Abstract:

When the stability of an opencut tunnel portal close to the antislide piles of the subgrade is calculated based on the band theory, the calculation result is often too conservative. In the paper, static analysis is made on an opencut portal of a singletrack railway tunnel under active earth pressure by means of ANSYS program, and a new stability analysis method, which is different from the conventional band theory, is proposed. The main research contents and conclusions are as follows: 1) If, outside of the tunnel portal structure, there are piles which constrain the deformation of the tunnel portal, the result of the conventional band theory is too conservative; in such case, integral stability analysis can be made based on the whole force system, which may result in the reduction of the amount and construction difficulty of masonry works and the improvement of the economic rationality of the design, while the same safety coefficient is satisfied; 2) When the tunnel portal structure is close to the piles and the clear spacing between the piles and the tunnel portal is less than 3 times the pile diameter, the piles have obvious effect in improving the stability of the tunnel portal; as the clear spacing between the piles and the tunnel portal increases, the safety coefficient reduces; when the clear spacing between the piles and the tunnel portal is 3～4 times the pile diameter, the safety coefficient cannot meet the requirements of relevant codes.

Key words: tunnel, opencut portal, antislide pile, integral stability analysis, clear spacing between pile and tunnel portal