The existing literature on the rate effects on residual strength is reviewed. Clearwater clay-shale, present in the foundation of Syncrude Tailings Dyke situated in northern Alberta, is tested under different rates, in both ring shear apparatus and the direct shear box. The clay-shale, which has a Plasticity Index of 107%, a Liquid Limit of 135%, natural water content of 23% and clay content of 49% shows an improved residual shear resistance at higher rates. It is found that the residual strength is increased by 3.4-3.5%, for a tenfold increase in the strain rate. The tested range of displacement rates is 0.185 mm/day to 7.0 mm/day. Judging from the existing literature on such rate effects, a broad correlation between the plasticity of clay and rate effects is obtained.

By extension of the plasticity theory, a constitutive relationship is developed to model the strain rate-dependence of residual strength. It can be easily incorporated into existing finite element plasticity codes. The model is coded in the program $\rm PISA\sp{TM}$ (Chan and Morgenstern, 1992) and calibrated using an illustrative example.

A simulation of construction movements at Cell 23 of Syncrude Tailings Dyke has been done. Cell 23 of the tailings dyke has been identified as a problem area where more than 38 cm of horizontal movement has been observed at some locations over a period of 11 years. Clearwater clay-shale, present beneath portions of the dyke, is found previously sheared, due to glacial drag forces of the overlying till. The use of the rate-dependent model, for the shear zone, was found to provide a satisfactory basis for simulation of the movement pattern. The results of the deformation analysis provide the anticipated field velocities and show how they deteriorate with time to a reasonable accuracy.