震后沟道泥石流启动条件——松散堆积体雨中失稳的水力学机制分析

5.12地震导致大规模的松散崩滑物质堆积于沟道，极大的增加了震后降雨型沟道泥石流爆发的概率。然而，灾后特殊的物源条件和成灾环境改变了传统沟道泥石流的形成机制，给震后沟道泥石流的防治工作带来了巨大的困难。为此，以水文学为基础，在构建松散堆积体潜水位变化水文学模型的前提下，借助水力学理论，分析了沟道堆积体内水力随潜水位变化的规律和特征，研究作用在单元条块堆积体上静水压力和动水压力的计算方法。在合理分段沟道松散堆积体的前提下，基于无限边坡理论完成了对各段堆积体下滑力、基底抗滑力及剩余下滑力的表达构建。结合算例解析了震后降雨条件下堆积体失稳的力学机制。分析表明，震后沟道松散堆积体失稳启动并泥石流化是流域降雨作用下堆积体内潜水位不断抬升、水力环境不断劣化的结果。流域大、沟道窄、堆积深、导水系数小、沟床缓的堆积体因较高的潜水位更易在降雨中失稳，且失稳模式因条块间剩余下滑力差异而分为整体推移启动及解体牵引启动两类。

Analysis of condition of startup of gully debris flow after earthquake-The hydraulic mechanism of instability of loose deposits in rainfall

Because large quantities of loose deposits were accumulated in gully after "5.12" Earthquake,the occurrence probability of gully debris flow is enhanced greatly in rainfall.However,due to the special conditions of provenance and disaster environment,the traditional theory cannot be used to expound the mechanism of gully debris flow and prevent the disaster effectively as ever after the event.Here,based on hydrology,the hydrological model of ground water table in loose deposits is established first.Then by aid of hydraulic theory,the change of hydraulic characteristics and the variation of hydraulic power with the rising of groundwater level are analyzed.Furthermore,the calculation formulas of hydrodynamic and hydrostatic pressure are also proposed.Finally,by applying infinite slope theory in calculation of sliding force,anti-sliding force and residual sliding force acting on each segment,the failure mechanism of accumulation body is illustrated clearly with an example.The result indicates the failure of loose deposits in rainfall is the result of increase of the hydraulic power with the rising of groundwater level.Those deposits which have small coefficient,gentle slope,narrow-deep gully and large basin would be easy to fail because of its high hydraulic pressure generating in rainstorm,and the failure modes can be divided into two types according to residual sliding force as pushing failure and hauling failure.