成都龙门山区地震崩积砾石土特征及泥石流启动阈值研究

The earthquake triggered debris flows in Longmenshan Mountains of Chengdu which caused huge casualties and property damages, present a great threat to the downstream villages and the recovery.The debris flow were massive in total volume, group-occurring and latency, according to these character, the monitoring and warning system will be an economic and effective process. The core of the monitoring and warning system is the threshold value of debris flow initiation. This study is going to disclose the character of wide-graded gravel soil from debirs flow source region and propose its initiation threshold value such as rainfall intensity, pore water pressure and water content through laboratory and field experiments. Firstly, we will make out the distribution character of wide-graded gravel soil from debirs flow source region through the distribution character and field investigation. And the physical, mechanical character of gravel soil from debirs flow source region will be disclose through the laboratory experiments and theoretical analysis.Then, the threshold value of earthquake triggered gravel soil failure and debris flow initiation, including rainfall intensity, pore water pressure and water content will be proposed through field experiments, which could support the debris flow initiation research and monitor-warning system in the research area.

成都龙门山区地震次生泥石流灾害具有规模超大性、群发性和潜伏性等特点，近年来已造成严重人员和财产损失，严重威胁灾区恢复重建。面对日益严重的泥石流灾害，监测预警将是及时有效而经济合理的防灾手段，而泥石流监测预警系统的核心就是泥石流启动的特征阈值。本研究将通过室内外试验相结合的方法对泥石流源区地震崩积砾石土的特征及其启动泥石流时的特征阈值进行探索。研究中先通过遥感解译和野外调查分析地震次生泥石流源区崩积砾石土的分布规律；然后根据室内外实验和理论分析研究崩积砾石土体的物理及力学特征；再通过野外泥石流启动原型试验研究崩积砾石土土体破坏启动泥石流时的降雨量、土体孔隙水压力和土体含水量特征阈值，为研究区泥石流灾害的监测预警提供依据。

“5.12”汶川地震灾区泥石流灾害具有规模超大性、群发性和潜伏性等特点。针对这些特点，监测预警将是及时有效而经济合理的防灾手段，而泥石流监测预警系统的核心就是泥石流启动的特征阈值。本研究通过野外调查、历史数据统计分析、理论分析和室内外实验研究了成都龙门山区地震崩积砾石土特征及其破坏启动泥石流时的特征阈值，取得了以下成果：. (1)成都龙门山区降雨丰富、坡度陡峻再加上汶川地震诱发形成的大量松散固体物质，完全满足泥石流形成要求。成都龙门山区现有松散地震崩积物29993.65×104m3，其中彭州和都江堰两市地震崩积物分布较为集中，占整个研究区总量的81.7%，这与“5.12”汶川地震后研究区内泥石流灾害实际分布情况相符合。. (2)作为成都龙门山区近期泥石流主要物源的地震崩积砾石土都为宽级配土，且砾石含量较高，达35.7%-77.3%，大多数沟道的黏粒含量低于2.0%。研究区代表性泥石流沟内崩积砾石土的平均干密度1.39-1.52g/cm3，天然质量含水量变化于3.81%-9.49%。灰岩类崩积砾石土天然含水量大于砂岩类的崩积砾石土天然含水量，灰岩类崩积砾石土的渗透性低，砂岩类崩积砾石土的渗透性高。在相同的含水量条件下，崩积砾石土的内聚力低于残坡积物，内摩擦角高于残坡积物；在相同含水量条件下，随着密度的增加，崩积砾石土的内聚力 在增加，而内摩擦角 变化不大；在相同密度条件下，随着含水量的增加，崩积砾石土的内聚力 值存在一个最优含水量下的最大值，内摩擦角 随含水量的增加有减小趋势。.(3)地震崩积砾石土破坏启动泥石流的特征阈值.1)在近似相同初始含水量和降雨强度的条件下，土体大规模启动时的含水量随土体密度的增加出现增加的趋势，启动的时间随土体密度增加也出现增加的趋势；在近似相同初始含水量和密度的条件下，土体大规模启动时的含水量随降雨强度增加没有表现出明显的增加趋势，而土体大规模启动的时间随降雨强度的增加出现减小的趋势。.2)研究区地震崩积砾石土土体破坏启动产流的降雨量阈值为10.0mm/h，孔隙水压力阈值为平均孔压的120%，土体含水量阈值为饱和含水量的80.0%。.