Abstract: This paper presents the case history of Wengkai Expressway Siping Tunnel. The reinforcement measures of the central rock pillar were simulated by numerical simulation software. The deformation and mechanical characteristics of the middle rock pillar under different strengthening parameters were compared, and a grouting construction design option for the central rock pillar was proposed. The results show that when only the tension bolt is applied, the plastic zone of the central rock pillar is connected, and the maximum vertical settlement of the confining pressure is 10.1 mm. When the central rock pillar is grouted at the same time, the plastic zone can be effectively reduced, and when the surrounding rock parameters of the grouting strengthening area are increased by 50%, the plastic zone will no longer be connected. After grouting strengthening measures are taken, the settlement value of the arch top is controlled within one cm, and the construction safety is improved. The bending moment at the connection part of the steps is relatively large, and the initial support strengthening measures should be appropriately taken to ensure the stability of the support during the construction stage.

Key words: Tunnels；Small clearance, Central Rock Pillar, Grouting Strengthening, Stability Analysis