Zoning of mutual influence of approach rock tunnels based on a safety factor

For multiple approach tunnels, the construction of the new tunnel near the existing tunnel modifies the state of stresses and movements around the existing tunnel in an area called the “influence zone”. In this study, new method is developed to optimize the relative position of approach tunnels and guide their design via the zoning of mutual influence of the approach tunnels based on a safety factor. The strength reduction method is applied to calculate the global safety factor of multiple approach tunnels in limit state. According to quantitative laws of variation in the safety factor from single tunnel to multiple tunnels, the strong influence, weak influence, and no influence have been zoning to guide the design and construction of approach tunnels. By changing the relative position of the new tunnel complex, the safety factor and failure shapes of the tunnel complex in several cases are obtained through numerical simulation. The results are based on dividing the influence zone of approach construction of the new tunnel complex. Combining the influence zone with failure shapes, the relative position of the tunnel complex is optimized. Special support countermeasures for weak tunnel complex parts and parameters of support are initially determined.