| In the construction and development of urban underground tunnels and other underground projects,shield tunneling machine construction methods are widely used due to their significant advantages such as high automation,fast construction speed,and high economic benefits.However,due to the complex and variable geological conditions of the shallow underground layer in cities and the complex environment of surface exploration,drilling and other methods are difficult to cover the entire tunnel project line,and it is difficult to fully explore the underground geological situation in the early stage.In this regard,it is urgent to carry out advanced geological prediction during tunnel construction,explore geological conditions,and carry out pre prevention and control,which is an important prerequisite to ensure the safe excavation of shield tunneling machines.Compared to traditional drilling and blasting methods for tunnel construction,the construction environment of shield tunneling machines is more complex.Traditional geophysical methods are limited by the space and environment inside the shield tunnel,making it difficult to achieve long-distance and high-resolution detection.In summary,conducting research on fine geological detection methods suitable for urban shield tunneling is an urgent need for the safety construction of urban underground tunnels.In response to the difficult problem of poor geological detection in urban shield tunneling,this article focuses on the utilization of shield tunneling noise sources and proposes an innovative approach for advanced detection of poor geological conditions based on the combination of shield tunneling source "ground hole tunnel" multi wave fields:using shield tunneling machine construction vibration as the source,observing the multi wave field information induced by excavation noise sources in the hole and on the surface,and jointly utilizing it,Effectively expanding the observation aperture of geophysical fields and increasing response wave field information,supporting and improving the accuracy of geological exploration ahead.Based on the above ideas,the characteristics of urban shield tunnels are combined with shallow surface multi wave field wave velocity inversion,with a focus on three research contents:"joint advance detection of multi wave field characteristics and observation methods of ’ground hole tunnel’,borehole tomography inversion method based on clustering constraints and multi virtual source stacking,and surface wave velocity inversion method based on tomography information prior".The research focuses on typical adverse geology of urban underground shield tunnel construction,Numerical simulation experiments were conducted to verify the feasibility of the detection method proposed in this paper.Finally,the practicality of the method was verified in projects such as the power tunnel of Guangzhou Power Supply Bureau.(1)Based on the joint advanced detection of multi wave field characteristics and observation methods of surface-drill-tunnel.In response to the limited observation system of traditional seismic exploration methods in shield tunnels,a joint observation method of borehole and surface reception is proposed using the excavation noise of shield tunneling machines as the source.Among them,the focus is on the problem of unclear understanding of the characteristics of excavation source wave fields observed in the borehole and surface.The characteristics of excavation vibration noise observed on the surface and in the borehole,as well as the virtual source wave field response law of unfavorable geology,were analyzed.Combined with the sensitivity of multiple types of wave fields to the detection target area in front of the shield tunnel,the selection of dominant wave field types was achieved;Furthermore,based on methods such as Fourier transform,frequency Bessel transform,and continuous wavelet transform,effective wave field information can be separated and extracted;On this basis,the optimal layout parameters of the "ground hole tunnel" joint observation system for shield tunneling were determined,achieving effective perception of adverse geological wave field response,and laying a data foundation for subsequent inversion of source surface wave and body wave velocities in excavation.(2)A borehole tomography inversion method based on clustering constraints and multi virtual source stacking.In response to the difficulty of obtaining the longitudinal wave velocity in front of the shield tunnel,a tomography imaging wave velocity inversion method was studied.A tomography inversion method based on clustering analysis constraints is proposed to address the issue of insufficient ray density in the hole tunnel transmission observation mode,which leads to low accuracy in the calculation results of traditional first break travel time tomography methods.The focus is on improving the inversion effect of tomography under sparse ray density conditions;Furthermore,based on the characteristics of continuous construction of shield tunnels,a surface-drill-tunnel multi virtual source reconstruction and ray stacking inversion strategy is proposed,supplemented by multiple excavation face virtual source records and surface virtual source records,to supplement the ray density in the detection target area;The combination of the above methods has improved the accuracy of calculating the wave velocity of geological structures in front of shield tunneling.(3)A surface wave velocity inversion method based on prior information from tomographic imaging.The problem of relying on the initial model and onedimensional wave velocity inversion in the process of surface wave inversion is addressed.In this regard,considering that the hole tunnel tomography method can obtain the horizontal variation characteristics of wave velocity,the wave velocity variation characteristics and stratigraphic stratification characteristics have been extracted from them,and they have been used as the initial model for surface wave inversion,effectively suppressing the problems of strong inversion multiplicity and low accuracy caused by inaccurate initial models;Furthermore,a surface wave velocity inversion method based on tomography inversion wave velocity prior was proposed,which achieved the joint utilization of surface wave and bulk wave field information and improved the accuracy of surface wave velocity inversion;On this basis,a surfacedrill-tunnel multi wave field joint implementation method for advanced detection of unfavorable geology has been formed,providing a reliable method for advanced detection of unfavorable geology in urban underground shield tunneling construction.On the basis of the above research,on-site tests were conducted on the Zengcheng South Power Tunnel project of Guangzhou Power Supply Bureau to obtain the wave velocity distribution of the rock and soil in front of the shield tunnel,verifying the feasibility of the method proposed in this paper. |
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