Excavation Method forⅤ-Grade Surrounding Rock of Double-Hole Eight-Lane Super-Long-Span Tunnel
In order to reduce the adverse effect of back heading blasting on the completed supporting structure at the entrance of a double-hole eight-lane super-long-span tunnel with Ⅴ-grade surrounding rock,the Niuzhaishan tunnel project in Pingtan was taken as an example.The original design of the double-side heading method is easy to cause the collapse of the temporary steel support that has been completed when blasting happens near the back heading.In view of this,this paper put forward scheme 1 of canceling the temporary transverse support and the up-and-down step method with vertical support(scheme 2).It then used the finite element method to calculate and simulate the influence of three different excavation methods on the deformation and stress of the tunnel.The calculation results show that the difference in crown settlement caused by the three schemes is small,and the maximum difference is about 11.8%.The surrounding rock stress caused by the second scheme is the largest,but the second scheme cancels the lateral support of the left and right side heading and the vertical support of the lower steps of the left and right side heading,which greatly simplifies the construction process.Finally,according to the monitoring data,the tunnel structure is safe and stable.It can be seen that scheme 2 is not only reasonable and reliable but also speeds up the construction progress and saves the cost.
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