Finite Element Analysis on Double-Layer Pipe Roof Pre-Support Effect of Tunnel in Shallow Buried Soft Stratum

Pipe roof methods are frequently used in tunnel construction. The pre-support method of double-layer pipe roof is one form of pipe roof method. In this paper, combining the project instance, the comparative analysis was completed. Single- and double-layer pipe roof pre-support is used in the design scheme of a large-span micro-arched tunnel in shallow buried soft stratum. First, according to results of excavation monitoring, using back analysis method, the parameters of surrounding rock were defined. Second, the FEA model was established. Using this model the arch subsidence and internal force of initial support and temporary support under three different support forms including single-layer pipe roof form, double-layer pipe roof form, and no pipe roof support form were calculated. The calculation results indicated relative to no pipe roof support, the application of single-layer pipe roof support will significantly reduce internal force of initial support and surrounding rock deformation. And compared with the single-layer pipe roof support, the double-layer ones don't have preferable support effect.