初始含水率对冰川泥石流的起动影响分析

Influence of Initial Water Content on Glacial Debris Flow Triggering Process

通过开展不同初始含水率天然冰碛土的冰川泥石流起动试验,近似模拟不同前期降雨量下融水冲刷冰碛物形成泥石流的起动过程。结果表明:(1)研究区冰川泥石流起动类型为坍塌推移型;(2)初始含水率较低时渗流作用表现明显,渗流侵蚀将大量细颗粒运移,致使粒间孔隙增大至原孔隙率的2倍,土体骨架颗粒重新排列,颗粒间接触力降低,土体产生局部失稳变形,孔隙水压力呈"突降-突增-突降"趋势;(3)初始含水率较高时渗流与冲刷共同起主导作用,泥石流呈阵流爆发且与孔隙水压力峰值相对应;(4)含水率和孔隙水压力呈周期性变化,土体初始含水率与含水率达到峰值所需时间呈负相关关系;(5)基于试验现象及含水率和孔压的变化特征,将研究区泥石流起动过程划分为4个阶段,将其起动机理分为内渗流侵蚀、前缘骨架坍塌和径流冲刷起动。

Antecedent rainfall plays an important role in the triggering mechanism of debris flow.The glacial debris flow triggering experiments of different original soil water content were carried out to simulate the washed glacial drift triggering process under varieties of antecedent rainfall.The results showed that：（1）The evolution type of glacial debris flow in study area preliminarily could be defined as slope-slide model.（2）Seepage played a leading role at the low original soil moisture content.A large number of fine particles occurred,leading to the intergranular porosities increased to the original two times when grain-contact stress falling;then the rearrangement of the soil structure and enlargement of the pore-water pressure lead to the soil particles failure.It could be shown in the pore-water pressure as a＂fall-uprush-fall＂form.（3）Both Seepage and scour were key factors at higher original moisture content.The starting process of debris flow was intermittent,and the triggering moment that was the peak moment of pore-water pressure.（4）Both pore-water pressure and the volumetric soil water content showed periodical curves.The original soil water content was negatively associated with the debris flow starting time.（5）Based on the experiment phenomenon and the characteristics of curves,debris flow could be divided into four steps in this study.And the mechanism could be concluded to seepage erosion,soil front end framework and runoff scouring.