Field tests on large deformation control measures of surrounding rock of deep tunnels in fault zones with high geostress

The surrounding rock at the western piedmont of Yulong Snow Mountain fault zone of Zhongyi pilot tunnel at the tunnel exit of the Lijiang-Xianggelila railway is weak and fractured affected by the high geostress and fault zone, and the large deformation of the side wall is prominent. Four kinds of large deformation control measures for the surrounding rock are taken out in the field tests. The results show that the deformation of the surrounding rock is out of control adopting the general strengthening support measures (working condition 1). It needs slow release adopting control measures of resisting and reducing the stress of the surrounding rock. The stress of the surrounding rock of the test section is better controlled by working condition 3 (double-layer support + lower bench and inverted arch excavation), but the process is tedious and the construction progress is slow. Adopting the "strong support" measure of working condition 4 (monolayer support + strengthening arch support + reserved emergency reinforcement measures), the maximum daily rate of deformation and the maximum accumulation of deformation are the minimum, 3.2 cm/d and 62.2 cm respectively, the accumulation of deformation of the full test section is within the controllable range, the construction procedure is relatively simple, and the advance progress of the construction month can reach more than 90 m. In view of the advance effect of the pilot, It's highly recommended that the western piedmont of Yulong Snow Mountain fault zone of Zhongyi tunnel exit should adopt the working condition 4. The research results can provide a reference for large deformation control measures for the surrounding rock of deep tunnels in fault zones with high geostress.