圆形河谷地形效应振动台模型试验研究

Shaking table tests on topographic effects of circular-arc valleys

河谷作为一种局部不规则地形,会改变局部场地范围内的地震动特性,通常称之为地形效应,这一现象已经被大量地震动观测和震害记录所证实。目前关于河谷地形效应的研究多集中于解析解和数值方法,但缺乏试验数据的支撑。建立了考虑河谷地形效应的自由场振动台模型试验方法,开展了多工况自由场河谷地形效应的振动台模型试验研究。试验设计了3组宽深比分别为8︰1,4︰1,3︰1的圆弧形河谷地形,并以平整场地条件下的自由场试验作为参照,对比分析了河谷场地的地形效应,并探明了不同地形条件对自由场河谷地形效应的影响规律。试验结果表明:河谷地形效应会引起局部非平整场地范围内地表加速度响应的普遍放大,且以谷顶位置处的地震动放大效应最为显著,谷内加速度响应则表现为从谷底到谷顶逐渐增大的分布趋势;随着入射波频率的增加,河谷地形引起的地表加速度放大效应更加显著;而随着河谷地形深宽比的增加,地震动放大效应将逐渐增强。研究成果可为河谷地形条件下基础设施结构的抗震安全性分析提供科学依据。

As a typical locally irregular topography,the valley can change the seismic properties within the local site,which is usually called the topographic effects.This phenomenon has been confirmed by numerous ground shaking observations and earthquake damage records.However,the current knowledge on the site effects of the valley is focused on analytical or numerical methods,lacking the experimental data from physical models.In this study,a free-field shaking table model test method considering the valley effects is established,and a series of shaking table tests on the topographic effects of valleys are carried out.Three sets of circular-arc valley topographies with depth-to-width ratios of 1/8,1/4 and 1/3 are designed,and the free-field tests under the flat field are used as a reference to compare the topographic effects of the valley site,and the effects of different topographic conditions on the valley effects are investigated.The results show that the valley effects cause the amplification of the ground acceleration response at the local site,and the amplification effects are most significant at the valley top,while the acceleration response within the valley gradually increases from the valley bottom to the valley top.The ground acceleration amplification effects caused by the valley topography are more significant with the increase in the incident frequency.The amplification effects of the valley topography gradually increase with the increase of depth-to-width ratio.The research results can provide a scientific basis for the seismic safety analysis of structures around valleys.