| When a tunnel crosses a fractured and loose rock stratum rich in joints,the excavation and unloading will cause the structural surface of the surrounding rock to open up and the strength and stability to decrease accordingly,which will easily lead to tunnel collapse accidents.In this paper,the modeling method and construction optimization of tunnels through fractured rock formations are studied by means of field acquisition,experimental testing,numerical analysis and field monitoring based on actual projects,and the main work and results are as follows.(1)The deformation and force characteristics of the tunnel through fractured and loose rock were analyzed and determined by using field acquisition and field testing,and the refined description of the tunnel joint development characteristics was reasonably carried out based on the field acquisition data to realize the accurate identification and refined numerical modeling of the structural surface of the fractured rock.(2)To address the limitations of continuous probabilistic model to simulate rock tunnels with fractured geological structure,a modeling and analysis method for fractured and loose rock tunnels is established,based on Monte-Carlo stochastic simulation method,random variables corresponding to the real distribution function are obtained according to the known probability distribution function,and these variables contain the length and yield of the structural surface,so as to generate a tunnel structural surface that can characterize The discrete fracture model is generated to characterize the structural surface of the tunnel.(3)The discrete element modeling method was used to conduct a multi-case numerical analysis of the tunnel excavation of fractured and loose rock,and the results obtained were in good agreement with the measured deformation,which verified the reliability of the calculation method and clarified the laws of surrounding rock deformation,support structure force and plastic zone distribution after excavation of fractured and loose rock under different construction methods,different feeds and different parameters of support measures,etc.,so as to optimize the proposal of the applicable The construction method and support measures for Jiao Wei Qin tunnel were optimized.(4)The field test and analysis of mechanical behavior of tunnel construction in jointed and fractured rock mass are carried out.The reliability of block discrete element model and the feasibility of optimization scheme are verified by means of surrounding rock displacement and steel arch support stress monitoring,loose circle test and other methods,which can provide reference for similar engineering optimization. |
