Direct shear tests on three types of expansive soils at different water contents

Abstract

Expansive soils are widely distributed in the foundation soil of water conveyance canals in Northern Xinjiang, and their strength characteristics are very obviously influenced by the water content. The increase of water content in the canal foundation soil caused by seepage and other reasons is very likely to cause canal slope collapse. The shear strength characteristics of three expansive canal foundation soils were studied using undrained direct shear tests, and the effect of soil body water content variations on the safety factor of simple homogeneous canal slopes was analyzed. The results show that with the increase in water content, the peak shear stress of the soil body decreases significantly. The peak shear stress of the green soil is low at 18 kPa at the water content of 30% and the normal stress of 300 kPa, with a decrease of more than 93%; the friction angles of the three soil bodies decrease significantly with the increase of water content, and there exists a critical water content value, and the internal friction angle decreases to almost 0 when the soil body water content is greater than this value. The critical water contents of the yellow, red, and green soil bodies were 21.9%, 22.8%, and 18.6%, respectively. The soil body cohesion decreases linearly with the increase of water content, and the decreased amplitudes of all three soil bodies were more than 80% after the water content increased from 10% to 30%. The safety coefficient of the canal slope decreases significantly with the increase of water content, and when the water content is greater than 22% at a volumetric weight of 19 kN m-3 and a slope height of 5 m, the safety coefficient of the green soil canal slope decreases to less than 1.