Slope failure mechanism of decomposed granite soil considering the variation of shear resistance under low pressure

为探讨崩解花岗岩土边坡的破坏机理，进行了离心机模型试验。边坡破坏类型多为浅层滑移型。此外，针对分解花岗岩土的剪切特性，进行了低围压和中压下的直剪试验和三轴压缩试验。利用两种压力下的三轴压缩试验得到的强度参数，用有限元方法计算了分解花岗岩土边坡的安全系数。主要研究结果如下：1)对于腐解花岗岩土，低围压和中压下的抗剪强度常数(c，Phi)有一定的差异。尤其是低围压下的表观凝聚力要小于中压下的表观凝聚力。浸水引起的抗剪强度下降程度大于低围压地区大于中压地区。2)在低围压下，表观粘聚力在小剪位移处达到峰值，之后保持不变。在低围压下，残余状态下的表观凝聚力下降与最大表观凝聚力的比值较大。3)非饱和风化花岗岩土边坡破坏试验和降雨作用下风化花岗岩土边坡破坏试验均为浅滑滑动型。4)低围压下的抗剪强度取值是进行边坡稳定性分析的重要依据。采用有限元方法，通过考虑低压力下抗剪强度变化的边坡稳定性分析，可以解释边坡的破坏机理。

In order to investigate the slope failure mechanism of decomposed granite soil, centrifuge model tests were conducted. Shallow sliding type of slope failures were observed. Moreover, in order to the shear characteristics of decomposed granite soil, direct shear tests and triaxial compression tests were carried out under low confining pressure and moderate pressure. Using strength parameters obtained from triaxial compression tests under both pressures, the safety factors of decomposed granite soil slopes were calculated by finite element method. The results summarized as follows :1)For decomposed granite soil, some differences in the constants of shear strength(c, phi)were obtained between low confining pressure and moderate pressure. Particularly, the apparent cohesion under low confining pressure is less than that under moderate pressure. The degree of decrease in shear strength due to soaking is greater than in the region of low confining pressures than at moderate pressures. 2)Under low confining pressure, apparent cohesion peaks at small shear displacement and stays constant after that. The ratio of decrease in apparent cohesion at residual state to the maximum apparent cohesion is large under low confining pressure. 3)Sballow sliding type were observed from the slope failure tests of unsaturated decomposed granite soil and the slope failure tests of decomposed granite soil due to rainfall. 4)The values of shear strength under low confining pressure are important and necessary for the analysis of the slope stability. Using finite element method, the slope failure mechanism can be explained by slope stability analysis considering the variation of shear resistance under low pressure.