Project Description:

 Infinitus Public Square project pit is surrounded by roads, and subway line 2 is underneath in the middle of the east and west plots pit. The east side of the east plot is adjacent to the Bijieyuan project, under which there is a 3-storey basement, and the side adjacent to this project adopts the support form of large slope excavation, and the environment around the foundation pit is complicated. According to the design drawings, the safety level of the pit design of this project is Grade 1. The middle part of the two sides of the pit adjacent to the subway is supported by double-row piles + tensile strands, the four corners are supported by supporting piles + corner braces, the outer side is supported by φ850@600 triaxial mixing piles to form a water-stopping curtain, with the depth going down to the surface of the gray rock, and the rest of the section is supported by the supporting piles + expanding head of the prestressing anchors (or ordinary prestressing anchors) support scheme.

 The monitoring program includes: pit monitoring (horizontal displacement of the top of the enclosure structure, vertical displacement of the top of the enclosure structure, deep horizontal displacement of the enclosure structure, axial force of the support, groundwater level, settlement of buildings (structures) around the pit, settlement of the subway entrances and exits, etc.), automatic monitoring of structural deformation of the subway tunnels (monitoring of the horizontal displacement, vertical displacement), monitoring of the highly supported molds (settlement of the moldboards, horizontal displacement of the supports, inclination of vertical rods, (formwork settlement, horizontal displacement of support, inclination angle of vertical rod, axial force of vertical rod), subway entrance and exit monitoring and structural deformation monitoring of Hangyun Power Tunnel.

 The structural stability of the deep foundation pit itself is the focus of monitoring in this project. In addition, due to the complex environment around the foundation pit, there are under-construction Cinnamon Garden project, Hangyun Power Tunnel, Metro Line 2 Tunnel and many underground pipelines, and there is a cavern at the bottom of the Metro Tunnel with a height of more than 13m, so the impact of the construction on the surrounding environment, the water table, and the structural displacement of the neighboring Metro structure are also the focus of the monitoring.

Technical Highlights:

 1. Early warning was given many times during the construction process to ensure the safety of the pit and the operating subway.

 2. Grouting on both sides and at the bottom of the operating subway to lift and reinforce the operating subway tunnel structure, with good implementation effect.

 3. The independently researched and developed application platform for automatic monitoring of structural deformation of urban rail transit was adopted, realizing 24-hour uninterrupted automatic monitoring.

 4. A push-scan laser scanning system (GRP5000 type) was applied in this project to store the changes in the health status of the tunnel structure in time and space.

 5. The joint application of multi-sensors provides the basis for the project to timely and accurately obtain the displacement change rules of the pit enclosure structure and the subway tunnel structure during the construction period, which provides a guarantee for the health of the subway structure and the safety of the operation.