Wave Velocity Analysis Of Tunnel Seismic Prediction Based On The Polarization Method

Tunnel seismic prediction is a geophysical technology to obtain geological information in front of tunnel face,which plays an important role in ensuring the safety of tunnel construction.As one of the most widely used seismic exploration technologies,TSP system still has some defects in the speed analysis of data processing.The purpose of this paper is to propose a new way of velocity analysis.The main work of this paper is to apply the polarization analysis method to the velocity analysis,mine the potential information of multi-component seismic data,and propose an algorithm that can accurately calculate the wave velocity of the surrounding rock in front of the tunnel.The algorithm research has completed the following work:The basic principle of seismic wave finite difference numerical simulation is studied.The seismic wave equation is constructed from geometric equation,constitutive equation and Navier equation.And the staggered grid difference form of the equation is completed.The key problems of solving the difference equation are analyzed,including source loading,boundary condition of PML,numerical dispersion and stability research.Matlab program is compiled to complete the seismic wave forward numerical simulation of tunnel model.The basic principle of polarization analysis method is studied,and the algorithm of wave velocity analysis is proposed based on polarization analysis.The object of polarization analysis is multi-component seismic signal,and the signal collected by TSP system is three-component seismic signal suitable for polarization analysis method.The polarization analysis method based on standard covariance and adaptive covariance matrix is analyzed.And the polarization characteristic parameters are obtained by polarization method.The calculation method of velocity is obtained by combining the polarization azimuth and calculation formula of dip-moveout,and the algorithm of generating velocity spectrum by velocity scanning is proposed.The tunnel models of different unfavorable geological bodies are established,including fault models with different dip angles and karst models with different positions.The seismic signals of each model are simulated.The seismic wave signal collected by the models are substituted into the wave velocity analysis algorithm based on the polarization analysis method.The polarization azimuth and velocity from the velocity spectrum obtained by each model are consistent with the preset value of the model,which verifies the validity of the polarization velocity analysis algorithm.The algorithm is used to analyze the actual engineering data and reliable results are obtained.In this paper,the wave velocity analysis algorithm based on polarization analysis method is feasible,which has certain theoretical significance and practical value for TSP to accurately calculate the wave velocity of surrounding rock.