China Daily (Canada) - - CHINA -

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.

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