An Experimental Study on the Shear Characteristics of Typical Colluvial Soil with Gravel and the Stability of Slopes in Wenzhou, China

Slope disasters are an important area of concern in the prevention and mitigation of national land disasters. To study the stability of the slope in Wenzhou, China, the basic physical and mechanical properties of undisturbed soil in this area were obtained from laboratory experiments of typical colluvial soil. From experimental results, it was determined that the soil was low-liquid limit clay containing gravel. The shear characteristics of soil for different water content, gravel ratios, and burial depth were also obtained from large-scale indoor direct shear tests. The test results show that: (1) for colluvial soil without gravel, increasing water content increases cohesion, but decreases internal friction angle; (2) for colluvial soil containing gravel, the shear stress drops sharply when the shear displacement is close to approximately 15 mm; (3) for the same gravel ratio, the contribution of the gravel to the shear strength of the shear surface is not significant at lower vertical stresses, but increases at higher vertical stresses. A finite element strength reduction method has been used to numerically simulate the typical binary slope in Wenzhou. The simulation results show that the factor of safety of the binary slope is dependent on the strength of the overlying soil. The variations of the safety factor with water content and the gravel ratio are consistent with the variations of shear strength with the water content and the gravel ratio obtained from the tests. Simultaneously, the soil–rock interface strength needs to be addressed in the analysis of binary slopes.