GUANGZHOU, Oct. 13 (Xinhua) -- A framework tunnel beneath the Guiyang-Guangzhou and Nanning-Guangzhou high-speed railways in Foshan, south China's Guangdong Province, has been precisely completed, according to China Railway 25th Bureau Group Co., Ltd. on Tuesday. The breakthrough marks significant progress in ultra-high-risk under-railway construction, successfully overcoming the challenge of building closely beneath busy operational high-speed rail lines and accumulating valuable practical experience for similar projects in China.
The No. 11 framework tunnel, located in Dali Town, Foshan, is a key and difficult control project. Above it are double-track operational high-speed rail lines with dense and frequent train traffic, placing it in the high-risk operational line construction category. Safety control and settlement control standards are far higher than those for conventional municipal projects. The closest distance between the tunnel construction area and the bottom of the operational high-speed rail track is only 2.85 meters. Earth excavation can easily disturb the soil, causing slight deformation of the subgrade and track. The control precision for track and subgrade settlement must reach the millimeter level, leaving extremely little tolerance. Any construction deviation would directly threaten high-speed rail operation safety.
"The biggest challenge facing the project is millimeter-level settlement control, and coupled with the fact that we can only work during nighttime maintenance windows, every step of excavation and support allows no error," said Jia Xiaohui, technical head of the project of China Railway 25th Bureau. The construction site faces many constraints and is difficult to organize. Surrounding structures and underground pipelines are dense, working space is limited, and large machinery is difficult to deploy. Due to high-speed rail operation restrictions, core procedures such as excavation and support can only be carried out during brief nighttime maintenance windows, putting considerable pressure on process coordination, resource allocation and safety control.
To safeguard high-speed rail operation safety and prevent subgrade deformation and settlement risks, the project team, after multiple rounds of discussion and expert demonstration, adopted a combined support technology of pipe curtain plus steel frame and D-type temporary beam overhead protection. It deployed an automated monitoring system to conduct 24-hour monitoring of subgrade settlement and track displacement, dynamically optimized construction parameters, seized maintenance windows to coordinate human and machinery resources, and carried out excavation and support in an orderly manner. The No. 11 framework tunnel was smoothly completed, ensuring high-speed rail operation safety.
Upon completion, the project will open up the cross-railway passage of Hedong Central Road, facilitate travel for local residents, further improve the local transportation network, and enhance regional road traffic efficiency.
