全风化混合花岗岩边坡降雨冲刷试验研究

Experimental study on rainfall erosion of completely decomposed migmatitic granite soil slope

为了探究全风化混合花岗岩的冲刷破坏演化规律,设计了坡面降雨冲刷试验。借助高密度电法和面波测试方法,选取云南临沧南部山区混合花岗岩边坡进行现场冲刷试验,并构建了全风化混合花岗岩边坡入渗侵蚀量化评估方法,对全风化混合花岗岩边坡降雨冲刷破坏特征进行了分析。结果表明:1)边坡受雨水冲刷的影响深度分为3层,即0~0.5 m表层、0.5~1.6 m中层和1.6 m以下深层;2)侵蚀过程分为3个阶段,即①雨水溅蚀、入渗阶段,雨水溅蚀,坡面岩土体结构发生初始破坏,平均电阻率升高,剪切波速降低;②下层潜蚀入渗饱和阶段,雨水入渗饱和,岩土体结构进一步破坏呈松散砂状,坡面径流量较小,表层岩土体保持较好的完整性;③细沟贯通冲蚀破坏阶段,表土层平均电阻率迅速升高,剪切波速大幅度降低,坡面径流量增加,细沟贯通延伸至坡脚并出现大规模片蚀。以剪切波速变化率和电阻率变化率为基础建立的全风化混合花岗岩边坡入渗侵蚀量化评估方法,可为全风化混合花岗岩工程边坡冲刷治理提供可靠的技术支撑。

In order to explore the elolution law of erosion failure of completely decomposed migmatitic granite,a rainfall erosion test was designed.A slope in south mountain area of Yunnan Lincang was selected to conduct on-site test of completely decomposed migmatitic granite slopes using high-density electrical and surface wave testing methods.The seepage erosion quantitative estimation method for completely decomposed migmatitic granite slopes was built to analyze rainfall erosion failure features of these slopes.The results show as following.1)The influence depth of the slope affected by rainfall erosion can be divided into three layers,0~0.5 m surface depth,0.5~1.6 m middle depth and 1.6 m deep depth.2)The erosion process was divided into three stages:①spattered rainwater infiltration stage,rainwater spatters,soil mass structure on slope surface begins breakage,average resistivity increases rapidly,shear wave velocity decreases rapidly;②submergence infiltration saturation stage,rainwater seep into slope and soil is saturated,soil mass structure is destructed to be like loose sand,slope surface runoff decreases,lower soil mass can hold its integrity;③rill through erosion failure stage,the average resistivity of the topsoil increases rapidly,the shear wave velocity decreases significantly,the slope runoff increases,and the rill extends to the foot of the slope with large-scale erosion.The infiltration erosion model of the completely decomposed migmatitic granite slope is established on basis of the shear wave velocity change rate and resistivity change rate,which can supply a solid technical foundation for the erosion control of completely decomposed migmatitic granite engineering slopes.