Research On Strength Characteristics Of Unsaturated Basalt Residual Soil And Its Slope Stability

By the local tropical rain climate,basalt residual soil of GuiZhou Province is always in unsaturated state,whose strength is very different from saturated soil;In the rainy season,the loss of matrix suction leads the decreases of its strength,which can easily leads to geological disaster such as slope instability and collapse and brings a serious threat to the local life and property safety.Therefore,it is of significant to research on strength characteristic of unsaturated basalt residual soil and its slope stability.On the basis of existing research,a lot of tests on the brown basalt residual soil were conducted.Main work and achievement are as follows:(1)The basic physical and mechanical properties of the basalt residual soil were obtained through laboratory tests.(2)The soil water characteristic curve(SWCC)of basalt residual soil was obtained by the filter paper and the axis translation technique.Then,the influence of dry density on the SWCC was analyzed,and the VG model was determined as the optimal model.(3)The influence of matrix suction on the shear strength was studied by the shear test of controlling the matrix suction within the range of 300 kPa,and the applicability of the shear stress formula of the double stress variable was verified.(4)The influence of water content on shear strength was studied by the shear test of controlling water content,and obtained the apparent cohesion and friction angle along with the change of water content;The shear strength characteristics of unsaturated basalt in a large matrix suction range(about 3000kPa)was analyzed by using the SWCC;The difference between the two tests methods was studied by comparing the tests with controlling the matrix suction.(5)To probe the variation law of slope safety coefficient with water content,Abaqus was used to establish the slope finite element model based on the selected slope,and the stability analysis of slope with different water content was carried out by strength reduction method;Combined with the SWCC,the influence of matrix suction on slope stability was studied,and it was concluded that the decrease of matrix suction caused by the increase on water content was one of the most important causes of slope instability.