at low stress levels. There are some restrictions related to stress paths that affect the initiation of softening. The softening process may be formulated in terms of a time-dependent yield surface, and the finite-element method can be extended to analyze softening effects. A cut slope is analyzed as an example. The development with time of deformations is traced up to the collapse of the slope. This example contains the essentials to portray the role of the mechanism of softening. A distinction can be made between time-dependent deformation due to softening and those associated with conventional creep mechanisms. Key words: softening, time-dependent strength reduction, finite-element analysis.