Stability Analysis And On-site Monitoring Of Taihe Hydraulic Tunnel Crossing Fault Fracture Zone During Construction

As China’s economy and society rapidly develop,infrastructure construction such as water conservancy and transportation is booming,and the construction of tunnels and underground engineering is increasing.However,construction disasters frequently occur in water tunnels built under adverse geological conditions,such as the fault fracture zone,posing huge engineering hazards and risks.These hazards can cause collapses,sudden water and mud bursts,and other engineering accidents that can result in significant losses to the construction.This paper takes the construction of the Taihe Tunnel in the second phase of the Liangshan Daqiao Reservoir Irrigation District in Sichuan Province as a case study.By crossing the F1 and F2 fault zones,this project provides an excellent engineering background for investigating the risk problems encountered in the construction of tunnels that cross the fault fracture zone.The study involved numerical simulation and on-site displacement monitoring.The main work and achievements of the study are as follows:(1)The study used field survey data and construction-revealed geological conditions to preliminarily determine the physical and mechanical parameter range of the numerical simulation model.The sensitivity analysis numerical test plan of the fault mechanical parameters was designed to obtain the sensitivity influence range of different physical and mechanical parameters of the fault.The sensitivity analysis showed that the elastic modulus,friction angle,and cohesive force of the fault surrounding rock are highly sensitive to the deformation of tunnel excavation.Therefore,when analyzing the deformation effect of the fault,it is necessary to reasonably select the physical and mechanical parameters of the fault surrounding rock,such as the elastic modulus,friction angle,and cohesive force.(2)Through pre-construction geological forecast and numerical simulation analysis,the spatiotemporal effect law of tunnel crossing the fault fracture zone during construction was studied.The analysis showed that the existence of the fault fracture zone causes the influence range of the spatial effect of the settlement of the tunnel arch and the horizontal convergence displacement to be reduced.As the distance from the fault shortens,the deformation rate of the surrounding rock of the tunnel increases significantly.Therefore,based on the characteristics of the changes in the monitoring displacement of the tunnel’s different sections,the situation of the fault in front of the tunnel can be inferred and forecasted.(3)Through numerical analysis of the stability of the Taihe Tunnel crossing faults in the second phase of the Daqiao Reservoir,the stability characteristics of the tunnel under different conditions of advanced support parameters of small conduits were studied.The effects of small conduit diameter,length,and grouting reinforcement range on the stability of the tunnel were analyzed;Taking into account comprehensive factors such as construction technology and economic benefits,a construction advance support plan for the Taihe Tunnel crossing the fault fracture zone section has been proposed.(4)The study analyzed the stability of the construction of the tunnel crossing the F1 and F2 fault zones and the stress and deformation characteristics of the support structure under the determined support parameters.Based on the characteristics of the distribution of the displacement of the surrounding rock of the tunnel,the range of plastic zones,and the stress and axial force changes of the support structure’s stress and anchor rods,a construction plan for the tunnel crossing the F1 and F2 fault zones was proposed.On-site monitoring measurements were carried out to track the construction and verify the rationality of the proposed support parameters and the spatial effect characteristics of the deformation of the surrounding rock of the tunnel crossing the fault fracture zone.The spatial effect characteristics of the deformation of the tunnel crossing the fault fracture zone provide ideas based on deformation monitoring analysis to predict the fault fracture zone.