Stability analysis of two parallel closely spaced tunnels based on convergence-confinement principle

Stability analysis and risk assessment are key issues in the design and construction of tunnels; however, these assessments are often hard to conduct accurately because of the complexity of tunnel engineering. In order to improve tunnel construction technology, this paper uses the safety factor as the assessment index. A quantitative analysis method for tunnels is presented by using the convergence-confinement principle and the numerical simulation analysis method. To meet these objectives, based on the actual construction technology, the tunneling method is studied using a detailed numerical model to investigate the effects of different patterns for advancing the tunnel face. A new method for solving the safety factor of the support structure is proposed using a three-dimensional numerical model; the detailed solution process is illustrated through the case of Luoyixi tunnel. The results show that the safety factor of a lagging tunnel is significantly less than that of the leading tunnel, and that in order to ensure the stability of a lagging tunnel, reinforcement measures should be included during the construction process. Moreover, there is also a danger signal for leading tunnels: the direction of the butterfly-shaped wings in the plastic zone began to deflect to the vault at the start of lagging tunnel construction. In order to prevent the possibility of the roof falling, an advanced rockbolt should be applied in time. For designers and builders, the developed quantitative method in the form of safety factors can be used for a comprehensive evaluation of the support design and the rock state. For these reasons, this method is a convenient option for optimization analysis in construction technology.