关键词: 砾石土, 斜坡失稳机理, 泥石流, 微观结构

Abstract:

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.

Key words: gravelly soil, mechanism of slope instability, debris flow, microstructure