Analysis Of Soil Shear Wave Velocity Based On Relatived Reference Point Spectral Ratio Method Of Borehole Microtremor

Shear wave velocity of site soil layer is an important parameter in the field of geotechnical engineering.It is an important basis for classification of construction sites,analysis of site seismic response and discrimination of foundation saturated sand liquefaction.Finding a simple and efficient wave velocity testing method has become a concern in the field of engineering.Single-hole method and cross-hole method can accurately measure the wave velocity in the soil layer of the site,so they are widely used in engineering.However,these methods have the disadvantages of requiring artificial excitation on the surface and being greatly affected by the environment.In recent years,the method of analyzing the wave velocity structure of the soil layer at the site by using the ground pulsation information has developed rapidly.In this paper,the self-developed BMT-I and BMT-II test equipment are used to test the borehole ground pulsation.As a comparison,the single-hole shear wave velocity test of the same borehole is completed,and the relationship between borehole pulsation data and shear wave velocity is analyzed.The paper mainly includes the following contents:(1)A method for processing ground pulsation data,Spectral Ratio Method of Relative Reference Points in Holes,is proposed.Based on the theoretical model of borehole pulsation experiment and the assumption of vertical upward propagation of ground pulsation,the basic formula of relative reference point spectral ratio method in borehole is derived.The spectral ratio of the ground pulsation response spectrum of the measuring point in the borehole and the reference measuring point in the adjacent borehole is analyzed,and the velocity amplification effect parameter of the soil layer between the two measuring points is determined.Compared with the relative reference point spectral ratio method,the pulsating signal collected by this method is less disturbed by the environment and the selection of reference points is not limited.(2)The field measurement of the project has been completed in the Donglaijun community,the west of Deshangshijia,Qingxiang Road,Sunjiatan,Laishan District,Yantaicity.First of all,the site was inspected,and two adjacent boreholes were selected based on the geological survey data of boreholes.The depth of one borehole was 7m as a reference measuring point,and the other borehole was tested layer by layer from bottom to top as a test borehole.As a comparison,the single-hole shear wave velocity test of the same borehole was completed.(3)The relative reference point spectral ratio method in the hole was used to analyze the data obtained from the test.The obtained spectral ratio curve shows that the amplitude of the curve tends to be stable in a frequency range.The parameters of amplification effect of each layer of soil layer can be obtained by screening the stability value of the stable section of the spectral ratio curve.The nonlinear mathematical fitting method is adopted to compare with the wave velocity test results of single hole method,and the fitting results with higher accuracy are obtained.The obtained velocity amplification value is substituted into the fitting formula for inverse calculation to obtain the inverse wave velocity,and the average relative error is 17.3% compared with the wave velocity of single hole method.