SHEARING CHARACTERISTIC OF SLIDING ZONE SOIL FROM RING SHEAR TESTS FOR LARGE SCALE MUDSTONE LANDSLIDES IN HUANGSHUI RIVER BASIN

Large mudstone landslides are one of the main geological disasters in Huangshui River Basin in Qinghai Province. In the paper, the sliding zones of two typical large mudstone landslides in the area are taken as examples. Ring shear tests with different shear rates are conducted on the soils. The dynamic shear characteristics of the soils with different moisture contents in the sliding zones are revealed. The test results show that the soils in the sliding zones are expansive mudstone, and have obvious strain softening characteristics. The stress rapidly and significantly dropped from the peak stress to the residual stress (stress drop rang focused on 30%~40%). The shear strength has a negative relation with shear rate and moisture content. The response of the residual stress to these factors is less than the peak stress. The greater the moisture content (shear rate), the greater the change extent of shear stress and shear strength. The findings provide reasonable evidence for mechanism analysis and stability evaluation of landslide deformation in Huangshui River Basin.