三峡大树场镇堆积层滑坡暴雨失稳机理研究

A study of the failure mechanism of rainfall-induced accumulation landslide in the Three Gorges Reservoir region

2014年9月1日,奉节大树场镇发生了大型崩塌堆积层滑坡,体积约37.8×104m3。基于大量的现场地质调查和室内分析,文章阐述了滑坡特殊的地质地貌及地质结构特征,分别从地质和环境因素两个方面进行了滑坡成因分析,采用非稳态非饱和渗流方法研究滑动失稳变形过程,并基于地貌学与工程地质力学理论推断滑坡形成演化过程。得出如下结论:(1)大树场镇滑坡为极端降雨诱发的近水平地层区崩塌堆积层滑坡,具有多次滑动特征;(2)特殊的地形地貌条件是滑坡形成的内因;极端强降雨是滑坡发生的直接诱发因素;(3)降雨前期,降雨主要通过入渗滑体增加其自重,入渗量大而渗流量小,对滑体稳定性影响较小;之后持续强降雨致使基岩顶面处的孔隙水压力不断增大,为滑体提供动态浮托力,加之滑体内部形成的渗流场导致稳定性大幅度降低;堆积体结构分布受控于基岩接触面形态,滑体不同区域达到饱和状态时间存在明显差异性是多次滑动变形破坏的理论依据;(4)短时极端降雨触发堆积层局部饱和岩土体由蠕滑逐步形成小规模滑坡碎屑流;持续极端降雨导致基岩顶面富集大量地下水,使堆积层岩土体呈饱和-过饱和状态,形成大规模滑坡碎屑流。

On September 1,2014,a large-scale collapse accumulation landslide occurred near the Dashu village,Fengjie County with about 37. 8 × 10^4m^3 in volume. On the basis of field investigation and lab analysis,the special geologic environment and characteristics of the Dashu landslide are studied in detail. The origin of the the Dashu landslide is analyzed from the two aspects： geologic origin and the environment origin.The deformation and sliding process is examined with the theory of transient unsaturated seepage. The formation mechanism and evolution process of the landslide are proposed tentatively. The results show that（ 1）the Dashu landslide is extreme rainfall-induced accumulation landslide in nearly horizontal stratum area,and has the characteristics of multiple sliding;（ 2） the particular geological structure is the inner factor of landslide formation; the extreme intense and large rainfall is the main and direct triggering factor of landslide formation;（ 3） during the early stage of rainfall,rainfall mainly infiltrates the slide mass to increase its weightwith a large amount of infiltration and small amount of seepage flow,which has less influence on the stability of the slide mass. Then continuous heavy rain led to the increasing pore water pressure of bedrock surface,which provides the dynamic buoyancy for the slide mass. Combined with the seepage field effect,the slide mass stability is significantly decreased. Slide mass structure distribution is controlled by the form of bed rock contact surface,and the saturated state time exists obvious differences in different areas of the sliding mass,which is the theory basis of multiple sliding failure of slide mass.（ 4） sort-term extreme rainfall made the local accumulation rock mass saturated,and triggered it creep gradually to form small landslide debris flow; and continuous extreme rainfall led to enrichment of groundwater above the bedrock top surface, made the accumulation of the saturated and oversaturated condition,and formed a large-scale landslide debris flow.