Analysis Of Elastic Wave Propagation Characteristics Of Typical Small Geological Structure In Coal Measure Strata

The geological structure of coal measures strata is complex and changeable,which will affect the exploration of elastic wave. The purpose of this dissertation is to analyze the influence of the small structure on the propagation of elastic waves,and to provide the basic theoretical support for the detection of elastic waves in the coal measure strata.According to the theory of elastic wave propagation, the channel characteristics of coal measure strata and the characteristics of minor faults, the small collapse column and goaf,this dissertation establishes propagation model of elastic waves in the minor faults, small collapse column and mined out areas by using different methods. The propagation characteristics of elastic wave in minor fault,small collapse column and goaf are analyzed. The main work of the dissertation are summarized as follows:(1)Channel characteristics of coal measure strata are analyzed. Combined with the theory of reflection,transmission and attenuation of elastic wave,this dissertation analyzes the characteristics of the layered strata, waveguide, filtering and multipath effect, which can provide theoretical basis for analysis of elastic wave propagation.(2)The dissertation analyzes the characteristics of small fault, small collapse column and the mined out area.This paper briefly introduces the types of small structure in coal measures strata and analyzes the characteristics of small fault, small collapse column, mined-out area, which provided the basis to explore the influence of the small fault, small collapse column and mined-out area on elastic wave propagation.(3)The finite element method is used to simulate the propagation of elastic wave in coal measure strata with minor faults and the propagation characteristics are analyzed.The paper establishes the fracture anisotropic equivalent medium model,derives the anisotropic elastic wave equation of displacement and simulates the propagation of elastic wave using finite element method.The filtering characteristics of elastic wave propagation in small faults are analyzed. The influence of break distance on propagation of elastic wave is analyzed.(4)The propagation model of elastic wave in small collapse column is established. Based on this model, the influence of small collapse column on elastic wave propagation is simulated and analyzed.The cylindrical small collapse column is chosen as the geometric model and the equivalent medium model is established. On this basis,this dissertation derives the reflection coefficient and transmission coefficient of various kinds of waves propagating in a small collapse column, and establishes the displacement function model of reflected wave and transmitted wave.The results using MATLAB are compared with the results of COMSOL finite element simulation to verify the rationality of the model. The influence of incident angle and source frequency on reflection coefficient and transmission coefficient of various kinds of waves is analyzed.(5)The dissertation establishes the transfer function of elastic wave in mined out area.The equivalent medium model of mined out area is established, and the propagation model of elastic wave in mined out area is established. With MATLAB simulation,the filtering characteristics of elastic wave in mined out area are analyzed.