Cyclic response of unsaturated weathered red mudstone under various conditions of initial static shear stress and moisture content

Abstract

Slope stability in weathered red mudstone (WRM) sediments during earthquakes is strongly dependent on the cyclic response of unsaturated WRM. In this paper, the cyclic simple shear tests on unsaturated WRM were conducted, and the influencing factors, including the moisture content (w), initial static shear stress (τs), cyclic stress amplitude (τcyc) and vertical stress (σv) were investigated in detail. The test results showed that the existence of τs affects the development patterns of shear stress–strain curves induced by increasing number of loading cycles (N). For specimens without τs, a closed hysteretic loop is formulated in each cycle, and no residual strain occurs. The hysteretic loop of WRM with τs is unclosed, and the residual strain accumulates with increasing N. The initial static shear stress usually exists within soil in slopping ground; thus, deformation accumulation is the main failure model under cyclic loading. The accumulated plastic shear strain was then presented in detail, and the test results indicated that the accumulated plastic shear strain at an identical cycle increases with increasing τs, τcyc and w, but decreases with increasing σv. Finally, the cyclic resistance corresponding to three identical accumulated shear strains (0.5%, 1.5%, and 2.0% in this study) was studied, and a unified cyclic stress ratio, USR, was proposed to build a united model of unsaturated WRM cyclic resistance, in which the effects of τs, σv, τcyc and w were considered uniformly.