土层剪切波速与埋深关系统计分析和应用

APPLICATION AND STATISTICAL ANALYSIS OF RELATIONSHIP BETWEEN SHEAR WAVE VELOCITY AND DEPTH OF SOIL-LAYERS

一般认为土层剪切波速与埋深关系的回归公式主要用于对当地土层剪切波速值的初步估计。为了提高钻孔波速测试数据的应用价值,基于土层剪切波速与埋深关系的主要数学模型及其拟合参数,推导了场地覆盖层厚度计算公式、等效剪切波速计算公式和时深转换中反射波组埋深计算公式。以河南省长垣县场地为例,采用上述新公式计算获得的场地覆盖层厚度值、等效剪切波速值可满足工程需要。并提出应用这些新公式的步骤为:1)依据场地相关资料划分地震工程地质单元;2)对同一个地震工程地质单元内的钻孔波速测试数据进行统计分析,综合判别和选择土层波速与埋深统计关系的数学模型及其拟合参数;3)将选择的数学模型的拟合参数分别代入上述的新公式,即可分别获得场地覆盖层厚度、等效剪切波速或地层反射波组埋深。

The shear wave velocity is one of the important parameters in seismic engineering. The common mathematical models of relationship between shear wave velocity and depth of soil-layers are linear function model,quadratic function model,power function model,cubic function model,and quartic function model. It is generally believed that the regression formulae based on aforementioned mathematical models are mainly used for preliminary estimation of the local shear wave velocity. In order to increase the value of test data of wave speed in boreholes,the calculation formulae for the thickness of ground cover layer are derived based on the aforementioned mathematical models and their fitting parameters. The calculation formulae for the mean shear wave velocity of soil-layers are derived by integral mean value theorem. Accordingly,the calculation formulae for the equivalent shear wave velocity of soil-layers are derived. The calculation formulae for the depth of reflective waves in time-depth conversion of the reflection seismic exploration are derived. Through the statistical analysis of test data of shear wave velocity of soil layers in Changyuan County,Henan Province,regression formulae and their fitting parameters of aforementioned mathematical models are obtained. The results show that in the determination of the quality of these regression formulae and their fitting parameters,the adjusted R- square,root mean square error and residual error,the matching on the statistical range between the geometry of function of mathematical models used and the scattergram of the measured data,the application purpose and the simplicity of the regression formulae should be considered. With the aforementioned new formulae,the results show that the calculated values of equivalent shear wave velocity of soil-layers and thickness of ground cover layer meet the engineering needs. The steps for statistics and applications of the relationship between shear wave velocity and depth of soil-layers for a new area are as follows：（ 1） Analyze the relevant data about the site such as the drilling and wave speed test data,etc. and divide the site into seismic engineering geological units;（ 2） In a single seismic engineering geological unit,make statistical analysis of the data of borehole wave speed test,comprehensively identify and select mathematical models and their fitting parameters of the relationship between shear wave velocity and depth of soil-layers;（ 3） Substitute the selected fitting parameters into the formulae,based on their mathematical models for the thickness of ground cover layer,or the equivalent shear wave velocity of soil-layers,or the depth of reflective wave,then the thickness of ground covering layer,equivalent shear wave velocity,and depth of reflective wave are obtained.