Influence Of Matrix Suction On Loess Slope Stability

In view of such disasters as landslides and debris flow, loess slope collapse, roadbed subsidence, underground tunnels instability and deep foundation pit slope spalling in loess areas caused by heavy rainfall, earthquake and other natural disasters pose severe threats to human life and property. Therefore, the study on the stability of loess slope is of realistic significance. For the Lanzhou loess with large thickness, the underground water level is extremely deep, loess is usually in unsaturated state, the matrix suction of unsaturated loess soil makes great contribution to the shear strength. However, matrix suction is influenced by various factors such as water content, it is difficult to measure efficiently and accurately in laboratory. At the same time, typical soil-water characteristic curves shows that matrix suction are influenced by soil water content significantly.For unsaturated loess in Lanzhou region, it was configured to unsaturated homogeneous remolded loess in different water contents, regular consolidation undrained triaxial tests were conducted, the stress-strain curve and corresponding shear strength parameters cohesion and angle of internal friction under different water contents were obtained, then data was graphed, it shows as water content increases, cohesion first increases then decreases and the the variation is big, the friction angle first increases then decreases and the the variation is small, curve extreme value point near the water content of10%. Then, two homogeneous loess slope were established, which their slope angle are45°nd66°. Using the strength reduction finite element method, parameters obtained from text were input to the loess slope stability calculation model in turn after reduction for simulation and analysis using ABAQUS finite element analysis under soil self-weight based on the Mohr-Coulomb theory. According to the curves of field variables FV1(reduction coefficient) and X direction displacement of U1, neglecting the influence of other conditions, the safety factor Ks of loess slope stability corresponding to for different water content was calculated, the resulting curve fitting for the two function, can get fitting coefficients were first working0.85and second working0.71. Known from the relation curve of water content and the loess slope safety coefficient, with the increasing of water content, safety coefficient increases firstly and then decreases, the maximum of water content occurs at about10%, the safety coefficient decreased rapidly when the water content exceeded the optimum water content. The reason of the conclusion is the matrix suction of unsaturated loess decreasing gradually with the increase of water content, so that the soil shear strength decreases, and thus safety coefficient decreases. The isoline chart of slope displacement can be obtained by simulation, the shape of sliding surface and the displacement range can be clearly visible.Therefore, based on the results of trials and ABAQUS finite element simulated analysis, this study drawn some revelent conclusions, which has certain economic and practical significance for conducting higher level researches on losess properties, engineering design and construction in urban in Lanzhou unsaturated loess area in the future. What’s more, this study has certain indicative value to the prediction of the security and stability of loess slope, and the support of loess slope as well.