Abstract:

In view of the failure phenomenon of the primary support with small deformation in the rockburst section of Duanjiaping Tunnel on Menghua Railway, the rock strength around the tunnel, the geological conditions ahead of tunnel face and the initial geostress state are revealed by laboratory test, advance geological prediction, geostress test and other technical means; and the deformation and failure characteristics of the primary support are summarized and the causes are analyzed. It is concluded that the characteristics of surrounding rock, geological structure and construction method are the important factors affecting the deformation and failure of the primary support, and the local horizontal high geostress is the main cause. The deformation and failure of the primary support can be effectively controlled by technical measures, including strengthening the support parameters, adding buffer layer, adopting bolt and reinforced floor, adding damper, etc. The results show that: (1) The twobench method should be selected preferentially for excavation when the vertical joints are developed in surrounding rock of tunnel body under high initial geostress condition, which is dominated by horizontal tectonic stress. (2) The failure mode of the primary support concrete of arch and inverted arch is shear compression failure， and the main reinforcement failure mode of grid steel frame is eccentric buckling. (3) According to the characteristics of surrounding rock, supporting principle and field practice, corresponding technical measures should be adopted in case of high initial geostress, which is mainly composed of horizontal tectonic stress.

Key words: tunnel, high geostress, rockburst, primary support, deformation characteristic, deformation control, support parameter, buffer layer, bolt and reinforced floor, damper