Research on Mechanical Characteristic of Weak Surrounding Rock Large Span Double and Multi-Arch Tunnel Construction

According to construction scheme of some weak surrounding rock large span double and multi-arch tunnel works, finite element value simulation method is adopted to research weak surrounding rock deformation characteristic, anchor bolt mechanics characteristic, preliminary support and secondary lining structure mechanical characteristics, etc, and the research result shows that: repeatedly disturbance of excavation of middle pilot tunnel and subsequent supporting excavation shall easily reduce surrounding rock strength in the range of middle wall top and middle line of arch top of left and right pilot tunnels, therefore, prior to excavation of middle pilot tunnel, surrounding rock of tunnel top shall be pregrouting reinforced to improve integrated strength of surrounding rock of arch top, max. Accumulated settlement displacement of tunnel is 19.45 mm, max. Horizontal convergence displacement of side wall of left and right tunnel is 9.71 mm, max. Vertical upheaval displacement of middle wall bottom is 8.82 mm, above displacement can all be within controlled range satisfying design requirement; max. plastic zone vertical depth of upper side of left and right tunnel arch top is respectively 1.23 m and 2.06 m, inverted arch bottom plastic zone vertical depth is 2.74 m and 3.37 m, radial depth of middle plastic zone of side wall of left and right tunnel is respectively 0.87 m and 1.73 m, mutual impact range of spatial effect of tunnel face of left and right tunnel is 3 folds tunnel span. This research shall be referred to by similar Tunnel design and construction.