Study on the Limit Value of Safety Overburden Layer Thickness of Large-Span Bias Tunnel

The number of mountain tunnels continues to increase, the explosive demand for traffic increases, and large-span bias tunnels are increasingly appearing in actual projects. Large-span biased tunnels can cause uneven lining stress, and unreasonable thickness of the soil can cause damage to the lining. This paper relies on the Beijing-Hong Kong-Macao Expressway Guangle Expressway. It adopts three construction methods, namely, double-wall method, three-step method and CRD method. At the same time, based on different soil thickness research, it is considered in 1:1, 1:2, 1: 3 Three kinds of slope effects, through the analysis of finite element numerical simulation results, the thickness limits of large-span bias tunnels under different slopes are given. The results show that the tunnel lining is under pressure within the thickness limit of the overburden. If it is too thin, it will cause the lining to be pulled and affect the stability of the tunnel. If it is too thick, it will increase the construction cost and waste. Therefore, the research on the thickness limit of large-span biased soil has a great guiding significance for design and construction.