Stability Research On The Large Cross-section Tunnel In Weak Rock

In tunnel excavation can cause a great disturbance to the rock mass in the proces, poorly controlled it will cause a serious hazard, especially in the poor geological conditions of large cross section tunnel surroundingrock instability is widespread. With the increasing level highway and weak rock more generally, how to ensure that under conditions of poor geological conditions, safe and fast construction, has become a difficult academic research.Taking a tunnel project as the background, using the theoretical analysis, numerical simulation and field monitor measuring combining weak surrounding rock stability of large cross-section of the tunnel structure were studied. The main contents include:The factors affecting the stability of large cross-section tunnel in weak rock is analyzed. To selection typical section, qualitative analysis of the stability of surrounding rock. Numerical simulation on three step method and CD method, form displacement and stress and structure aspects of such comparative research, in order to select the optimal construction method. Field monitoring data were analyzed and compared with the numerical results, summed up the tunnel surrounding rock deformation, and to assess the security of primary support and secondary lining for a reasonable time, guide the construction.Through the research of the main results obtained are as follows:1) According to the existing research results at home and abroad, summed up the large cross-section tunnel in weak rock mechanics characteristics and the main factors affecting the stability of surrounding rock, the basic criterion of surrounding rock instability are obtained.2) From the development degree of rock mass strength and the structural planes of rock mass, the tunnel surrounding rock between poor stability and instability.3) Using the three-dimensional numerical simulation analysis of three-step method and CD method, the analysis results show that three-step method and CD method can satisfy the safety of the engineering construction, and the CD method is better than three steps method. Considering the two kinds of method of construction project cost, construction safety and so on, suggested that the three step method is used for the tunnel construction.4) From the point of monitoring results, the tunnel initial structure and measures on the safe side, the second lining for settlement of vault is 96%, has around 93% of convergence. Based on the principle of deformation rate, the results show that 29～31d after excavation is the optimal supporting time.5) The numerical simulation results and monitoring measurement results contrast analysis and validation, find the tendency is roughly same, shows that the simulation results more reliable.