The Study on the Threshold of Cover Depth of Large Section Loess Tunnel

Abstract

The method of load calculation in a tunnel is adopted by the state of covering depth. Due to the characteristics with macropore in loess stratum, the existing demarcation regulations of deep and shallow tunnels are inappropriate for the large section and shallow loess in highway tunnels. To determine the load of large section loess tunnel and provide a proper reference for structural design, the theoretical basis for distinguishing depth of deep and shallow tunnels as well as the characteristics of common calculation methods of surrounding rock load on depth are analysed. In this paper, a method distinguishing the threshold of cover depth of deep and shallow tunnels by coefficient of lateral pressure at the centre line of vault is put forward, in which the calculated results are consistent with the on-site findings. It can be concluded that the surrounding rock pressure in a deep tunnel is deformation pressure, while the surrounding rock pressure in a shallow tunnel is loosening pressure.