Abstract:

In order to solve the serious deformation crack of primary support （247 m of excavated section） of Zhongtiaoshan Tunnel when encountering F7 main fault with high ground stress, two schemes, i.e. one time rigid support and stress release by flexible and secondary support, are carried out for different test sections; and then the monitoring data are analyzed and the primary support appearance is observed. Some conclusions are drawn as follows: (1) The deformation velocity of large deformation soft rock section by one time rigid support is much lower than that by flexible support; the maximum convergence velocity is reduced from 28 mm/d to 18 mm/d, and the maximum settlement velocity is reduced from 24 mm/d to 12.8 mm/d; and the deformation is much easier to control after stress release. (2) The primary support deformation crack can be effectively controlled, the tunnel structure quality can be guaranteed, and the successful passing through F7 main fault can be realized by adopting one time rigid support supplemented by optimized tunnel sidewall curvature and other construction methods.

Key words: Menghua Railway, Zhongtiaoshan Tunnel, F7 main fault, high ground stress, large deformation of soft rock, rigid support, flexible support, primary support crack