MORE THAN 1,500 piles are being bored by a fleet of 12 HD Engineering drill rigs for one of the most challenging parts of Hong Kong's East Rail Extension.
The extension will take the line 1km south of Hung Hom Station in Kowloon to the new East Tsim Sha Tsui underground terminus.
This has to be shoehorned into a cut-and-cover box between Salisbury Road, a multi-storey car park and the steep sided Signal Hill in a densely populated area with several luxury hotels.
Although it is short, the extension is vital for owner and operator the Kowloon Canton Railway Corporation because the new terminus will be another interchange with the Mass Transit Railway (MTR), reducing passenger congestion at the Kowloon Tong MTR interchange.
East Tsim Sha Tsui Station will also form part of the planned Kowloon southern loop that will connect the East and West Rail systems for the first time.
The complex extension project has been spilt into three sections.
Contractor Gammon Skanska is involved in all three, two in joint venture with Japanese tunnelling firm Nishimatsu Construction.
The jv has the HK$1561M (£131M) contract to build the East Tsim Sha Tsui station and the £29M contract to build 1km of pedestrian subways linking it with the MTR station.
Gammon Skanska also won the £54M contract to build the cutand-cover tunnels between Hung Hom and the new terminus, mainly along Salisbury Road. The new tunnels run above the busy Cross Harbour tunnel.
The fleet of HD rigs, including HD205Ps (HD Engineering's latest heavy duty rig), is drilling the holes for the piles for the station and the cut-and-cover tunnels. It is supported by a fleet of more than 30 Atlas Copco XRS415 and XRS870 compressors that supply compressed air power to down the hole hammers.
Piles, some of them underreamed, are between 406mm and 610mm diameter and are up to 30m deep, founded in the underlying hard Grade 1 Granite bedrock at about 10m depth. Pile bores take up to two days to drill, with rock sockets alone taking an average of six hours to form.
Gammon Skanska has built temporary platforms to carry vehicles over the tunnel and station excavations. To cope with overhangs from nearby shops and hotels, HD Engineering fitted some of its rigs with shorter masts. Two of the HD200 and HD205P rigs have been fitted with 5.7m masts instead of their normal 9.8m and 13m masts.
The 10,000m 2, 11m deep station excavation is well under way, as is the 520m long, up to 20m deep cut and cover excavation for the tunnel along Salisbury Road. While 1,500 piles are planned for the contracts, the final total is expected to change as work progresses.