Depth equivalent to 50-storey office building
A significant step has been made in the construction of the Harbour Area Treatment Scheme (HATS) when Drainage Services Department last month achieved breakthrough for the scheme’s deepest section, which also happens to be Hong Kong’s deepest tunnel.
The section concerned, the 3.2 kilometre section from North Point to Wan Chai of the HATS Stage 2A sewage scheme, is more than 160 metres below sea level.
“The 160 metre vertical distance is equivalent to the height of a 50-odd storey commercial building,” the department said in a press release last Friday.
Work started on Stage 2A, which is 21 kilometres in total length, in July 2009.
The depths of the sections vary from 70 metres to 160 metres below sea level.
The construction method used was drill-and-blast for the dropshaft excavation works and deep tunnels.
The first blast for the North Point to Wan Chai section, which Gammon Construction is responsible for, was conducted in July 2011 and breakthrough was achieved on 26 October.
Worth noting is the number of blasts that were required to get this far in the project.
At the officiating ceremony Director of Drainage Services Chan Chi-chiu said over 5,600 blasts were conducted for Stage 2A, probably the highest number of blasts for one single project in Hong Kong ever.
More importantly, with the severe shortage of some specialist trades in the construction industry, under the project the department trained up 13 blasting supervisors and 87 competent persons for supervising delivery of explosives.
Stage 2A, with an approved project estimate of HK$9.2 billion, will collect sewage from the northern and southwestern parts of Hong Kong Island and convey it to the Stonecutters Island Sewage Treatment Works on completion in late 2014.
Stage 1 of HATS, which was previously known as the Strategic Sewage Disposal Scheme, came into operation in late 2001 and treats about 75 percent of sewage generated from both sides of Victoria Harbour, significantly improving water quality in the eastern and central parts of the harbour.
So much so that the Hong Kong Amateur Swimming Association decided to revive the gruelling Cross Harbour Race in 2011, the first time it has been held since 1978.