双洞八车道特大跨度隧道Ⅴ级石质围岩开挖工法

Excavation Method forⅤ-Grade Surrounding Rock of Double-Hole Eight-Lane Super-Long-Span Tunnel

为减小双洞八车道特大跨度隧道洞口Ⅴ级石质围岩后行导坑爆破对已完成支护结构的不利影响,该文以平潭牛寨山隧道工程为例,针对原设计双侧壁导坑法在后行的临近导坑爆破时,易将原先已施工完成的临时钢支撑震塌,提出取消临时横向支撑的变更方案1,以及带竖向支撑的上下台阶法(变更方案2),再利用有限元法计算,模拟3种不同开挖工法对隧道变形及受力的影响。计算结果表明:3种方案引起的拱顶沉降相差较小,最大相差约11.8%;变更方案2引起的围岩应力最大,但变更方案2同时取消了左右侧壁导坑的横向支撑以及左右侧壁导坑下台阶的竖向支撑,大大简化了施工工序。最后,结合监测数据进行分析,隧道结构安全稳定,变更方案2不仅合理可靠,而且加快了施工进度,节约了造价。

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 withⅤ-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.