Tunnel Permeability Prediction And Water Inflow Estimation Method Based On Time-domain Induced Polarization Relaxation Time

With the rapid and continuous development of my country’s national economy,huge demands have been placed on cross-regional allocation of water resources,hydropower development,and transportation construction.A large number of major infrastructures such as water conservancy and hydropower projects,railway and highway transportation projects are being or will be constructed.At present,my country has become the country with the largest tunnel(road)construction scale,the fastest development speed,and the most difficult construction in the world.However,with the planning and construction of many national-level major projects,the difficulties and challenges faced by tunnel construction have become increasingly prominent.Complicated geological conditions and extreme occurrence environments have become the main problems restricting tunnel construction,and the water and mud inrush disasters seriously threaten the safe construction of tunnels.The distribution of surrounding rock permeability is an important basis for the prediction and estimation of tunnel water inflow.However,the existing permeability prediction model has low prediction accuracy and applicability,and the permeability prediction model for the tunnel environment has not been established yet.The current water inflow estimation method needs to be estimated based on the preliminary geological survey data,and the results are quite different from the actual.Accurate prediction of the permeability is the key to the tunnel water inflow,and the tunnel permeability distribution obtained by the geological survey data is quite different from the actual one.How to integrate the hydrogeological parameters of the tunnel environment,establish a highly accurate and applicable permeability prediction model,and how to accurately obtain the permeability distribution information in front of the tunnel,and improve the accuracy of water inflow estimation are two key problems facing now.Aiming at these two key problems,the study of tunnel permeability prediction and water inflow estimation methods based on the time-domain induced polarization relaxation time was carried out.In response to the above problems,this paper takes the establishment of the induced polarization permeability prediction model,the realization of the tunnel permeability prediction and the estimation of the water inflow as the main goals,and the use of physical experiments,theoretical analysis,inversion research and engineering verification methods to develop typical tunnel lithology In the induced polarization permeability experiment of rock samples,a permeability prediction model based on the induced polarization relaxation time was established,and the formation factors and ion concentration parameters were integrated to optimize the model,which improved the applicability and accuracy of the model.Through reparameterization of the Cole-Cole model and the hydrogeological information as the constraints of the inversion inequality,the inversion of the permeability of the surrounding rock of the tunnel is realized.On this basis,a water inflow estimation method based on prediction of permeability was proposed,and engineering verification was carried out in Gaoligongshan Tunnel of Yunnan Darui Railway,and the water inflow was predicted to meet the engineering needs.The main research work and results of this paper are as follows:(1)Induced polarization-permeability test of typical rock samples.Using artificial sandstone core as the test material,an induced polarization-permeability test was carried out,and the relationship between induced polarization parameters and permeability was studied.The experiment found that there is a strong positive correlation between relaxation time and permeability.Relaxation time is selected as the main characteristic parameter of permeability prediction,which lays the foundation for the establishment of the subsequent induced polarization relaxation time permeability prediction model.(2)Permeability prediction model incorporating formation factors and ion concentration.First,in view of the difficult problem of predicting the permeability distribution of the surrounding rock of the tunnel,a model of the relationship between the induced polarization relaxation time and the permeability is established.At the same time,in order to improve the accuracy and applicability of the prediction model,two parameters,formation factors and ion concentration,were introduced,which improved the applicability and accuracy of the prediction model and laid the foundation for realizing the prediction of tunnel surrounding rock permeability.(3)Permeability prediction and water inflow estimation based on the reparameterized Cole-Cole model.By reparameterizing the Cole-Cole model,the relaxation time parameter in the Cole-Cole model is replaced by the permeability parameter,which provides model support for the direct inversion of tunnel permeability.Based on the cross-gradient inversion method,the hydrogeological parameters are introduced as the unequal constraints of the inversion,which suppresses the ambiguity of the inversion,and establishes a surrounding rock permeability evaluation method suitable for the tunnel environment.Based on the inversion analysis of the permeability distribution of the surrounding rock of the tunnel,combined with the classic empirical formula of the tunnel water inflow,a method for estimating the water inflow based on the prediction of permeability is proposed.(4)Engineering verification and improvement and optimization of permeability model.The permeability prediction model established by the laboratory needs to be determined on-site according to the actual project.Relying on the Gaoligongshan Tunnel of Yunnan Darui Railway,the project verified the induced polarization permeability prediction model,the inversion method and the tunnel water inflow estimation method.The tunnel surrounding rock sampling and water quality analysis have obtained parameters such as tunnel formation factors and ion concentration,and realized the optimization of the permeability prediction model in practical engineering applications.The results show that the prediction model and inversion method can better realize the distribution prediction of the water-bearing structure in front of the tunnel.At the same time,the tunnel water inflow is estimated based on the empirical formula,which is basically consistent with the water inflow revealed by the tunnel excavation and practicality.