Effect of shear rate on the residual shear strength of pre-sheared clays

This paper presents the result of an experimental study on the shear behaviour of a pre-sheared clayey soil. The effect of shear rate on the residual strength of pre-sheared clays was investigated in a ring shear apparatus. A pre-sheared surface was initially developed at a slow rate of 0.1 mm/min. Fast shear rates were then applied to the pre-sheared specimens to investigate the impact of the shear rates on the results. The laboratory results show that there is an immediate tendency for the residual strength to increase with increasing shear rate. Following this, the fast residual strength continues to increase with further displacement, reaching the peak value of fast residual strength (i.e. positive rate effect). Finally, the fast residual strength drops with increasing displacement to a value less than slow residual strength (i.e. negative rate effect). Overall, the relationship between the residual strength and the fast shear rates indicates a positive and negative rate effect based on the shear rates and the shear displacement.