关键词: 地铁盾构隧道, 暗挖隧道, 地下空间, 下穿上跨既有结构, 数值模拟, 监测分析, 变形控制

Abstract: The construction of structures underpassing and overpassing an existing metro shield tunnel disturbs the existing structure repetitively, resulting in large deformation and crack leakage. Therefore, to address these issues and design a rational deformation control scheme, a case study is conducted on the Gangxiabei comprehensive transportation hub project in Shenzhe, China. Prereinforcement, auxiliary engineering measures, and key technologies of excavation and support are adopted for the mined cable tunnel at the lower level, and the numerical simulation of different precipitation depths, longitudinal segment sequence length, and basement reinforcement schemes are adopted for the parallel upper span of the underground commercial space at the upper level. Through informatized monitoring, the influence patterns of engineering construction on the deformation of adjacent existing metro shield tunnel is explored and validated. The results reveal the following: (1) The mined cable tunnel is considerably affected by the disturbance within 20 m, and the pipe roof prereinforcement measures with a length over 20 m can be used to control the deformation. (2) The effective measures to reduce the deformation of the existing metro tunnel are to improve the stiffness of the arch frame of the cable tunnel and increase the number of footlocking anchors. (3) The prereinforcement grouting pressure should be controlled at 0.5 MPa, and the floating of the existing shield tunnel should be controlled within +2 mm. (4) The underground commercial space at the upper level is excavated in parallel to the existing metro shield, and the largearea unloading will cause a sudden change of floating deformation under the timespace effect. The length of the structural segment and the exposure time should be shortened. (5) The dewatering construction should be implemented step by step to reach the depth of the bottom of the existing metro shield tunnel, which can reasonably balance the consolidation settlement of soil caused by dewatering and the floating of tunnel caused by earthwork excavation. (6) The actual deformation of the existing metro shield tunnel caused by the parallel construction of the underground commercial space is more significant than that of the numerical simulation within the range of 30 m under the influence of the disturbance, and the influence on the deformation of the existing structure decreases with an increasing disturbance distance.

Key words: metro shield tunnel, mined tunnel, underground space, underpass and overpass existing structure, numerical simulation, monitoring analysis, deformation control