降雨对泥石流源地土体活动的指数式放大效应

Exponential Amplification Effect of Rainfall on Slope Failures in Debris Flow Source Region

多数泥石流是从坡面活动开始的。坡面的不稳定土体活动,如崩塌、滑坡等,既是泥石流的物质来源,也决定着泥石流的形成方式和规模变化。四川汶川牛圈沟和北川魏家沟泥石流源地坡面人工降雨实验表明,坡面土体活动是间歇、涨落的随机过程,崩塌的时间间隔随着降雨强度的增大呈指数减小,每组实验中的崩塌总数目和雨强的关系如N=CN exp(kN IR);崩塌规模随着降雨强度的增大呈指数增大,每组实验中平均崩塌量与雨强的关系如M=CMexp(kM IR);坡面崩塌的总量可以表示为:V=NM=CNCM exp((kN+kM)IR);受土体颗粒粒径的影响,不同坡面崩塌量随雨强变化的参数不同,研究揭示了大规模泥石流的形成是由于源地土体活动强度随雨强的指数式增强。

Most debris flows are formed by slope failures, performing as landslides, collapses, and so on, which not only supply solid materials in debris flows, but also control the formation approach and magnitude variety. Field artificial rainfall experiments on slopes in debris flow source region in Niujuan Gully in Wenchuan County and Wei- jia Gully in Beichuan County show that the slope failure is actually a random, discontinues process with fluctuation in magnitude. The collapse interval exponentially decreases, while collapse magnitude exponentially increases with rainfall intensity. The relationship between collapse number, average collapse magnitude and the rainfall intensity can be described as N = CN exp（kN IR） and M = CMexp （kM IR） , thus the total collapse amount can be expressed as V = NM = CNCu exp （ （kN ＋ kM）IR）. The parameters in the equation is various due to the viriety of grain composition of the soils on slopes. This study shows the exponential amplification effect of rainfall on slope failure intensity, which can be regarded as the formation mechanism of giant debris flow in rain storms.