中文摘要：

利用现场剪切试验、X射线粉晶衍射、电镜扫描及土水化学效应试验等手段探讨了降雨作用下欢喜坡冰水堆积体角砾土强度变化的微观机制。降雨对冰水堆积体角砾土的抗剪强度有着显著的影响,其饱和状态的黏聚力和内摩擦角比天然含水率情况分别降低64.3%和22.5%。降雨溶浸后,角砾土微观结构变得松散、黏聚力降低,其强度衰减的微观机制可概括为黏土矿物吸水膨胀,钙镁质胶结物溶解,离子交换吸附和角砾与水的微观作用,其主要表现为：黏土矿物吸水膨胀,粒间孔隙增大,其形态由絮凝状变为似层状或分散状;钙镁质胶结物溶解导致溶液中Ca^2＋、SO4^2-浓度出现明显增加;离子交换导致Na^＋浓度增大,黏土颗粒表面扩散层变厚,粒间引力减小;角砾与水的微观物理化学作用导致其粒间接触面粗糙度降低。

英文摘要：

The micro-mechanism of strength change of breccia soil in outwash deposit at Huanxipo under rainfall is examined using field shear test,X-ray powder diffraction,scanning electron microscope and soil-water chemical effect test. Rainfall has a significant effect on the shear strength of breccia soil in Huanxipo outwash deposit. When it is saturated,the cohesion and internal friction angle are 64. 3% and 22. 5% lower than those at natural water content. After soaked by the rain,the microstructure of soil become loose and its cohesion decreases. The micro-mechanism of strength attenuation can be summarized as the swelling of clay minerals,the dissolution of calciummagnesium cement,the ion＇s exchange and adsorption and the microscopic action of the breccia and water. Their mean performances are as follow. First,the clay minerals swell after absorbing water,causing its intergranular pores to increase and its form to turn from flocculent to layered or dispersed. Then,the dissolution of calcium-magnesium cement causes a significant increase in the concentration of calcium and magnesium ions in the solution. Then,ionexchange leads to an increase of sodium ion concentration,the thickening of diffusion layer in clay particle surface and the reduction of intergranular gravitational force. Lastly,the micro-physicochemical action of the breccia and water leads to a decrease in the interfacial contact surface roughness.