苏州城区场地等效剪切波速计算深度取值探讨

Discussion on calculation depth selection of equivalent shear wave velocity for site classification in urban area of Suzhou

鉴于场地等效剪切波速的计算深度是否需要由地表以下20 m增至30 m的争论尚未有定论,依据苏州城区场地143组实测剪切波速资料的统计分析,对GB50011-2010《建筑抗震设计规范》场地类别分类标准与欧美抗震设计规范场地分类标准进行了对比,比较了苏州城区场地等效剪切波速计算深度取为20 m和30 m的差异性,结果表明:苏州城区场地剪切波速在地表以下20～60m范围的变异性较大,采用分段函数描述剪切波速随土层深度的变化关系是合适的;III类场地等效剪切波速大小的分布偏向III类场地类别的下界限值,当计算深度由20 m增至30 m时,场地等效剪切波速的均值增大16%,如果直接沿用欧美规范的场地分类界限值,将会整体提高苏州城区场地类别的划分标准,苏州城区III类和Ⅳ类场地的等效剪切波速分界值取为170 m/s是适宜的。

In view of the question whether or not increasing the soil depth from 20m to 30m in calculating equivalent shear wave velocity for site classification is controversial,shear wave velocity data of 143 drilling holes from urban area of Suzhou are analyzed.By comparing site classification standards between GB50011-2010 code for seismic design of buildings and American and European seismic regulations,the differences of equivalent shear wave velocity calculated with the depth of 20 m and 30 m are discussed.The results show that shear wave velocity has much higher variability for soil depth of 20-60 m,the relationship between shear wave velocity and soil depth is fitting with piecewise linear function and power function.The sample values of equivalent shear wave velocity for site class Ⅲ is more close to the lower boundary value of site class Ⅲ.When the calculation depth increases from 20m to 30m,the mean values of equivalent shear wave velocity for the site class Ⅲ will increase 16%.Following the boundary values of site classification of American and European seismic regulation will improve classification standard for the sites in urban area of Suzhou integrally.If the calculation depth is increased to 30 m,it would be more appropriate to use 170 m/s as the boundary value of the site class Ⅲ and site class Ⅳ.