The Research On Numerical Simulation Of Forword Migration And Signal Analysis Processing Of Geophysical Prospecting For Unfavorable Geologic Bodies In Tunnels

So far tunnel geological prediction(TGP) has been developed for decades with many geophysical methods such as seismic reflection(TSP, HSP, land sonar),lectroma- -agnetic waves(GPR),electromagnetic induction methods(TEM). Tunnel geological prediction has made significant progress wholely, but some events reported wrongly appeared.This shows that TGP needs researched deeply on precious prediction.To make more precious prediction for TGP,geophysical signal processing associated needs researched,and sim- -ulation developed to understand geophysical methods better.In this paper,We model with seismic and GPR,and analyze geophysical signal which are all associated with TGP.In this paper,on the basis of previous research,we elaborate the method and com- -putation steps of forward and emigrant on f-k domain in detail.,implement it through programming(C),at the same time make emigrant on simple and complex model.Forward and emigrant proposed in this paper show that this is a method with fast computation velocity,stability,and adjusting to seismic model having chaging horizontal velocity, velo- -ocity,besides,through emigrant wave field is homing well,clearly image,the result of forward analyzed demonstrate that the phase of Longitudinal wave on hole with water and without water resemble each other,we also demonstrate seismic wave is not sensitive to water.The basic principles of GPR is elaborated in detail in this paper,analyzing itsValue on project,besides,on the basis of previous researcher,produce a new algorithm of Elec- -tromagnetic forward based on Finite difference.Implement the computation program through programming myself,The program can forward the model of any shape cont- -ainingεσμElec parameters,meanwhile output datas altenately. Carried out with the program and profile simulation of electromagnetic wave propagation characteristics of forward modeling, propagation of electromagnetic waves by visual maps and geological model in the tunnel complex in the forward spread of negative images and a variety of typical tunnel forward the results of geological bodies and Forward the results of the analysis summarized.We analyze and summary the actual radar data of geological geophysical signal, based on theoretical analysis, forward simulation.make the main conclusion as follow:Geophysical signal parameters and the main criterion below:1. Reflection phase characteristics : the phase of GPR is a precious parameter to qualitively judge adverse geological.For example negative phase for the high dielectric constant containing water,positive phase for low dielectric constant without water.2.The energy of reflection: the energy of reflection is a precious parameter to qua- -litively judge adverse geological.But reflect coefficient is hard to recovery due to the gain processing by instrument when collecting datas,so it is only a reference instead of precious computation.3.the shape of reflection:the shape of reflection event can reflect the shape of geol- -ogical,but affected by the chaging velocity and the diffraction wave of pinch point,the shape of reflection becomes distortion,and fuzzy,needing further imag processing.4.the frequency of reflection: When reflected wave in the face of high moisture content low conductivity media, the phenomenon of low frequency occurs .This is the classicsal character when in face of water. When interpretate the section produced bycommon processing method,pay attention to the following:1.The width error interpretated by fracture zone containing water.Because of com- -mon processing soft of electromagnetic is for constant velocity,this makes the width of fracture zone containing water longer which should be shorter when interpretated.2.The affect of conductivity:because of actual rock especially rock with water is high conductivity,they are not simpled to high impedience rock.The rock with high conductivity and water can makes electromagnetic waves energy attenuate sharply and quiet vacation area in the reflected wave turn out. This is needed for a comprehensive analysis and determineAt last,F-K emigrant method is used for GPR forward datas which is introduced from seismic.Before the emigrant the GPR datas are transformed for time.The result of emigrant eliminate the affect of diffraction and changing velocity,recovery the true shape of geological underground.