Mechanical Behaviors of Existing Large-Diameter Tunnel Induced by Horseshoe-Shaped Undercrossing Twin Tunnels in Gravel

This article investigates and presents a case study on the Beijing Subway Line 12 excavation beneath existing Qinghuayuan Tunnel. The composite pre-reinforcement technique was used in conjunction with shallow tunneling method to control distortion of large-diameter tunnel. When building twin tunnels underneath, this strategy considerably decreased impact To systematically mechanical response tunnel, variety sensors embedded prefabricated segments just above new tunnels. During undercrossing procedure, earth pressure, tunnel crown settlement, opening width segment joint, circumferential strain were all measured. settlement development categorized under six stages: (1) sedimentation, (2) heave, (3) second (4) (5) third (6) steady state. joint changed sharply during pressure concrete stress linings rapidly increased majority reinforcement stresses compressive far lower than yield strength, indicating that safe working condition.