高土石坝-地基动力相互作用的影响研究

我国土石坝建设高度已迈入300 m级,其体积和质量巨大,坝-基交界覆盖区域(建基面)沿顺河向长可超千米,且筑坝材料具有非线性特性,地震时的坝-基动力相互作用问题越发受到工程界的关注,亟待开展系统研究。本文以我国已建和拟建的若干代表性高土石坝工程为背景,采用波动分析方法考虑坝-基动力相互作用,系统地讨论了地基截取范围的影响,并通过与传统振动分析方法对比,研究了坝-基动力相互作用对大坝地震反应的影响。结果表明:高土石坝的地震反应计算采用波动分析方法更符合实际;在考虑坝-基动力相互作用时,建议地基截取范围取坝-基交界面顺河向长度的0.3～0.5倍(面板坝时约1.0H～1.5H,心墙坝时约1.2H～1.8H,H表示坝高);与振动分析方法相比,波动分析方法获得的坝体加速度极值降幅约为10%～40%,动位移极值降幅约为10%～50%,面板动应力极值降幅:拉应力约为20%～40%,压应力约为15%～30%。可见,坝-基动力相互作用的影响是显著的,振动分析方法不能反映地震对大坝作用的实际情况,高估了大坝的地震反应,从而低估大坝的极限抗震能力。

Influence of the dynamic interaction between high rockfill dam and foundation

The height of several rockfill dams in China has exceeded 300m with tremendous volume and weight, and the length of dam-foundation interface is over thousand meters along the river. In addition, since rockfill materials have nonlinear property, the influence of dam-foundation dynamic interaction during earthquake causes attention more and more in the engineering,and is necessary to study systematically. According to the several representative high rockfill dams constructed and awaiting construction in China, the wave analysis method is adopted to consider dam-foundation dynamic interaction and study the influence of intercepted range of foundation on the dam dynamic response. Through contrasting the results of vibration analysis and wave analysis, the influence of the dynamic interaction between high rockfill dam and foundation is discussed. The results indicate that the dam dynamic response calculated by wave analysis method conforms to reality better than the vibration analysis method,and suggest that the intercepted range of foundation is equal to 0.3 to 0.5 times of the length of dam-foundation interface along the river. In other words, the range is about 1.0 to 1.5 times of the height of dam for the concrete-faced rockfill dams, and the range is about 1.2 to 1.8 times of the height of dam for the core-wall rockfill dams. Compare with the results of vibration analysis method, the acceleration extreme values of dam calculated by wave analysis method decrease about 10%~40%, the dynamic displacement extreme values of dam decrease about 10%~50%, and the dynamic stress extreme values of concrete face slab decrease about 20%~40% (tensile) and 15%~30% (compressive), respectively. Therefore, the influence of dam-foundation dynamic interaction is significant,and the vibration analysis method will overestimate the dynamic response of high rockfill dam to underestimate the seismic capability.