Contemporary Supports in Squeezing Rock and a Possible Alternative Method

Abstract

Challenges of the support for tunnelling in squeezing ground are still common and have yet to be completely resolved. In this paper, contemporary supports are introduced and 3 critical problems for future support methods through squeezing ground are summarized. With the continuous development of tunnel construction equipment, based on the perspective of preserving and exerting the self-bearing capacity of surrounding rock, an innovative clue of tunnel support, pre-structuralized method, is put forward. The proposed method with a different construction sequence stacking up against the existing support evolved from traditional advanced pre-support. Pre-structure should be formed along with tunnel profile before excavation at the tunnelling face. On the one hand, it could effectively control the deformation of surrounding rock in front of the excavating face; on the other hand, the pre-structure can ensure the surrounding rock under triaxial compression from beginning to end to boost its strength. There be two possible technical routes to achieve a pre-structure in this preliminary study. One is to construct lining in advance of excavating, the other is to reinforce the surrounding rock in advance to form a pre-reinforcement hollow. Based on the numerical simulation, considering the rheological effect of squeezing rock, the deformation control effect of the pre-structure method is studied. Firstly, the numerical model is verified and calibrated by the analytical solution of an unsupported circular opening. Then, the comparative analysis of the deformation control effects of the traditional support, the pre-lining in advance, and the pre-reinforcement hollow in advance is carried out, respectively. The results show that: 1. Compared with the traditional support, the pre-structuralized method can effectively preserve the surrounding rock after excavation. The plastic zone and deformation convergence of surrounding rock of the latter are much smaller than that of the traditional one; 2. As for the pre-structuralized method, compared with the pre-reinforcement hollow in advance, the deformation control effect of the pre-lining in advance is better, but the internal force of the latter has exceeded the design value. Further considering the stability of lining in the actual construction process, the pre-lining in advance is not a preferable scheme, which needs further study. In contrast, the pre-reinforcement hollow in advance can reduce the deformation by improving the physical and mechanical properties, and self-bearing capacity of surrounding rock, which is the future direction of support.