| Abstract:This paper carried out the adaptability of different excavation methods at accumulation body shallow tunnel through analysis the large deformation at starting excavation and collapse accidents and later treatment scheme and implementation effect, combined with engineering practice of Shan shuao tunnel. This paper offers technical support and experience for similar weak surrounding rock tunnel and the main research contents include:1. Based on the security risk assessment of Shan shuao tunnel at construction stage, security risk level was judged as grade Ⅱ (medium risk) while the security risk level of entrance instability and collapse accidents at accumulation body shallow section. There should formulate risk mitigation measures to ensure the safety of construction.2. Through, the comparison of two different methods, the adaptive numerical results shows that the three-step method with seven steps are more conducive to control the deformation of surrounding rock than CD method at faultage accumulation shallow stratum.3. Three-step method with seven steps is easy to happen arch drop or large deformation or collapse accidents at application of class VI weak rock. At different steps in the conversion process by steps, internal force and deformation will increase with the work process of top step and medium step. Because CD method added temporary vertical supports, internal force and deformation of each construction process by steps reduced significantly compared with three-step method with seven steps. This was in favor of the stability of supporting structure system in shallow sections of tunnel.4. This paper summarized the reasons for collapse at faultage accumulation shallow stratum and construction technology and management points of CD method. The construction of100m long entrance section of loose accumulation shallow was completed successfully and it provided the experience and references for similar projects. |
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