Study On Finite-Difference Numerical Simulation And Radon Transform Of Tunnelseismic Prediction

In tunnel construction,there are always fault fracture zone,coal seam,karst,rich water and other bad geological problems.The tunnel advance prediction use geophysical method to obtain geological information in front of the tunnel face,which is important to ensure the construction progress and safety.Using computer to simulate the propagation process of seismic wave is not only helpful to understand propagation law and characteristics of seismic waves,but also provides a strong basis for the inversion and interpretation of tunnel seismic data.However,the ground seismic numerical simulation method cannot be applied to the complex environment simulation of the tunnel cavity.Therefore,the numerical simulation method and signal processing method for the tunnel seismic analysis have important theoretical and practical values for the detection mode,equipment development and data interpretation.In this thesis,the two-dimensional tunnel is modeled,the finite-difference method is used to simulate the seismic wavefield in the tunnel,and the response characteristics of seismic waves in different geological conditions are studied.The linear Radon transform is used to extract the reflected waves and separate the P-wave and S-wave,mainly completed the following work:(1)Starting from the wave equations established by the three basic equations of elastic mechanics,based on an arbitrary high-order staggered-grid finite-difference scheme,the staggered grid differential formula for the first-order velocity-stress equation is analyzed.The treatment of key problems in the finite-difference method is discussed,including source selection and loading,numerical stability,numerical dispersion,artificial boundary,and free boundary of the tunnel face and wall.(2)The basic formulas and properties of linear Radon transform,parabolic Radon transform,and hyperbolic Radon transform are studied.The principle of least square linear Radon transform in frequency domain and its higher resolution method are discussed.Taylor expansion of the reflection time-distance curve is studied,which help study the physical meaning of the linear Radon transform operator and the error of the nonlinear time-distance curve.The model is established to discuss the adaptability of the linear Radon transform used for the separation of reflected waves at different interfaces.(3)The finite-difference numerical simulation of tunnel seismic waves is implemented by programming the Matlab program.The wavefield characteristics and differences of seismic waves excited on the tunnel wall and the tunnel face are discussed and compared.The wavefield characteristics of faults,karst caves,and other unfavorable geologic bodies are simulated and analyzed based on the tunnel excitation method,which deepens the understanding of complex wavefields in the tunnel.Finally,the effectiveness of the linear Radon transform used to separate the P-wave and S-wave in the complex seismic data of numerical simulation is verified.(4)The engineering experiment is conducting in the Chongqing Jinyunshan tunnel with the TETSP-2 system,the application of wavefield separation in actual seismic data processing is analyzed to verify that it can extract the reflected waves and separate the P-wave and S-wave,and the final forecast result is consistent with the actual excavation situation.