Rail transit

Since the 1980s, my country's urban rail transit construction has developed rapidly. People's demand for fast and convenient urban transportation has been increasing, making high-capacity, punctual, and fast urban rail transit a key focus and hot topic in national infrastructure construction. During the 12th Five-Year Plan period, the national investment in urban rail transit construction reached at least two trillion yuan. Cities with completed subway systems include Beijing, Tianjin, Shanghai, Guangzhou, and Nanjing. Meanwhile, cities such as Fuzhou, Qingdao, Changsha, Chongqing, Wuhan, Changchun, Shenyang, Dalian, Hangzhou, Chengdu, and Xi'an are actively applying for or have already begun construction on subways. Currently, Beijing's subway, which opened on October 1, 1969, has 14 lines with a total length of 339.5 km and 191 stations. Shanghai currently has 13 lines with a total length of 567 km, and is expected to reach 20 lines with 877 km by 2020. At the same time, structural deformation accidents during subway construction and operation are frequent in China. How to effectively monitor and actively prevent these accidents has become a crucial issue for subway operators to consider. A survey of several operational subway lines across the country revealed that deformation occurred in the main structures, including tunnels, viaducts, U-shaped structures, and roadbed retaining walls, during construction and operation. This deformation caused track settlement and, in severe cases, compromised the operational safety of the subway. Therefore, it is essential to monitor the deformation of subway structures in a timely manner and eliminate potential safety hazards. Based on the monitoring results, remedial measures should be proposed promptly to ensure the safe operation of the subway.

A real estate company in Wuhan plans to construct a new residential building in Wuhan. The excavation area for the foundation pit is 32,000 square meters, with a support perimeter of approximately 1200 meters and an excavation depth of approximately 8.04 meters to 10.80 meters. The project is divided into two plots, north and south. The south plot has a net distance of 12.07 meters from the outer surface of the tunnel section structure, encroaching on the rail transit safety protection line by 37.93 meters. The north plot has a net distance of 8.58 meters from the outer surface of the tunnel section structure, encroaching on the rail transit safety protection line by 41.42 meters. According to the "Technical Specification for Structural Monitoring During the Operation Period of Rail Transit Engineering," deformation monitoring of the subway tunnel section must be implemented during the construction of this project to provide the owner with timely and reliable data and information to assess the impact of the project construction on the existing subway structure and the surrounding environment. This monitoring must also provide timely and accurate forecasts of potential hazards or accidents that could endanger the safety of the subway and the surrounding environment, allowing all relevant parties time to react and prevent accidents from occurring.

The main impact area of ​​the foundation pit on the north plot of the proposed project on the rail transit tunnel is 250m, and the main impact area of ​​the foundation pit on the south plot of the proposed project on the rail transit tunnel is 152m. The area at the junction of the foundation pits on the north and south plots is 16m. The secondary impact area of ​​the north plot extends outward by 80m, and the secondary impact area of ​​the south plot extends outward by 50m. The monitoring range is approximately 548m.

Due to the large survey area, a single device could not meet the requirements of this project. Therefore, a multi-device joint monitoring approach was adopted for automated monitoring. This joint monitoring project unified all monitoring points under the same coordinate system, facilitating better data analysis and processing, and providing the management unit with a more accurate understanding of the deformation situation. Specifically, considering the characteristics of a tunnel in the Wuhan Metro, a single line employed four Trimble robotic total stations combined with an automated monitoring system. Through free station placement and continuous data transfer, fully automated monitoring was achieved through multi-station joint monitoring. Qimai Safety, with its excellent products and efficient, professional technical services, helped the client successfully complete the automated installation and implementation of this project, while also meeting the requirements of unified, real-time, efficient, and high-precision data for the metro tunnel.