高混凝土面板堆石坝地震损伤机理研究

Seismic damage mechanism of high concrete face rockfill dams

以紫坪铺面板堆石坝为例,基于堆石料的黏弹性模型和地震残余应变模型计算分析了高混凝土面板堆石坝的地震响应,并结合震害调查结果分析了高混凝土面板堆石坝的地震损伤机理。研究表明,输入地震加速度在坝顶附近和坝坡表面显著放大,呈现出显著的鞭梢效应,导致坝顶和下游坝坡上部堆石体松动滚落。地震导致大坝堆石体产生显著剪缩,坝体断面整体向内收缩,刚性混凝土面板与垫层料之间脱空,脱空后面板与垫层料之间的摩擦力大幅减小甚至消失,面板在自重和地震惯性力联合作用下向下滑动,致使面板水平施工缝发生错台,面板表面产生裂缝。地震还导致岸坡附近左右坝段堆石体向河谷中央位移,致使岸坡附近面板垂直接缝发生拉伸破坏,河床中部垂直接缝及附近混凝土面板发生挤压破坏。数值计算和震害调查结果均表明,高混凝土面板堆石坝的地震损伤现象主要与其堆石体地震残余变过大,以及堆石体与防渗系统之间变形不协调密切相关,故强震区修建高面板坝应尽可能提高堆石体压实密度,以减小坝体的地震残余变形。

Based on the case study of Zipingpu concrete face rockfill dam（CFRD）, the visco-elastic model for rockfill materials and the model for their residual strain are employed to investigate the seismic responses of high CFRDs, and the mechanism of their damage behaviors is studied combined with the field observations. The numerical results show that the input accelerations are considerably amplified within the top zone and the surface of the dam, and the so called whipping effect does exist in high CFRDs. Therefore, the rockfill materials near the crest and the downstream slope shake to be loose and some particles even fall along the slope. Strong shaking also results in evident shear contraction of rockfill materials and leads to considerable settlement of the dam. As a result of the contraction of the dam shell, the third stage concrete slabs separate from the cushion layer and the frictional forces between them disappear, and the shear failure occurs in the horizontal construction joints and tensile crack occurs on the surface of the cantilever slabs under the combined action of gravity and seismic inertia forces. During the earthquake, the rockfill materials move towards the center of the canyon, resulting in strong compressive stresses, and thus, the compressive failure within the slabs is near the center. In contrast, the vertical joints near the bank is generally suffered by tensile failure. Both the numerical results and the field observations show that the damage behaviors of high CFRDs subjected to earthquakes are closely related to the excessive residual deformation of rockfill materials and large difference in rigidities of concrete slabs and rockfill materials. Therefore, for building a high CFRD in earthquake regions, the compaction criteria for rockfill materials should be properly enhanced to reduce its possible earthquake-induced deformation.