Effects of Creep and Pore Pressure Diffusion on Shear Strength of Saturated Clay

This paper presents a numerical study into the competing influences of creep and pore pressure dissipation (diffusion) on the shear resistance of a stratum of saturated clay. The analyses comprised fully coupled mechanical-flow simulations using the user-defined viscoplastic constitutive model PM4SiltR in the finite difference program FLAC 8.1. Simulations were performed for a single soil layer under infinite slope loading conditions (analogous to simple shear loading). A target shear stress was imposed under undrained conditions, after which pore pressure diffusion was initiated while the target shear stress was maintained constant. Analysis results illustrate the competing influences of consolidation and creep on the pore pressures at different depths within the clay layer. Results are presented for cases that do and do not lead to undrained creep rupture. A framework that relates rate of consolidation characteristics and sustained static shear stress levels to the potential for creep failure is presented. The practical implications of the results are discussed.