The residual strength of clay is taken into consideration in the stability analysis of landslids, but the present technology is in such a state that the method of measuring residual strength is not established as yet. The residual strength varies with the type of measuring apparatus used such as ring shear apparatus or reversal direct shear apparatus and also it varies with clay sample condition such as disturbed or undisturbed. The present research is focussed on the condition of clay sample and its relation with residual strength. As a common practice the residual strength of clay is measured with the sample in disturbed condition and with the basic conception that it is not influenced by the stress history. In this research residual strengths of the same clay in both disturbed and undisturbed conditions are measured and obviously the results are different. Thus it is to be suggested that the residual strength should be measured with the clay sample in undisturbed condition.
