汶川地震次生泥石流形成模式与机理

Formation mode and mechanism fordebris flow induced by Wenchuan earthquake

以汶川地震灾区的典型的代表性泥石流案例为基础,分析了汶川地震次生泥石流的形成地形地貌、降水和土源条件特征,概括分析了汶川地震泥石流形成的5种模式,即:(1)沟床启动型;(2)坡面崩滑转化型;(3)震裂表土侵蚀启动型;(4)滑坡表面土体液化型和(5)松散坡积物冲切沟启动型。分析了这些形成模式的启动机理。地震次生泥石流的形成机理包括土力类和水力类。泥石流的形成需要一定的细颗粒含量,尤其是粘土颗粒含量;此外低密度干燥度较高的土体在降雨作用下易湿陷,体积收缩,从而有利于土体孔隙水压力的升高,而有利土体强度的降低,导致泥石流的启动。所以地震灾区的泥石流集中分布于干旱河谷松散固体物质大量存在且以花岗岩风化壳和碎屑岩及其变质岩为主的地区,降雨量特征与国内外众多泥石流的降雨特征可以比较,其模式多样。

This paper is based on combination study of the ＂5.12＂ Wenchuan earthquake-induced typical debris flow events. In the paper the debris flow landscape and landform, the precipitation and the earth condition were studied firstly. After that the Wenchuan earthquake debris flow-triggering models were revealed. These models inelude （1） valley triggering; （2）slope collapse and landslide triggering; （3）loose soil eroded by stream and rains; （4） landslide surface liquefied; （5） gully eroded. And the debris flow-triggering mechanism was explained at last. The debris flows of quake - stricken area distribute in the arid valley which, abounds in weathered crust granite, elastic rock and metamorphic rock, and the Precipitation nodes