This thesis studies the influence of the residual shear strength of soils on the stability of landslides.

The effect of rate of shear on the residual strength of soils is studied in a modified Bromhead ring shear apparatus. It is found that the loss of soil about the perimeter of the apparatus may introduce pore pressures at fast shearing rates, and a method of deriving the maximum shearing rate is proposed.

A silty clay is tested over a wide range of shearing rates and normal stresses. With increased rate of shearing, the soil shows a reduction in strength at slow rates, and an increase at fast rates. These results are compared with studies of rate effects for other soils and rocks, and a mechanism to explain the observed phenomena is proposed.

The behaviour of four landslides is reviewed in the light of the residual strength study, and it is concluded that rate effects are one of the important factors in determining the future stability of a landslide.