Strength of different clayey soils and its prediction

The shear strength of unsaturated soils is a fundamental property in the unsaturated soil mechanics. A systematical study of the strength behavior of the silty clay, Madrid clay and Nanyang weakly expansive soils in the literatures is carried out in this paper. The strength characteristics can be divided into three types: the peak value of shear strength appears in a certain suction range, the strength is almost not affected by suction after reaching a certain suction value, and its strength increases with the increasing suction during shearing. In addition, the method based on capillary action and water film absorption is used to fitting the soil water characteristic curve (SWCC) in the full suction range. This method can separate the capillary water characteristic curve from the absorption water characteristic curve. The capillary water plays a key role in the strength component caused by imposed suction in the unsaturated soil. The strength equation for the unsaturated soils can be modified by the capillary component of degree of saturation. Finally, the modified shear strength criterion is used to predict the strength of soils of the three different types in a wide range of suction. The predicted results can capture well the measured test data in the transition zone, but further studies are necessary to predict the shear strength for different soil types in a high suction range.