Jumbo job on Cheung Ching tunnel

HIGHLY specialised tunnelling units known as jumbos are being used on the Cheung Ching Tunnel part of Route 3.

As the work progresses, the fully computerised twin-boom jumbos drill two holes simultaneously.

The holes are then filled with explosives which, when detonated, produce a ''muck pile'' of rubble that will be removed with a special front-end loader designed for tunnel use.

Depending on the quality of the rock, the French engineers from Dragages may choose to employ a stair-stepping method, in which one jumbo drills into a forward tunnel face, while another drills into a face located a few metres back.

Both the jumbos and the loaders used on the Cheung Ching job are from Tamrock, in Turku, Finland.