Marine mud no longer a nuisance for developers

A government engineer has found an innovative way to fortify soft seabed mud to provide a solid building foundation.

Traditionally, the mud has been regarded as a nuisance for construction, being treated as waste and dumped in landfills or out at sea because it is too soft and will not harden when compressed.

But now a solution developed by Housing Authority engineer Patrick Leung Pak-wai - the first of its kind in the world - could help reduce construction costs as well as damage to the environment.

He found that a mix of 80 per cent marine mud, 15 per cent sand and 5 per cent cement can be compressed and hardened to make it strong enough to support a building's foundations.

'It's a real headache dealing with marine mud,' said Leung, who is working on one of the construction sites at the former Kai Tai airport where the authority is developing public rental housing.

Leung's approach overcomes the root of the problem, which is that marine mud on its own is too fine and soft and retains too much water, making it slippery and sticky.

The innovation could save the government more than HK$8 million on waste disposal alone - HK$3.54 million for landfill disposal and HK$4.62 million to dump the unwanted mud into the sea.

The authority said that the construction site for site 1A of the Kai Tak Public Rental Housing Development would require 12,000 cubic metres of marine mud to be excavated - an amount equivalent to five standard Olympic-sized swimming pools.

It would have to be dumped either into a landfill or at sea. It costs HK$250 to dump one cubic metre of waste at a landfill.

Hong Kong faces an acute shortage of landfill space. Three landfills handle 9,000 tonnes of solid waste a day - the marine mud from the Kai Tai site would take up three days' capacity of the landfills.

'If we were to transport all the mud to the landfills, it would have taken 3,000 round trips,' Leung said. 'Now we can save on fuel too.'

Leung's solution is cost-efficient. Sand and cement are freely available at the construction site and fortifying the marine mud to make it usable in building foundations saves on construction time.

And that's not to mention the benefits to the environment it brings. 'You can imagine dumping all that mud into the sea won't do much good for marine life,' Leung said.

The cement also serves to hold contaminants in place - further reducing the risk of damage to the ecosystem - though Hong Kong was not as industrially developed in the 1920s when the land was reclaimed at the Kai Tak site as it is now, so the marine mud contains few heavy metals and hazardous contaminants.

Leung said his innovation may or may not affect housing prices, as there were other factors to consider.

This environment-friendly treatment of marine mud will now be used at other authority construction sites where there is marine mud, such as another at Kai Tak and an area in Tseung Kwan O.

30%

The percentage of Hong Kong people living in public rental flats. The Housing Authority caters for people on low incomes