大断面软岩隧道三台阶开挖技术优化研究

Study on the Optimization of Three Step Excavation Technology of Large Section Soft Rock Tunnel

为了解决大断面软岩隧道的软弱破碎围岩径向位移增速快、开挖后初期支护结构不能尽早发挥作用、极大可能导致围岩失稳和发生安全事故等问题,以新奥法设计理念为基础,保证围岩自身一定的承载能力,同时满足围岩自身和支护结构的稳定性要求,初期支护施作适时而行。以马湾隧道为依托工程,对通过方案比选后得出的,仍存在诸多缺陷的三台阶分步交错开挖法进行优化改进,并借助有限元软件Midas/GTS建立隧道模型,对三台阶交错分步开挖法和优化改进后的三台阶同步开挖法进行数值模拟对比分析。最终确定优化改进后的三台阶同步开挖法:初支闭合较早,能有效减小围岩的变形;同时能够控制围岩塑性区的发展;初支轴力和弯矩略大于分步交错开挖法,但差距不大,不影响初支结构安全。经实际施工效果验证,三台阶同步开挖法施工优于三台阶分步交错开挖法,为大断面软岩隧道施工提供一种更安全的新方案。

In order to solve the problem that the radial displacement of the weak and broken surrounding rock of the large-section soft rock tunnel increases rapidly,the initial support structure cannot play a role as soon as possible after the excavation,which may cause the surrounding rock instability and safety accidents.Based on the design concept of the law,it guarantees a certain bearing capacity of the surrounding rock itself,and at the same time satisfies the stability requirements of the surrounding rock itself and the supporting structure,and the initial support construction is timely.Based on the Mawan Tunnel,the three-step staggered excavation method,which still has many defects,is optimized and improved after the comparison and selection of the schemes,and the tunnel model is established with the help of the finite element software Midas/GTS,and the three-step the staggered step-by-step excavation method and the optimized and improved three-step synchronous excavation method are compared and analyzed by numerical simulation.Finally,it is determined that the optimized and improved three-step synchronous excavation method,the initial support is closed earlier,can effectively reduce the deformation of the surrounding rock;at the same time,it can control the development of the plastic zone of the surrounding rock;the initial axial force and bending moment are slightly larger than the stepwise staggered excavation method,but the gap is small,and does not affect the safety of the initial support structure.Verified by actual construction results,the three-step simultaneous excavation method is better than the three-step stepwise staggered excavation method,which provides a safer new scheme for large-section soft rock tunnel construction.