Abstract: The aim of this research is to obtain the stability and explore the reinforcement scheme for the middle rock column of the Baizhushan No.1 Tunnel with small clear spacing in Deyang,Sichuan.On the basis of Protodyakonov's equilibrium arch theory,the formula of the pressure of surrounding rock overlying the middle rock column is proposed,and factors affecting the surrounding rock pressure on the tunnel are analyzed.Furthermore,the displacement of surrounding rock,the distribution of plastic zone,and the vertical stress distribution of the middle rock column with varied spacing are examined by establishing a 3D finite element model using MIDAS GTS NX.The reasonable clear distance is determined.In addition,the middle rock column is partitioned for grouting reinforcement of different combinations to study the control effect of different reinforcement schemes on surrounding rock deformation.Results demonstrate that the formation of equilibrium arch and the pressure of overlying surrounding rock are directly affected by the excavation method of tunnel,the reinforcement method of the middle rock column,and the clear distance of tunnel.The designed clear distance 13.94 m at the entrance of Baizhushan No.1 tunnel is reasonable.Small pipe grouting reinforcement for the middle rock column and the rock tray has greatly enhanced the integrity and stability of the middle rock column and restrained the deformation of surrounding rock.

Key words: shallow-buried tunnel with small clear spacing, stability of middle rock column, reasonable clear distance, small pipe grouting, optimizing reinforcement method