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土体剪切波速是工程场地地震效应评价的重要参数之一。基于苏州城区的大量剪切波速实测资料和工程地质特征,探讨了第四纪深厚沉积层剪切波速结构空间变化特征,给出了不同工程地质分区的土层剪切波速随深度变化的经验公式;基于不同深度范围内土层平均剪切波速间存在的显著相关性,建立了基于浅层剪切波速外推深层剪切波速的逐步外推法,验证结果表明:(1)苏州城区等效剪切波速νs20和νs30的空间展布具有显著的分区特征,覆盖层厚度d>80 m的Ⅲ类和Ⅳ类场地的等效剪切波速分界值νs30可以取为170 m/s。(2)平原区土层剪切波速随深度的变化呈幂律函数关系;丘陵区细化为三个小的区域后,各分区内土层剪切波速随深度的变化呈二次多项式关系。(3)逐步外推法具有很好的适用性,但当外推深度处的土层剪切波速存在剧烈变化时,剪切波速的逐步外推法失效。(4)基于剪切波速逐步外推法,可给出剪切波速不小于500 m/s和700 m/s的任意假想基岩面埋深Hrock及相应的微震动场地卓越周期Tg,发现Tg值和Hrock值的空间展布基本一致;选取剪切波速不小于700 m/s的土层顶面为地震基岩面时,各工程地质分区的Tg值和Hrock值空间展布的差异性显著增大。
Soil shear wave velocity is one of the important parameters for evaluating the seismic effect of engineering site. Based on the data of massive shear wave velocity and the engineering geological features in Suzhou urban area, the spatial variation characteristics of the shear wave velocity structure in deep sedimentary layers of Quaternary are discussed. The empirical formula of shear wave velocity with depth in different engineering geological zoning is given Based on the significant correlation between the average shear wave velocity of soil layers in different depths, a stepwise extrapolation method based on the extrapolation of shear wave velocity at shallow shear wave velocity was established. The results show that: (1) Suzhou urban area is equivalent The spatial distributions of shear wave velocities νs20 and νs30 have significant zoning characteristics, and the equivalent shear wave velocity limit νs30 of Class Ⅲ and Ⅳ sites with overburden thickness d> 80 m can be taken as 170 m / s. (2) The shear wave velocity of the soil layer in the plain area shows a power law function with the depth. After the hilly area is refined into three small areas, the shear wave velocity of the soil layer in each area shows a quadratic polynomial relationship with the depth. (3) The method of stepwise extrapolation has good applicability. However, when the shear wave velocity at the extrapolation depth changes violently, the stepwise extrapolation of the shear wave velocity will fail. (4) According to the stepwise extrapolation of shear wave velocity, we can get the Hrock of any hypothetical bedrock with the shear wave velocity of not less than 500 m / s and 700 m / s and the excellent period Tg of the corresponding micro-vibration site, The spatial distribution of values of Hrock is consistent with the spatial distribution of Hrock values. When the top of the soil with shear wave velocity of 700 m / s is the seismic basement, the differences of Tg and Hrock values of each engineering geological zoning are significant Increase.