The Gongbei Pipe Arch Tunnel is not only the world's largest tunnel built with the pipe arch method, but also part of the longest bridge building project ever: the Hong Kong-Zhuhai-Macau Bridge. As a section of the western link to the 50 kilometer long gigantic infrastructure project across the Pearl River Delta, a few meters from the coast the tunnel runs under the busy border crossing between Macau and Zhuhai. With three lanes in each direction the direct road link between the two economic centers of Hong Kong and Macau means an immense reduction in the travel distance and journey times.
For the realization of the gigantic project four Herrenknecht AVN Machines were used. In July 2013 boring of the first of a total of 36 holes along the planned tunnel cross section took place. The small diameter machines generally took 15-20 days for the 255 meter long distances. By late August 2013 the other machines gradually began their tunnelling operations. Most of the time all the machines were in use simultaneously and working in opposite directions. One Herrenknecht separation plant was connected to each pair of machines.
A special challenge was the precision required at distances of only 350 millimeters between each hole. A critical success factor for the Gongbei pipe arch was therefore equipping the AVN Machines with the SLS Microtunnelling navigation system from VMT. Lining of the tunnels using pipe jacking was thus done with millimeter precision, and in the deeper boreholes even at water pressures of up to 2.7 bar. The last of the numerous breakthroughs by the endurance borers took place in May 2015. Then in a second step the subsoil was frozen and finally the actual tunnel excavated and secured using conventional mining methods under the protection of the pipe arch. The way to the almost 30 kilometer long world's longest bridge was clear!