湖南临湘贺畈沟灾害性泥石流成因分析和启示

摘要

In order to find out the genesis of the extraordinary debris flow disaster which took place in Hefangou gully of Hunan Province, where is a wet area of low seismic intensity, on June 10th in 2011, the drought grade of Hefangou Basin before the dis-aster was determined and the effect of lasting drought on the physical and mechanical characters of the granite residual soil was analyzed on the basis of field investigation and laboratory test. Besides, the rainfall quantity and time required to saturate the granite residual soil was calculated. Then the genesis of the debris flow was obtained: the vertical layered characteristic of the granite residual soil determined that the soil can easily start from the surface with high content of fine particles;early long dura-tion drought cracked the soil structure and speeded up the soil weathering along the part with high content of fine particles near ground surface, which increased the permeability of the soil;later heavy rainfall of short duration caused the rainwater to infiltrate along the cracks on the soil surface with fine soil particles moving, enriched and then formed the impermeable layer of soil, the strength of the soil decreased;with the continued heavy rainfall, the pore water pressure above the impermeable layer in the up-per soil soared to some extent, the soil failed and was liquefied to form the debris flow.%2011年6月10日，属湿润、低地震烈度区的湖南临湘贺畈沟暴发了历史罕见的特大泥石流灾害。为探明此次泥石流灾害的成因，在现场勘查工作的基础上，结合室内试验，划分了泥石流发生前贺畈沟流域的干旱等级，分析了长历时干旱对沟内花岗岩残积土物理力学性质的影响，计算了花岗岩残积土饱和所需的降雨量和时间，得出了此次泥石流灾害的成因：源区花岗岩残积土的垂直分层特征，决定了土体极易从细颗粒含量高的表层起动；前期长历时干旱导致土体表层沿细颗粒含量多的部位开裂，土体局部渗透性加强；在后期短历时强降雨作用下，雨水沿干裂缝等表层通道下渗，土体中的细颗粒发生运移、富集并形成局部隔水层，土体强度降低；随着降雨的进行，隔水层上部土体中孔隙水压力升高，土体破坏并液化形成泥石流。相关结论对于开展花岗岩残积土起动形成泥石流过程特征及机理研究具有启示意义。