Abstract:

Liangshui tunnel on LanzhouChongqing railway is located in soft rock of carbon phyllite. The rock has extrahigh ground stress, with the maximum horizontal principal stress ranging from 6.5 MPa to 11.3 MPa. In the early stage of the tunnel construction, serious deformation occurred to the primary support structure, which resulted in distorted and fractured steel arches, instability of the support structure and interference of the primary support structure into the lining clearance. Therefore, the distorted primary support structure had to be dismantled and even cracks occurred to the secondary lining at local positions. In the paper, doubleshell primary support experiment and doubleshell secondary lining experiment are made, so as to solve the abovementioned problems. In the experiments, the primary support deformation, the surrounding rock pressure, the contact pressure, the steel arch stress, the steel bar stress and the concrete stress are studied. Conclusions drawn are as follows: 1) The deformation of the doubleshell primary support is relatively small, the stress of the shotcrete, steel arches, secondary lining concrete and secondary lining steel bars have not exceeded the allowable stresses of these materials, and the doubleshell primary support works well; 2) Due to the adoption of the doubleshell primary support, the steel bar binding process can be reduced, no additional lining formwork jumbos are needed, the construction organization is more convenient, and construction efficiency is relatively high.

Key words: LanzhouChongqing railway, Liangshui tunnel, doubleshell primary support, doubleshell secondary lining, field experiment, extrahigh ground stress, soft rock