Research On The Stability And Control Of The Small Spacing Tunnel Under The Drilling And Blasting Construction

With the rapid development of transportation infrastructure, railway double line tunnel, city double line tunnel and the tunnel excavation projects near or intermediate the new tunnels continue to emerge, there are many small spacing tunnel emerging. At present, due to the environmental characteristics of mountain tunnel itself, drilling and blasting method is still the main construction method. In the small spacing tunnel blasting excavation construction process, blasting will inevitably cause great damage to the stability of adjacent tunnel surrounding rock and supporting structure. Therefore, research on adverse effects of blasting on small spacing tunnel surrounding rock and lining stability and how to control it become the key problem in tunnel engineering and blasting engineering.This paper applies the rock elastic-plastic mechanics theory to analyze the mechanism of small spacing tunnel. Then the blasting stress wave propagation equation and the motion equation of the side wall are deduced with the method for analysis of rock mechanics.Taking Toudaoxue small spacing tunnel in Beijing Huairou District as the engineering background, a large number of blasting monitoring data is collected and analyzed. The three-dimensional finite element model of actual project is established with the ANSYS finite element software, the dynamic response of the small spacing tunnel driving blasting load was analyzed by the method of transient dynamic analysis.The main results obtained are as follows:(1) By comparing of on-site monitoring data and numerical simulation results, the correctness of the finite element model of the parameters are verified. Then the displacement, velocity and stress of the preceding tunnel lining are obtained through the analysis of the dynamic response of the finite element model. It is found that the tunnel arch foots and discontinuities are easy to appear stress concentration. And the side wall of the preceding tunnel in the face of blasting and rock pillar are the weak parts of the small spacing tunnel under the blasting, which need to be monitored and protected carefully.(2) Reserving the soil of lower step of the preceding tunnel is valid to reduce the maximum vibration velocity, which is verified by the comparison and analysis of vibration velocity, tunnel lining displacement and dynamic response stress in different construction procedures. An excavation procedure of small spacing tunnel which is good to reduce the vibration is put forward.