Analysis on excavation stability of tunnel portal with different design methods

The stability of tunnel portal has its particularity. Due to the influence of natural or human factors, it is easy to produce cracking, landslide, collapse and other diseases. Taking the No.5 highway tunnel of F3 bid in Georgia as the background, using the finite element analysis software MIDAS-GTS to establish a three-dimensional model to simulate the tunnel construction process. The tunnel portal adopts two design schemes of micro pile wall support and bolt mesh shotcrete support. Through the analysis and comparison of the transverse and vertical displacement and stress field characteristics of surrounding rock caused by two schemes of tunnel excavation, the influence of tunnel excavation on the stability of tunnel portal is studied. The numerical results show that the maximum transverse and longitudinal displacements of surrounding rock are 3.55mm and 8.73mm respectively, and the maximum tensile stress is 1.91mpa. Compared with the micro pile wall support design, the bolt mesh shotcrete support scheme is more feasible. The conclusion has a certain guiding role for the construction of highway tunnels in mountain areas.

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