Foundation Force and Grouting Reinforcement of Central Separate Wall in Shallow Buried Multi-arch Tunnel

In order to study the foundation deformation characteristics of the central separate wall of a shallow-buried multi-arch tunnel and the foundation grouting reinforcement method, the MIDAS/GTS software was used for numerical simulation calculation and analysis based on a proposed expressway multi-arch tunnel in Yunnan Province. The research results show that: (1) When the surrounding rock is good and the buried depth is small, the pressure distribution at the base of the central separate wall gradually changes from the “saddle-shaped” distribution to the “bell-shaped” distribution along with the construction process. The maximum base pressure appears at the toe of the right wall after the lining of the advance tunnel is poured. The foundation of the central separate wall is generally uplifted; (2) When the surrounding rock is poor or the buried depth is large, the pressure distribution at the base of the central separate wall is in a “saddle-shaped” distribution. The maximum base pressure appears at the middle right after the second lining of the rear tunnel is poured. The foundation of the central separate wall is generally in a state of settlement. (3) Through numerical analysis, the required bearing capacity of the partition wall foundation of the multi-arch tunnel under different burial depths and geological conditions is obtained. Combined with the current code and previous research results, a calculation method for the foundation bearing capacity of the central separate wall before and after the rock foundation reinforcement is proposed. The research results can provide reference for the design and construction of multi-arch tunnels.