Propagation Characteristics Of Excitation Wave In Mining Overburden And Inversion Of Mechanical Parameters

The scientific determination of mechanical parameters of coal mining overburden is the most basic and important subject of all rock engineering.Taking the propagation mechanism and mechanical characteristics of artificial shock wave in coal mining overburden as the research object,the topic has important theoretical value and practical significance.Based on elastic wave propagation theory,artificial excitation wave field characteristics and mathematical analysis in rock mass,the geometric and mechanical characteristics of mining-induced overburden fractures are analyzed and derived by forward(inverse)modeling and mathematical derivation.(1)A mechanical model of shear wave vibroseis under the combined action of vertical concentrated force and horizontal momentless force is established,a mechanical model of shear wave vibroseis under the combined action of vertical concentrated force and horizontal no-moment force that can simulate artificial excitation is established,the displacement field expressions of P wave,SV wave and SH wave in the model are derived,which revealed the mechanical mechanism of generating multi-wave by shear wave vibroseis.The in-situ test method of "three dimensional three component acquisition of VSP excited by S-wave vibroseis"suitable for mining rock mass was proposed,which is suitable for coal mine geological occurrence environment.The field experiment of shear wave vibroseis construction parameters and the study of seismic wave field characteristics are carried out.The unconventional seismic exploration and observation systems of zero offset VSP,Walkaway VSP and walkaround VSP are designed.The key acquisition parameters such as source spacing,maximum well source spacing,geophone spacing and time acquisition interval in VSP exploration are determined.Using the above research results,in-situ test and data acquisition of engineering characteristics in mining overburden of low-frequency seismic multi wave transmission are realized.(2)Based on the equivalent continuum theory,the flexibility tensor of multi-group fracture media and expression of tensor component of flexibility matrix of fracture system in orthotropic medium(OA)are derived,and the response characteristics of mining fracture geometry parameters,ground observation system and time difference of QP wave generated by artificial excitation are simulated by forward modeling,which include a single group of fractures,two groups of fractures and three groups of fractures.That provide a basis for the inversion of fracture azimuth,anisotropy and mechanical parameters.(3)Based on the solution method of perturbation theory of Christoffel equation in anisotropic media,this paper adopts Walkaround VSP acquisition and seismic wave separation technology,and uses the "five point trinomial fitting derivation method" to calculate the slowness vector,"covariance matrix method" to extract the polarization vector,and uses"pseudo transmission coefficient method" to obtain the amplitude value.That inverse the fracture strike and anisotropy coefficient of mining overburden and applied to engineering practice.(4)The mathematical expressions of qS2 slowness vector and polarization vector in completely anisotropic media are derived.A method of jointly inverting 21 elastic matrix coefficients by using the slowness vector and polarization vector of qP wave,qSl and qS2 wave is proposed.The elastic matrix coefficients,anisotropic parameters and engineering elastic parameters of mining overburden under complete anisotropy are inverted by using the minimum objective function method.