浅埋大跨小净距隧道安全净距与中岩柱力学特性研究

Study on safe clear distance and mechanical characteristics of middle rock pillar for shallow large-span tunnel with small clear distance

结合魁歧双洞八车道小净距隧道工程实践,采用三维弹塑性有限元,通过分析围岩位移、等效塑性应变以及隧道安全系数随净距的变化,综合确定魁歧隧道最小净距为0.55B是安全、合适的。在隧道开挖模拟过程中,采用三种不同中间岩柱加固措施,研究Ⅲ、Ⅳ、Ⅴ级围岩条件下中间岩柱受力、变形特性。研究结果表明,预应力锚杆对控制围岩水平变形最为有效,软弱围岩小导管注浆加固效果较好,高级别围岩宜采取预应力锚杆加固。研究结论可为类似条件下特大断面小净距隧道的设计、开挖、岩墙加固提供理论依据,对工程实践具有指导意义。

According to the construction of Kuiqi tunnel which is with two bores and eight lanes and with super-large section and span,the 3D elastoplastic FEM is used to analyze the variation of the surrounding rock displacement,the equivalent plastic strain and the safety factors with different clear distances.The safe clear distance of the large-span tunnels with small clear distance is determined as 0.55B,which is safe and appropriate.In the process of the tunnel excavation simulation,three kinds of middle rock pillar reinforcement measures are used,and the force and deformation characteristics of the middle rock pillar under the surrounding rock with level Ⅲ、 Ⅳ and Ⅴ are studied.The study results show that the prestressed anchors are the most effective for the horizontal deformation control of the surrounding rock and the grouting with small pipe is quite effective for weak surrounding rock.The results could provide the scientific basis to the design,excavation method and dike strengthening of the large-span tunnel with small clear distance.