Research On Structure Characteristics Of Shallow Soil Layer In Jianghan Basin Based On The Microtremor Survey Method

The Microtremor Survey Method is a geophysical detection method using site background noise as a signal source.The method has the advantages of no interference with the site,simple and fast,and can be used for rapid strata detection in residential areas,highways,and environmentally sensitive areas,and has been rapidly popularized and applied in recent years.However,whether the accuracy of stratigraphic division meets the engineering geology requirements has always been an important issue in geophysics and geotechnical engineering.The article first reviews the research progress of wave exploration technology domestic and foreign.The Microtremor Survey Method based on the spatial autocorrelation method is summarized,including the collection of data,analysis of spectral features,calculation of spatial autocorrelation coefficient,extraction of dispersion curves,initial model setting and inversion of stratigraphic structure.Through the experiment of three different arrays at the scene,the results of the experimental site were obtained.Finally,compared with borehole core data under the same site,the feasibility of the Microtremor Survey Method in the strata structure detection in Jianghan Basin was verified.Through the Microtremor Survey Method in the Jianghan basin,the following conclusions are obtained:(1)Under the conditions of balanced work efficiency and experimental accuracy,in acircular array,when one detector is set in the center and three detectors are set inthe circumference,it is an optimal method of observation.The array can also bechanged to combine triangles with different radii,to form multiple rings array;(2)In the experimental process,a total of three types of arrays of triangular,T-shaped,and L-shaped were set.The dispersion curves of triangular,T-shaped and L-shapedextractions are nearly identical,which verifies the feasibility of ESPAC method inthe Microtremor Survey Method;(3)The inversion results show that the ground of the experimental site can be dividedinto 5 layers from top to bottom.The depth of the first layer is approximately 20 m,the shear wave velocity is approximately 200m/s;the depth of the second layer isapproximately 50 m,the shear wave velocity is approximately 350m/s;the depth ofthe third layer is approximately 100 m,and the shear wave velocity is approximately500m/s;The depth of the layer is approximately 190 m,the shear wave velocity isapproximately 750 m/s;the depth of the fifth layer below 210 m,and the shear wavevelocity exceeds 750 m/s;(4)Compared with borehole data,the SPAC method has good accuracy for thestratification of the site.Especially the soil-rock interface in the stratum,the SPACcan be distinguished very effectively;The Jianghan Basin has a relatively thick stratum thickness,little change in local undulations,and relatively simple stratigraphic properties.This provides some convenience for the Microtremor Survey Method,and the experimental results also show that the Microtremor Survey Method has this higher resolution and accuracy,which provides a certain theoretical and practical basis for the promotion of the Microtremor Survey Method in Jianghan Plain in the future.