Gongbei Port Tunnel Excavation Support Design and Construction
The Gongbei Port tunnel is a critical component of the Hong Kong-Zhuhai-Macau Bridge, currently the largest ongoing construction project in China, connecanwith a series of bridges and tunnels. It is a double deck, three-lane in each direction roadway tunnel with a length of 255 m, cross-sectional area of 345 m and approximate alignment curvature of 900 m. The tunnel is buried within soft sandy/silty clay about 4- to 5-m below the ground surface at Gongbei Customer Port. The poor ground condition, shallow burial depth, large opening area, small alignment curvature, and political sensitivity of the construction site leave the Gongbei Port tunnel to be the most engineering challenging task in the Hong Kong-Zhuhai-Macau Bridge project. This paper presents the design, construction organization and field pipe jacking tests of Gongbei Port tunnel excavation. The tunnel is designed to be excavated using conventional methods with a pipe roof in combination with in-pipe artificial ground freezing as excavation support. The pipe roof consists of 36 pieces of 1620-mm-diameter steel pipes jacked by slurry shield machines. The freez-ing pipes are installed inside roof pipes. Detailed construction organization plan related to the pipe jacking and ground freezing was discussed in the paper. Three dimensional numerical simulations were performed to verify the stability of the excavation. To control the project risk, two field pipe jacking tests were performed and the instrumentation data are analyzed. The Gongbei Port tunnel construction provides valuable case history experience for large underground excavation using conventional tunneling methods.