Comparison of the shear strength of unsaturated sandy soils at optimal and residual moisture contents

The shear strength of soil is a key input parameter required for the satisfactory geotechnical design of any structure. The existence of most residual soils in unsaturated conditions highlights the importance of studying the shear strength of unsaturated soils. In this study, a modified triaxial apparatus was used to examine the mechanical behavior of 5 types of silica sands with mean grain sizes varying from 0.15 to 1.5 mm. The experimental test results of soil shear strength determination were compared with the shear strength estimated through analytical methods. To study the mechanical behavior of test soils at optimal and residual moisture contents, the test samples were initially prepared at the optimal moisture content. To study the effect of the initial moisture content on the mechanical behavior of test soils at the residual moisture content, the test samples were initially prepared at the optimal and residual moisture contents. Residual moisture content samples exhibited higher shear strength compared to optimal moisture content samples. Furthermore, the residual moisture content samples prepared at the optimal moisture content exhibited stronger mechanical behavior compared to the sample prepared at the residual moisture content. The analytical methods employed in this study were not able to accurately predict the shear strength of test soils at residual moisture content.