1. Key Laboratory of Urban Underground Engineering of the Ministry of Education, Beijing Jiaotong University, Beijing 100044, China
2. Subway Operation Technology Centre, Beijing Mass Transit Railway Operation Co., Ltd., Beijing 102208, China
3. Beijing Municipal Engineering Research Institute, Beijing 100037, China
Abstract：Based on the inspection results of some metro tunnels in Beijing, the influences of structural form, steel bar and service time on the defects of metro tunnels were investigated. The research results indicate that the defects of shield tunnel such as ovalization of cross section, lining cracks, dislocation of duct pieces and water leakage are mainly attributed to the deformation of segment joints. Lining crack was the main defect form in mining tunnel, and the width and depth of cracks with the discrete and random characteristics are influenced greatly by the service time of tunnel. Steel bar in concrete lining has a positive effect on the tunnel safety. Water leakages in metro tunnel are influenced greatly by rainfall and they usually occur at the segment joints and bolt holes of shield tunnel or the construction joints, deformation joints and lining cracks of mining tunnel. Most of lining holes with the shape approximate to strip, square or oval are often located at the arch crown accompanying with lining cracking nearby. Carbonation depth of lining concrete is proportional to the service time. The carbonation depth and rate appear to be the most at ballast bed, the less at sidewall and the least at arch crown. Crack is the common defect at ballast bed, and the separation between ballast bed and tunnel is accompanied by the longitudinal torsion.
