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云南蒋家沟是世界上著名的由降雨导致泥石流、浅层滑坡频发的沟谷之一。组成蒋家沟斜坡表层的砾石土具有孔隙度高、级配宽、不均匀系数大等特点,级配曲线为上凹型或双峰型,为内在不稳定性土。X射线衍射分析表明,粒径小于1mm的细粒部分主要由绿泥石和伊利石等黏土矿物及次生石英组成,黏土矿物会影响砾石土的物理力学性质。在环境电镜扫描中观测了砾石土的微观结构,发现一种特殊的“桥式”胶结结构,并在遇水条件下发生断裂,不仅降低了微弱黏聚力,而且土颗粒容易分离成粒径为数十微米的散微粒。这与砾石土中黏性部分具有高分散性有关。此外这些散微粒在自滤过程中会能发生运移,并在孔喉等处积聚而堵塞孔隙,会降低砾石土的渗透性以及有利于斜坡中暂态上层滞水的积聚。
Yunnan Jiangjiagou is one of the most famous valleys in the world where rains and shallow landslides are caused by rainfall. The gravelly soil that forms the surface layer of the Jiangjiagou slope has the characteristics of high porosity, wide grading and large nonuniformity coefficient. The grading curve is concave or bimodal with inner instability. X-ray diffraction analysis shows that the fraction of fine particles with a diameter of less than 1 mm mainly consists of clay minerals such as chlorite and illite and secondary quartz, and the clay minerals will affect the physico-mechanical properties of the gravel soil. The microstructure of gravel soil was observed in an environmental scanning electron microscope and a special “bridge” cemented structure was found and fractured under water conditions not only to reduce weak cohesion but also to separate the soil particles into Particle size of tens of microns scattered particles. This is related to the high dispersibility of the sticky part of the gravel soil. In addition, these scattered particles can migrate during the process of self-filtration and accumulate in pores and throats to plug the pores, thereby reducing the permeability of gravel soil and facilitating the accumulation of stagnant water in the transient upper layer of the slope.