Study On Creep Parameter Inversion And Supporting Time Of Surrounding Rock In Deeply Buried Water Diversion Tunnel

Deep,long and large hydraulic tunnels emerge one after another with the continuous development of large-scale water resources allocation projects,the tunnel construction and operation safety is affected by many factors such as geological environment and construction method,in order to ensure the safety of the tunnel,this paper established a numerical simulation model,which accord to the actual construction process of the tunnel,and then inverted the surrounding rock parameters based on the monitoring data,and then based on the obtained parameters,research the supporting time of initial support and secondary lining of the tunnel.The main research contents are stated as follow:（1）Established the 3D tunnel construction numerical simulation model with the FLAC^3D finite difference software.Based on sensitivity analysis method,elastic modulus and four creep parameters were determined to be inverted.The numerical model is used to calculate the different parameter combinations of orthogonal experimental design,and the corresponding displacement values of every parameter combination are obtained.The RBF neural network was trained to form the displacement values and parameters mapping relationship,and the elastic modulus and four creep parameters of Burgers model were obtained by monitoring displacement values.By comparing the calculated displacement values and the monitored displacement values,the parameter inversion results have small error and high inversion accuracy,which indicates that the parameter inversion method is reasonable and feasible.Finally,based on the inversion parameters,simulated the construction process of deep-buried diversion tunnel and then analyzed that.（2）Based on the inversion parameters,study the initial supporting time of the tunnel.The influence of excavation length,step height and lateral pressure coefficient on the tunnel initial supporting time is studied.The 2D and 3D numerical models were established respectively.In the 2D model,use the corresponding displacement increment to get the best initial supporting time,the stress release rate was integrated,and the corresponding comprehensive displacement completion rate was obtained.Through the same comprehensive displacement completion rate in the 3D model,finally,the initial supporting time was given based on the distance between the excavation face and the initial support.The comprehensive stress release rate and comprehensive displacement completion rate can avoid the influence of different measurement points on the results and can improve the rationality of initial supporting time selection,and provide reference for practical engineering.（3）Based on the inversion parameters,study the secondary lining time of the tunnel.Calculate the secondary lining construction at different time after the tunnel excavate and the initial support.analysis the tunnel surrounding rock displacement,and the initial support stress and displacement,and the secondary lining stress and displacement,discussed the deep buried reasonable diversion tunnel secondary lining time,finally given the secondary support time of the Yunnan water diversion engineering in Luzhi river.