Multi-parameter Simultaneous Inversion Imaging Of Tunnel Advanced Detection Using Time-domain Induced Polarization With Cross-gradient

In the 21st century,as China’s national strategies such as "Western Development"and "Rise of Central China" are vigorously promoted,a number of major infrastructure projects have been put on the agenda one after another.And the number of difficult tunnels such as cross-river(river,sea)tunnels,extra-long and deeply buried mountain tunnels.The number of construction projects is gradually increasing,which brings valuable opportunities for technical research on tunnel construction,and also puts forward higher requirements for adverse geological forecasting.Numerous engineering practices show that tunnel construction often faces extremely complex geological conditions,especially when crossing karst strata and water-rich strata.It is very easy to induce water and mud bursts and other geological disasters,which seriously threaten the lives of people and property safety.It is an important prerequisite to avoid geological hazards and ensure the safety of tunnel construction to identify the adverse geological conditions in front of the tunnel,while water-bearing structures as the source of sudden water and mud hazards,there is an urgent need to carry out detection and location identification research related to them.In order to identify and locate the water-bearing structures in front of the tunnel palm face,time-domain induced polarization multiparameter inversion is an effective tool,which has been studied at home and abroad.①Time domain induced polarization forward mostly adopts time-frequency conversion,which is a tedious process and consumes a lot of computational time cost,while the time domain cole-cole expression contains an infinite number of steps and has poor computational convergence.②The time window of individual time window inversion is fragmented,and it is difficult to fit the inverse full time domain curve with large error,and there is no study on cross-gradient inversion of four parameters of induced polarization.③There are differences in the results of separate identification of multiple parameters,and no identification method is seen that considers four time-domain induced polarization parameters simultaneouslyAccordingly,this paper proposes the general solution of "cross-gradient-based multi-parameter simultaneous inversion imaging of tunnel full time domain induced polarization with water-conducting structures",with the "cross-gradient-based multi-parameter simultaneous inversion method" as the core."Theoretical analysis,numerical simulation and engineering validation are used to construct the multi-parameter simultaneous inversion imaging objective function and optimize it according to the inversion results to realize the multi-parameter identification of anomalies.The main research works and results of this paper are as follows.(1)Full time domain induced polarization overdetection forward method and acceleration algorithm in tunnel.In order to solve the problem of complicated time and frequency conversion steps of full time induced polarization forward,we propose the tunnel full time induced polarization forward detection forward method based on filtering algorithm;meanwhile,to solve the problem of many windows and long time for full time induced polarization forward calculation,we introduce array mapping method for node storage to realize fast node finding,and introduce OpenMP parallel algorithm to realize fast tunnel full time induced polarization,which effectively improves the efficiency of the full time induced polarization.(2)Multiparameter simultaneous inversion method for full time domain induced polarization based on cross-gradient.The cross-gradient-based multi-parameter simultaneous inversion method is proposed to address the problems of large errors and difficulty in fitting the full time domain curves due to window splitting in the separate inversion of the time domain induced polarization.For the problem that the sensitivity of each parameter to the anomalies in the inversion process is inconsistent and the inversion contribution needs to be balanced,a differentiation constraint is imposed on the sensitivity matrix of different parameters,and the effectiveness of the method is verified by combining numerical calculations,which achieves more accurate identification of the anomalies’ morphology and location,improves the multi-parameter simultaneous inversion effect,and forms a multi-parameter optimal inversion method based on the weighted constraint of the sensitivity matrix.(3)Multi-parameter identification method of tunnel full time domain induced polarization based on clustering analysis.In view of the fact that there are still differences in the inversion imaging parameters reflecting the boundary and scale of anomalies and it is difficult to accurately identify the anomalies and their boundaries,a multi-parameter identification method based on cluster analysis of tunnel full time domain induced polarization is carried out to achieve the identification of tunnel full time domain induced polarization overdetection anomalies.On this basis,the cross-gradient-based multiparameter simultaneous inversion imaging method of tunnel full time domain induced polarization overdetection was verified in the central Shanxi diversion project and the Gaoligongshan tunnel project of the Dareh railroad.The field tests show that the inversion imaging results are in good agreement with the excavation conditions,which verifies the feasibility of the method.