Analysis Of Soil Shear Wave Velocity Based On Borehole Microtremor

Soil shear wave velocity is an important parameter for site classification,seismic microzonation,seismic response analysis and liquefaction discrimination of saturated sand,in the engineering field,seeking a convenient,economical and reliable method for testing the soil shear wave velocity has always been one of the hot issues.In recent years,although the shear wave velocity testing technique has been developing continuously,the single-hole method is still widely used in engineering,because it can reliably test the share wave velocity of soil layer.Nevertheless,there are some limitations in single-hole testing,such as artificial excitation of shear waves on the surface and limited testing depth.At present,the inversion of soil shear wave velocity using surface microtremor has attracted wide attention.In this paper,self-developed BMT-I borehole microtremor testing equipment is used to test the deep soil microtremor in boreholes,and the relationship between borehole microtremor and soil shear wave velocity is analyzed.The main research contents and obtained achievements in this paper as follows:(1)A new method of microtremor data processing,the Surface Reference Point Spectrum Ratio Method(SRPSRM)is proposed.On the basis of the existing data processing methods of microtremor,the basic formula of the SRPSRM is defined in combination with borehole microtremor experimental model.The method can obtain the dynamic characteristics of soil layers between measuring points by spectral ratio analysis of surface and borehole points response spectrum.Finally,this paper analyzed the feasibility of the SRPSRM to deal with borehole microtremor,and further discussed the principle of this method to be used in the analysis of soil shear wave velocity.Compared with the relative reference point spectral ratio method,the selection of reference points in this method is not restricted by site conditions.(2)The test of borehole mirotremor and soil share wave velocity at two sites of Yantai Evergrande Yushan Huafu and Longfor Phase IV Project has been completed.The analysis of borehole microtremor by SRPSRM shows that the amplified spectrum curves obtained bySRPSRM tends to be fixed in a certain range of the site excellent frequency.By comparing and analyzing the parameters of spectral comparison curves with the shear wave velocities tested by single-hole method,the mathematical fitting method was used to establish the relationship between them,and the fitting results with high goodness of fit were obtained.(3)The applicability of the function relation is verified by the tested results of Donglai County Project site.By comparing and analyzing the results of wave velocity inversion with those of single-hole method,the results show that the shear wave velocity obtained by this method can serve in the actual engineering problems.