Abstract:

The problems encountered during construction of Huangshanshao Tunnel on LijiangShangrila Railway crossing underneath rockpile section, i.e. surface cracking, serious sidewall deformation of primary support, etc., are studied. The surface displacement is monitored by 6 clinometers on ground, and 3 sections are arranged in the tunnel to measure the surrounding rock pressure, steel frame internal force, secondary lining internal force, contact pressure between primary support and secondary lining, and anchor axial force. Based on the analysis of the internal and external forces acting on the rockpile section, the crosssection type of secondary lining is optimized according to the numerical results, and the thickness and reinforcement of secondary lining are further increased. The following measures are adopted to effectively control the deformation of the rockpile section that tunnel crosses: (1) using the drainage and interception measures at cracks of earthrock interface of surface rockfill; (2) increasing the type of primary supporting steel frame and the length of radial system bolt at sidewall of rockpile section; (3) increasing the curvature of tunnel sidewall contour and optimizing the tunnel secondary lining type to round concurrent type; (4) increasing the reserved deformation of tunnel to 30 cm; (5) reserving 50 cm reinforcement space for tunnel lining clearance; (6) setting advance support of tunnel arch with 42 small conduit. After adopting the above measures, the tunnel has successfully crossed the rockpile section. According to the monitoring results inside and outside the tunnel, the structure is within the safe and controllable range.

Key words: rockpile tunnel, surface cracking, primary support deformation, long system bolt, sidewall curvature, round secondary lining, reinforcement space