Study On Construction Process Optimization Of Ultra-large Section Tunnel With Soft And Fractured Surrounding Rock And Its Application

As the development of China high-speed railway and passenger line construction, there have been a large number of tunnels with ultra-large section. The excavation cross-section area of these tunnels can be 150m2 or more. Especially for the soft and weak broken surrounding rock, the construction of these tunnels is very difficult. Although using traditional digging methods, for example, CD method, CRD method, double sides heading method, three benches and seven steps method, tunnels can be build safely, these methods of multi-segment will inevitably lead to slow construction schedule and low economic efficiency. Therefore, it is necessary to study the law of construction mechanics effects in ultra-large section tunnels with the soft and weak broken surrounding rock, for the optimization of a sort of fast safe and economical construction method. This can provide some experience of the future design and construction of such tunnels.In this thesis, with the means of laboratory rock sample test, numerical simulation, large-scale three dimensional geomechanical model test, and the support engineering of Liangshui Tunnel of Lanyu Railway, tunnel construction process optimization is studied around the ultra-large section tunnels with the soft and weak broken surrounding rock.Through laboratory mechanical tests of field carbonaceous phyllite, the rock's basic mechanical parameters, creep model and creep parameters are gotten. According to the mechanical test results and the field feedback data, numerical simulation is carried out in the ultra-large section tunnels with the soft and weak broken surrounding rock. Universal law of tunnel construction process mechanics effects is studied in this type tunnel. Numerical simulation can arrived at tunnel surrounding rock's mechanical effects in different formation conditions, excavation cycle footage, and excavation method. Similar material of carbonaceous phyllite, model test equipment system and multi-information gathering system are developed to carry out large-scale three-dimensional geomechanical model test. In this model test, there are studies on tunnel excavation process mechanical effects of bench method with support, whole section method with support, and whole section without support. Surrounding rock's mechanical effects are further analyzed in different excavation methods and support conditions. Through the comprehensive analysis of numerical simulation and model test conclusions, construction plan, two benches adding invert method, is proposed for Liangshui Tunnel test section. The feasibility of this plan is validated by comparing the on-site monitoring information with model test conclusions. According to the creep model and parameters, tunnel's long-term stability is verified by numerical analysis. The results show that the construction optimized is feasible. With this excavation method, construction efficiency of Liangshui Tunnel is raised, and the tunnel's long-term stability can be guaranteed.