柿树沟泥石流为暴雨型泥石流,研究该物源土体前期的含水率及密实程度对于分析该类型泥石流的形成具有重要意义。在降雨过程中物源土体逐渐饱和且细颗粒也随之发生运移,造成了土体密度的改变及强度特征的影响。以柿树沟泥石流物源土体为研究对象,采用室内大型直剪试验,研究其在不同饱和度和干密度条件下的强度特性,分别得到饱和度、干密度与抗剪强度指标c和φ的关系,与强度包线的关系,与剪应力及位移的关系。结果表明:土样c值与饱和度成反比,与干密度成正比关系,且饱和前期变化较为明显;剪应力-位移曲线随着饱和度的增加峰值逐渐明显;前期充分降雨情况下,土体逐渐饱和且抗剪强度迅速下降,在径流作用下表层松散堆积物易被裹挟带走,形成泥石流。通过试验的研究,可以获取此类粒径组合下的泥石流物源体的强度指标变化特性,对该类泥石流的形成机制或预测预报的研究具有一定的参考和指导意义。

Debris flows of Shishu gully are induced by rainstorm, and it is important to study the impacts of moisture content and compaction rate of source-region soil on the formation of debris flow at early stage. During rainfall, source-region soil is gradually saturated and fine grain moves, which leads to the changes of soil mechanical properties such as density and strength. In this paper, we carry out direct shear test on source-region soil of debris flow in Shishu gully by using large-scale apparatus to explore strength behavior in the presence of different degrees of saturation and dry densities. We obtain the relationships of saturation and dry density vs. shear strength index c (cohesion) and φ (inner friction angle), as well as relationships of saturation and dry density vs. strength envelope, shear stress, and horizontal displacement, respectively. The results show that: 1) relationship between c and saturation shows tendency of inverse proportion, whereas c is in proportion with dry density , especially at early stage of saturation; 2) shear stress vs. horizontal displacement curve’s peak becomes obvious as the degree of saturation increases; 3) in the presence of adequate rainfall at early stage, source-region soil gradually becomes saturated and sudden drop of shear strength occurs; then, loose deposits at the surface layer are easy to be taken away by water flow, which causes the formation of debris flow. Through the experiment, we obtain the variation behavior of strength index for source-region soil of such grain size distribution.The results offer reference for the research of formation mechanism and the forecast of such debris flow.