基于地貌单元的北京地区场地V_(S30)分类研究

Study on the classification of site V_(S30) based on geomorphic units in Beijing

工程场地30 m等效剪切波速(V_(s30))是衡量场地放大效应的一个重要参数。通过收集北京地区1:100 000精度地貌图、北京地区419个工程场地钻孔资料,统计了每一个实测孔的V_(s30)值。对每一类地貌下包含的钻孔资料,选取高程、地形坡度和到山的距离3个因素作为影响一类地貌单元V_(s30)的因子,进行多元线性回归分析,得到不同地貌单元属性的区域性V_(s30)估算公式。根据估算值与实测值间的残差,通过插值得到区域性的残差分布结果。将残差分布结果与估算V_(s30)结果叠加,得到区域性V_(s30)修正结果。再根据美国国家减灾计划(NEHRP)的场地分类结果对基于回归模型的V_(s30)结果、修正后的V_(s30)结果分别进行场地分类,经对比认为修正后的场地分类结果正确率高于修正前的结果。该方法及得到的认识对于工程场地分类、地震动作用下场地放大效应的估计和震后地震灾害评估,都具有一定的实用价值。

The average shear velocity down to 30 m(V_(s30))is an important parameter to measure the site amplification effect. By collecting a 1:100 000 geomorphology map of Beijing and 419 logging data,the V_(s30)of each borehole was calculated. For the borehole data contained in each type of landform,three factors,elevation,slope,and distance to the mountain,are selected as the factors affecting the type of landform V_(s30). Multivariate linear regression analysis was conducted to obtain the regional V_(s30)estimation formula for a different geomorphic type. According to the residual between the estimated value and the measured value,the regional residual distribution results are obtained by interpolation. The regional V_(s30)correction results are obtained by superimposing the residual distribution results and the estimated V_(s30)results. According to the site classification results of The National Disaster Reduction Plan(NEHRP)of the United States,the V_(s30)results based on the regression model and the revised V_(s30)results were classified respectively. By comparison,the accuracy rate of the revised site classification results was higher than the former results. The results have certain practical value for site classification,site amplification effect estimation,and post-earthquake disaster assessment.