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地震反应分析中的输入界面是一种规定的假想基岩面,其选取具有很大的不确定性,对确定地震动参数的影响很大。本文以北京地区存在剪切波速较高的卵石硬夹层场地为研究对象,探讨实际工程场地中能否将硬夹层选作地震动输入界面的问题。利用一维等效线性化波动方法,对390个含有剪切波速高于500m/s的卵石层场地模型进行地震反应分析计算,讨论卵石层的上覆土层、下伏土层以及卵石层自身特性对地震反应分析结果的影响。计算结果显示,厚度5m左右、剪切波速小于600m/s的卵石层作为地震动输入界面是否合理,主要取决于上覆土层和下伏土层,而卵石层厚度和剪切波速的影响很小。对于一般性工程,当上覆土层厚度大于15m,下伏土层厚度在10m以内时,选取硬夹层顶面与选取钻探揭示的基岩或剪切波速不小于500m/s的土体顶面为输入界面,计算结果差别不大;当上覆土层厚度达到60m,下伏土层的变化对计算结果影响很小。研究表明,在钻探没有揭示出基岩或坚硬土体时,埋深大于60m的硬夹层可以选为地震动输入界面,这一结论对实际的地震安全性评价工作具有一定参考价值。
The input interface in seismic response analysis is a kind of presumed hypothetical bedrock surface. Its selection has a great deal of uncertainty and has a great influence on the determination of ground motion parameters. In this paper, the existing pebble hard interlayer in Beijing area with high shear wave velocity is the research object, and the problem of whether hard interlayer can be selected as input interface of ground motion in actual engineering site is discussed. Using the one-dimensional equivalent linearized wave method, the seismic response analysis and calculation of 390 pebble bed site models with shear wave velocities higher than 500 m / s are carried out to discuss the pebble bed overburden, underlying soil and pebble layer’s own characteristics Impact on seismic response analysis results. The calculation results show that the thickness of 5m and shear wave velocity of less than 600m / s pebble layer as a ground motion input interface is reasonable, mainly depends on the overlying soil and underlying soil, and pebble layer thickness and shear wave velocity little effect . For general engineering, when the thickness of the overburden is more than 15m and the thickness of the underlying soil is within 10m, the top surface of the hardclay and the bedrock or the top of the soils whose shear wave velocity is not less than 500m / s When the thickness of overlying soil reaches 60m, the change of underlying soil has little effect on the calculation results. The results show that the hard interlayer with the buried depth greater than 60 m can be selected as the input interface of ground motion when the rock or hard soil is not revealed by drilling. This conclusion is of certain reference value for the actual earthquake safety assessment.