秦巴山区宁陕县城坡面型泥石流的形成机理

近年来,在异常强降雨下,秦巴地区大型滑坡、泥石流灾害频繁发生,尤其是高陡斜坡上罕见的坡面型泥石流不仅突发性强,而且成灾面积大,造成的经济损失十分惨重。本文以2003年8月29日发生于秦岭造山带腹地宁陕县城区的坡面型泥石流为例,通过野外地质调查和室内试验测试,分析了暴雨作用下宁陕城区高陡斜坡带坡面型泥石流的发育特征及其形成机理。作者认为,除了持续集中的特大暴雨和斜坡陡峻等因素外,斜坡表层残坡积物的物质组成尤其是残坡积土的粘粒含量和粘土矿物成分是坡面型泥石流大面积同时发生的重要控制性因素。通过不同含水状态下的粘性土抗剪强度试验结果统计分析,剖析了暴雨坡面型泥石流的形成过程,探讨了斜坡浅表层残坡积物快速流动变形的临界状态,从而为地质灾害预测预警提供了科学依据。

Research on the formation mechanism of debris flow on slope around Ningshan County in the Hinterland of the Qinling Orogen

The special geological environment of Qinling region leads to complicated characteristics of topography and geological structure,and controls the unloading and weathering near the surface of the crust,which control the formation of surface geohazards.In recent years,large scale landslides and debris flows occurred frequently due to the effects of the coupling of endogenic and exogenic geological processes.Among the all kinds of geohazards,the debris flow on slopes usually brings with much economical loss for its high paroxysmal occurrence and large scale of damage.Taking an example of the debris flow on slope around Ningshan County in the middle of the Qinling Orogen on August 29,2003,based on field investigation and lab experiments,this paper analyzes the development characteristics and formation mechanism of a debris flow on slope.It is considered that,besides the factors such as continuous rainfall and dip slope,etc.the composition of the material on the slope,especially the content of clay-size fraction and the composition of clay minerals,is the dominant factor which led to simultaneous occurrence of debris flow on slope in a large scale.Base on statistic analysis of the shear strength test results under different water contents,the process of rainfall induced debris flow on slope,as well as the critical state of the slope material fast deformation,are derived,which provide an important evidence for geohazard control.