HIGH-TECH ENSURES SUCCESS
Building tunnels is nothing new for Chinese engineers, yet boring the longest underwater tunnel in the world requires years of detailed planning.
Wang Mengshu, a tunnel and railway expert at the Chinese Academy of Engineering, said the Bohai Sea Tunnel project has been discussed for more than two decades and involved more than 100 experts. Now, Wang said, the technology is sophisticated enough thanks to the successful construction of the 8-km Jiaozhou Bay Tunnel and the 9-km Xiamen Xiang’an Tunnel.
Jiaozhou Bay is about 75 meters deep, roughly the same depth as Bohai Bay, which means it is feasible to apply the drilling and blasting method to the planned tunnel’s construction.
Drill and blast excavation entails drilling a number of holes into the rock and filling them with explosives, which are then detonated. The process is gradually repeated.
The drill and blast method is mainly for digging in hard rock.
Digging through soft seabed will need a tunnel shielding method, according to Wang.
A tunnel shielding method uses a support structure of concrete, cast iron or steel to protect the tunnel and the tunnel boring machines, which swirl blades (or the shield) about half the size of a basketball court to cut through the soft seabed.
Four vertical shafts will be drilled in the Bohai Bay region — in Penglai, Changshan and Huangcheng islands in Shandong province, and Laotieshan mountain in Liaoning province — to form the tunnel after the explosions.
Wang said two machines will drill through opposite sides of the sea floor until they meet in the middle. They can drill more than 600 meters a day, he explained, adding the project will be constructed by Chinese machines.