浅埋红层软弱隧道围岩破坏特性模型试验研究

软弱隧道围岩浅埋段在施工时极易出现较大变形和塌方破坏事故,已成为隧道工程施工中的难点。依托广(通)—大(理)铁路南华1号隧道工程项目,通过模型试验对滇中典型红层软弱隧道围岩的变性破坏模式及应力扰动特征进行了研究。研究结果表明:隧道开挖容易引起两侧拱腰处岩体与水平方向夹角成45°+?/2的区域内开始出现初始裂缝,并向上延伸至拱顶最终形成高度约为0.5倍洞径的塌落拱;隧道开挖将引起围岩应力重分布,在隧道周边形成一圈应力降低区,在其外侧是应力升高区,而岩体塌落区则位于应力降低区内;为减少围岩塌落破坏风险,一方面应尽早支护成环,另一方面宜对应力降低区岩体进行适当加固,并充分利用岩体的自承载能力。上述研究成果不仅可用于指导本工程的设计与施工,而且也可为今后类似工程提供借鉴和参考。

Model tests on failure characteristics of red weak surrounding rock of shallow buried tunnels

During the construction of shallow buried tunnel with weak surrounding rock mass, large deformation and landslide accident are likely to occur, which has become one of the difficult problems for tunnel construction. The model tests are performed to study the deformation failure modes as well as the stress disturbance characteristics of red weak surrounding rock of Nanhua No.1 Tunnel project of Guangtong-Dali Railway. The results show that there are cracks with an angle of 45°+φ/2 to the horizontal plane at both sides of the tunnel waist after tunnel excavation, and these initial cracks gradually extend upwards to the crown, eventually forming a collapse arch with a height of approximately 0.5 times the tunnel diameter. Moreover, the tunnel excavation will cause the stress redistribution of surrounding rock stress, forming a circle of stress-reducing zone around the tunnel, and at the outside is the stress increase zone, while the rock mass collapse area is mainly located in the stress-reducing zone. In order to reduce the collapse risk, on the one hand, the exposed surrounding rock should be supported as one whole ring as soon as possible. On the other hand, the rock mass in the stress-reducing zone should be appropriately reinforced to make full use of its self-supporting capacity. These findings can be used to guide the design and construction of this project and may provide reference for future similar projects.