地震作用下堆积体边坡振动台模型试验及抛出现象分析

国道213线都江堰-汶川段普遍发育着堆积体边坡。在“5.12汶川地震”中,此类边坡更易发生滑坡灾害,并伴有独特的山石抛出现象。结合堆积体边坡实例进行振动台模型试验,研究堆积体边坡在多次地震作用下结构损伤累积并最终发生失稳的特征及边坡破坏模式。试验结果表明：堆积体边坡中上覆堆积体与下部基岩存在动力响应差异,边坡滑坡形式不同于静力失稳,表现为裂缝一旦出现便迅速扩展,边坡坡肩处部分小块体在水平和垂直向动力耦合作用下与原结构脱离抛出,这与汶川地震后边坡调研中发现的抛出现象一致。分析了模型边坡块体抛出现象与裂纹形成角度的关系,只有当裂纹角度和竖向加速度组合满足一定的触发条件时,才可能出现抛出现象。

Shaking table tests and throwing phenomenon of deposit slopes under earthquakes

The deposit slope is very typical along the highway from Dujiangyan to Wenchuan, China, where “5.12” Wenchuan Earthquake took place. The investigation of “5.12” Wenchuan Earthquake shows that most of the landslides occur in those slopes. In order to study the seismic failure mode of this kind of widely distributed slope, 1g shaking table model tests are carried out to study the mechanism of slope instability. According to the test results, difference responses between the deposit and the rock bed under dynamic conditions make the failure mode of the deposit slope different from those under the static conditions. A throwing phenomenon occurs at the upper part under the combination of horizontal and vertical shaking, which is widely reported in “5.12” Wenchuan Earthquake. A mathematical model is established to analyze the throwing phenomenon under earthquakes, and it is found that this phenomenon can happen only when the crack opening angle meets some conditions.