Failure propagation and mesh-dependency in coupled hydraulic-mechanical transient problems

We analyse the mechanism of failure propagation and the reasons for pathological mesh-dependency during excess pore pressure dissipation by studying a simple unloading problem numerically. We show that during the transient consolidation process, plastic deformations occur within a gradually propagating shear band of about 1-2 elements width. Once this band reaches the surface, no further stress redistribution is possible and the system reaches the ultimate state. Strain localization leads to pathological mesh dependency in the propagation speed of the shear band and thus also in the stand-up time of the system. The stand-up time depends on the finite element size, and tends to a non-zero value as the element size approaches zero.