汶川地震中国道G213左侧某典型高山河谷场地地震滑坡响应分析

ANALYSIS OF LANDSLIDE RESPONSES OF A TYPICAL HIGH HILL-RIVER VALLEY FIELD NEAR NATIONAL ROAD G213 DURING WENCHUAN EARTHQUAKE

以国道G213左侧一处包含河谷地形的高陡边坡为原型,采用新型离散元计算方法——基于连续模型的离散元方法(CDEM),对高烈度地震作用下高陡边坡上的堆积体滑坡由变形累计到破坏滑动的全过程进行模拟,并结合振动台试验结果,对该高陡边坡上堆积体的地震滑坡响应进行研究。研究结果表明,在地震力和重力作用下,堆积体顶部先出现应力集中,造成堆积体沿基岩–堆积体结构面后缘产生变形,进而造成该处出现拉伸、剪切破坏点,之后随着地震动的持续,基岩–堆积体结构面上的剪切破坏点逐渐向堆积体中前部的锁固段扩展,同时伴随着堆积体表面拉伸破坏点的增加,最终造成锁固段发生渐进性破坏,堆积体从剪出口滑出形成滑坡。滑塌发生的时间与地震动峰值加速度到达的时间同步或稍微有所滞后。在高陡边坡地形中,以输入地震波为基准,不论是坡面还是坡体内,不同位置的峰值加速度沿坡高均有所放大,表现为竖向峰值加速度的放大效应>水平峰值加速度的放大效应,坡面峰值加速度的放大效应>坡体内峰值加速度的放大效应。在河谷地形中,以输入波为基准,不论是河床还是河岸两侧的斜坡,不同位置的峰值加速度沿高程均具有不同程度的放大;河谷对加速度放大效应的影响具有一定范围,且在该范围内水平加速度的放大效应>竖向加速度的放大效应,与坡面处加速度的放大效应刚好相反;加速度的放大效应具有一定的方向性,且该方向性与河岸两侧斜坡的坡度有关;加速度放大效应在河谷底部的分布具有不均匀性,距离河岸越近,加速度放大效应越强烈。

A high steep hill with river valley near initial deformation to sliding of the slope during ground shaking is simulated by a new discrete element method--continuum-based discrete element method（CDEM）. Combining with shaking table test results, seismic landslide responses of accumulation body of the high steep slope are analyzed. The analytical results are as follows. The stress concentration phenomenon appears at the top of the accumulation body firstly and then some tension failure points and shear failure points appear there, which expands toward the toe of the accumulationbody from the top of that along the accumulation body-bed rock structural plane. At the same time, the number of tension failure points gradually increases. At last, the toe of the accumulation body-bed rock structural plane breaks; and then the accumulation body shears out from the toe, which results in the landslide. The starting time of landslide and the arrival time of peak ground acceleration（PGA） are synchronous or the former lags behind the latter slightly. In the high steep area, based on the input seismic wave, regardless of on the slope or inside the slope, peak acceleration is amplified as elevation increases. Generally speaking, amplification of the vertical peak acceleration is larger than that of horizontal peak acceleration; and the amplification of peak acceleration on a slope is larger than that inside the slope. In the river valley topography, based on the input seismic wave, regardless of the river valley or the backsides, peak ground acceleration is also amplified as elevation increases. There are some influence scopes of river valley on acceleration amplification effect. In this scope, the amplification of the horizontal peak ground acceleration is larger than that of the vertical peak ground acceleration. The amplifications of accelerations have obvious directivity of topographic effects, which are related to the gradient of bank sides. Distribution of acceleration amplification effect is nonuniform in river valley; and the smaller the distance to bank sides is, the stronger the acceleration amplification effect is.