蒋家沟砾石土的特性及其对斜坡失稳的意义

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1 mm 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。

Characteristics of gravelly soil and their implications for slope instability in Jiangjiagou ravine

Jiangjiagou ravine is one of the most world-famous rainfall-induced debris flow or flow-like landslides gully in Southwest China. The surface layers of the slopes are covered by unsaturated weak-cohesion gravelly soil which can be classified as a porous non-plastic soil. Broadly graded gravelly soils have uniformity coefficients much greater than 20, and the grain size distribution curves are up concave or double peak, and they can be as internally unstable soils. The main clay mineral composition of fine fraction (<1 mm) of gravelly soil is chlorite and illite by X-ray diffraction analysis. The microstructure was investigated by environmental scanning electron microscopy; and a particular bonding was found. The bonding of the soil is easily broken by rainfall infiltration, which not only can decrease the soil cohesion, but also detach free particles from the bonding, the diameters of these particles were tens of microns. This is due to high dispersion of the clay part of gravelly soil. In addition, these free particles can be transported and will clog at pore throats during the process of self-filtration in soil. This process will decrease the permeability of gravelly soil, and be favorable to the formation of transient perched water zones in slopes during rainfall; thus can be as pre-failure of the slopes. The results indicate that the characteristics of gravelly soils and the particle detachment, transport and clogging play an important role in the stability of slopes.