Trials of a chemical remediation technique new to Hong Kong are opening the way for redevelopment of the territory’s old Kai Tak Airport. Claire Symes reports.
Hong Kong’s notorious whiteknuckle approach for air passengers became a thing of the past in 1997 with the closure of Kai Tak Airport and the opening of its replacement, Chek Lap Kok. Now work is under way to develop Kai Tak as a sustainable urban district.
One of the first consultancy contracts to be let for the 460ha South East Kowloon Redevelopment (SEKR) is for land reclamation. In spring, Scott Wilson and Arup were awarded the JV contract to reclaim the Kai Tak Approach Channel east of the old runway.
Scott Wilson Hong Kong director Mike Chalmers says: ‘The Hong Kong government’s Territory Development Department intends to develop the old airport as a ‘green’ city which will be home to more than 266,000 people.
The entire development will cost about HK$36,000M [£3bn] and is expected to be finished by 2015.’ Kai Tak Airport was built in the 1950s and the land reclamation scheme for the runway was designed by Scott Wilson in its first project in the territory. The Kai Tak Approach Channel is an open body of water, fed by the Kai Tak Nullah, which runs parallel to the runway and widens out at the southern end to provide a typhoon shelter for local boats.
Under the SEKR, 30ha of the channel is to be reclaimed. Scott Wilson and Arup are responsible for the design, tendering and construction supervision. The typhoon shelter will stay for now but may be reclaimed later. Work is expected to take about six years.
Clean-up is necessary before reclamation can begin. ‘The Kai Tak Approach Channel is notorious for its unpleasant odour, caused by heavy organic pollution in sediment on the bed of the channel, ’ says Chalmers.
The channel’s catchment area is Kowloon and the surrounding hills. Before the introduction of sewerage in the area raw sewage used to be washed into the channel along with surface water.
‘Much of the Kowloon district is now connected to the main sewer network, but the pollution in the channel has remained untreated, ’ Chalmers explains.
‘We are working on laboratory testing to apply a chemical remediation technique - which was developed in America and has never before been used in Hong Kong - to carry out the clean-up insitu.’ The technique involves injecting the sediment with a mix that contains an oxidising agent. This will be done once reclamation has raised the ground above tide level. Different mixes are being tested in the laboratory before field trials to assess fully the effectiveness of the technique.
An exsitu remediation technique - again new to Hong Kong - is also being evaluated. This involves chemically treating dredged sediment which, once decontaminated, is re-used in the reclamation.
‘Use of either method will mean that the contaminated mud will not have to be excavated and deposited in landfill or to an offshore dump site, ’ says Chalmers.
‘Landfill space is at a premium in Hong Kong, so these new remediation methods have a big advantage.
‘We are hoping to be able to use the insitu method as it will avoid the odour problem which dredging the sediments would cause.’ The main reclamation work will be carried out using suitable fill material sourced from demolition and construction sites elsewhere in Hong Kong. Waste from demolition of the former airport’s taxiway bridge and seawalls will be processed and reused. Suitable rock armour from the existing seawalls will be stockpiled and re-used on slopes built to protect the newly reclaimed land.
Consolidation will be accelerated by surcharging which will be carried out by placing between 2m and 6m of additional fill on top of the final ground level.
Vertical drains installed in the fill material will be instrumented with piezometers and inclinometers to monitor settlement.
The joint venture will also design the diversion works for the Kai Tak Channel. ‘The open channel will be replaced by an enclosed culvert at its northern end which will cut across the old runway to discharge into the sea, ’ says Chalmers. ‘The culvert is likely to be built using reinforced box section culverts and may be fitted with tidal gates at its outfall to prevent inundation and flooding in upstream areas during tidal surges.’ Design work for the phased reclamation and culvert is well under way and the first contracts for construction are expected to be awarded in 2003. Work is expected take about 30 months.