| TBM(Tunnel Boring Machine)construction method is widely used in the construction of long and large tunnels due to its advantages such as fast excavation speed,high quality of cave formation,economic benefits and safe.However,TBM has poor adaptability to adverse geological bodies and complex strata.If the geological conditions in front of the tunnel face were not detected in time and corresponding treatment measures were not taken,it is easy to cause abnormal tool wear and cutter head damage and other consequences.In severe cases,it may even cause serious engineering accidents such as TBM blocked,scrapped and construction personnel injury and death.Therefore,it is very necessary to carry out advanced geological prediction in advance during TBM construction,to detect and deal with adverse geological bodies in time,to ensure the safe and efficient tunneling of TBM.TBM construction method has large mechanical structure,tight process connection,fast driving speed.This makes short allowable detection time,narrow available detection space,bringing great difficulties to the application of traditional tunnel advanced detection method.The seismic while tunneling using TBM drilling noise adopts the idea of "changing noise as the source".It can predict the adverse geological bodies such as faults and karst caves in front of the tunnel real-time along with the TBM excavation.However,the existing data processing methods of rock breaking focus usually pay attention to the interface imaging of adverse geological bodies,ignoring the inversion of wave velocity,and directly use the wave velocity of the tunnel face.On the one hand,it is difficult to realize the dual parameter geological interpretation of wave velocity and interfaces;on the other hand,the accuracy of imaging is limited due to the inaccurate wave velocity.Therefore,it is necessary to study the accurate calculation method of wave velocity for TBM rock breaking source detection,optimize the imaging effect of reflection interfaces,and realize the joint interpretation of wave velocity and interface.In order to solve the above-mentioned problem of low accuracy of velocity distribution and reflection interface imaging of the seismic while tunneling using TBM drilling noise,this paper adopts the methods of theoretical analysis,numerical calculation,and field test to apply the high-precision inversion and imaging of the seismic while tunneling using TBM drilling noise.This paper develops the cross-correlation seismic interferometry method,the full waveform inversion method,and the reverse time migration imaging method.Full waveform inversion and reverse time migration imaging processing are systematically carried out.According to the typical adverse geological conditions of the tunnel,the systematic numerical simulation and processing analysis are carried out,and the corresponding inversion imaging characteristics are summarized.Finally,this method has been verified in the field engineering.The main research work and results of this paper are as follows:(1)Cross correlation seismic interferometry method based on wavelet estimation and waveform correction.Common seismic interference methods are compared and the relatively stable cross-correlation interference is selected to process the detected data by the seismic while tunneling using TBM drilling noise.The overlapping time window and windowed spectrum estimation method are used to improve the recovery effect of virtual source seismic records.On this basis,to solve the problem that the accuracy of amplitude and phase information of virtual source seismic records obtained by seismic interferometry is poor,the wavelet extraction algorithm based on high-order cumulants is used to extract the wavelet of virtual source records,and the waveform correction of virtual source seismic records is carried out according to a reference wavelet.Then the virtual source seismic records with Ricker wavelet as the source wavelet are obtained,which provides reliable data for subsequent processing(2)Tunnel full waveform inversion method based on wave velocity correction and regularization.Full waveform inversion is a recognized high-precision wave velocity inversion method,but the initial wave velocity model is required to be close to the real wave velocity model.In this paper,a full waveform inversion method based on multiple integral transform wave field and normalized integral objective function is proposed,which can achieve good inversion effect under poor initial model.The single shot active source detection data in tunnel is too small and the offset is too small,which will lead to the multi-solution problem of full waveform inversion.Therefore,this paper assumes that the wave velocity changes gently in the geological structure in front of the tunnel face,and the wave velocity changes sharply between geological structures.Based on this,the wave velocity correction and regularization methods are proposed,which are introduced into tunnel seismic full waveform inversion,to reduce the multi-solution problem of inversion and improve the effect of wave velocity inversion.(3)Reverse time migration imaging method based on inverted wave velocity distribution and coherence factor.Reverse time migration imaging is a high-precision imaging algorithm for reflection interface.Its imaging accuracy depends on the wave velocity model and is often accompanied by low-frequency noise.In this paper,the full waveform inversion is used to provide a more accurate wave velocity model,which improves the positioning accuracy of reverse time migration imaging.The main frequency of rock breaking source data is low,so the imaging results have low resolution.Therefore,the coherence factor correction method is used to improve the resolution of imaging results.(4)The full waveform inversion and reverse time migration imaging method of the seismic while tunneling using TBM drilling noise based on the joint processing of multiple exploration data in close range.Combining the first three research contents,the full waveform inversion and reverse time migration imaging method of the seismic while tunneling using TBM drilling noise are achieved,and finally the adverse geological bodies in front of the tunnel are depicted with more accurate position and shape.At the same time,the multiple detection data of the seismic while tunneling using TBM drilling noise in short distance are jointly processed to improve the stability of full waveform inversion and reverse time migration imaging,and obtain better inversion and imaging results.Systematic numerical simulation tests are carried out for typical unfavorable geological bodies in tunnels.The inversion and imaging characteristics of typical unfavorable geological bodies are revealed,and preliminary geological interpretation criteria are proposed.Based on the above research results,the actual measured data of Jilin Songjiang Water Diversion Project,a project in Xinjiang and Gaoligongshan Project in Yunnan are used to carry out the test verification.The effectiveness and reliability of this method are verified by the successful inversion and imaging of faults and rock mass fracture in front of the tunnel face. |
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