Research On Detection Technology Of Loose Accumulation Based On Micro-Motion Method

There are mostly mountains in our country,and a large number of projects are in the alpine valleys.There are a large number of loose accumulations in the alpine valleys.Finding out the distribution of loose accumulations is of great significance to engineering design and safety assurance.Because of the irregular structure and distribution of loose accumulations,it is difficult to implement traditional geophysical exploration methods such as electrical methods and geological radars.The micromotion method is not restricted by site environmental conditions,has strong antiinterference ability,and has a wide range of applications.The characteristics of the micro-motion method has a huge advantage in detecting such accumulations.Micromotion detection technology refers to a geophysical method that extracts the Rayleigh surface wave dispersion curve information from the natural field source micro-motion signal,and then inverts the dispersion curve to obtain the shear wave velocity structure of the formation.The main factors affecting the accuracy of the micro-motion results are the quality of the collected data,the accuracy of the dispersion curve extraction,and the accurate inversion of the dispersion curve.At the same time,some low-speed interlayers or high-speed interlayers are often included in the accumulation,which also interferes with the accuracy of the micro-motion detection method,which causes large errors in this method in many cases.Aiming at the main points and problems of the micro-motion method in detecting loose accumulations,this paper makes a forward analysis of the influencing factors of surface wave dispersion curves based on the generalized reflection-transmission coefficient algorithm,and analyzes the geological and geophysical characteristics of loose accumulations.The spatial autocorrelation method explores the blind spot law of the micro-movement method when detecting loose accumulations and does a detailed study on how the micro-movement method can be implemented in actual projects.The main research contents and results of this paper are as follows:1.The forward algorithm of surface wave and dispersion curve in layered media(generalized reflection-transmission coefficient algorithm)is studied,and the main frequency,layer thickness,density,vertical and horizontal wave velocity and shear wave velocity versus surface wave dispersion curve are analyzed.It is concluded that the most important factor affecting the surface wave dispersion curve in layered media is the shear wave velocity,followed by the thickness of the formation,while the longitudinal wave velocity,density and dominant frequency have little influence on the surface wave dispersion curve.2.From the perspective of genesis,the loose accumulations are divided into four categories,and the geological and geophysical characteristics of the three common types of loose accumulations in engineering are analyzed,and the corresponding geological and geophysical models are given.3.This article derives the spatial autocorrelation function of the spatial autocorrelation method in detail,and uses the spatial autocorrelation method to study the three common situations of loose accumulations(soft top and bottom hard,lowspeed interlayer and high-speed interlayer).The response characteristics of wave dispersion curve,and through the combination of forward model and reality,we explored the empirical law of whether low-speed interlayer and high-speed interlayer can be detected by the micro-motion method when detecting accumulations.The understanding is as follows:(1)The standard model of upper soft and lower hard: For covering layers with different thicknesses,as the thickness of the covering layer increases,the energy in the low frequency range is less abundant,and the span of the energy cluster is gradually decreasing.(2)Containing low-speed interlayer: When the buried depth of the low-speed interlayer/layer thickness of the low-speed interlayer>4.2,the low-speed interlayer cannot be measured.When the buried depth of the low-speed interlayer ? the layer thickness of the low-speed interlayer <4.2,the low-speed interlayer can be measured.(3)Containing high-speed interlayer: When the buried depth of the high-speed interlayer/layer thickness of the high-speed interlayer is less than 2.7,the high-speed interlayer can be measured.When the buried depth of the high-speed interlayer/the high-speed interlayer is >2.7,the high-speed interlayer cannot be measured.4.This article starts with the selection of micro-motion array,field observation,Butterworth filtering,extraction of dispersion curve and genetic algorithm inversion to study the realization process of micro-motion method,and applies it to the bank of a reservoir of a hydropower station in Tibetan area.During slope detection,the stratum structure reversed by the genetic algorithm was compared with the borehole data,and the effect was relatively satisfactory.