Best solution for new Hong Kong island residents

The pressure for new building land in Hong Kong remains intense and a new

road bridge has recently allowed the small island of Ma Wan to become available

for residential development.

The risk analysis identified that a sub-sea pipeline, whether on the sea bed

or in a shallow trench, was extremely vulnerable to the shipping activities

in the area and that twin pipelines laid someway apart did not appreciably mitigate

this risk. The tunnelled solution did not have the same in-service risks but

was very costly, and the costs were not determinate due to geological conditions,

as already established on comparable projects.

Horizontal directional drilling (HDD) was attractive because the installation

cost and subsequent operational risks were both lower than other alternatives,

however the risk analysis recognised that the method would be outside the current

application envelope because it involved drilling through very hard granite

over a large distance.

WRc was aware of the advances that were taking place in HDD technology and

determined that a wellengineered solution was both feasible and economic, offering

considerable cost advantages over other options and a low level of risk. A twin

HDD installation was recommended and the project was completed in two years.

Construction commenced with the drilling of a 100mm pilot hole for each pipeline.

These holes were then reamed out to the final diameter of one metre in a three-pass

operation. The bore was lined with a continuously welded steel sleeve within

which a thick walled welded polyethylene pipe provides the highpressure conduit

that delivers water to the new developments on the island.

As John Cant of WRc said, ‘WRc monitor global advances in water technology

and make these available to individual water utility companies. The involvement

of WRc at every stage of the Ma Wan project, from theoretical analysis to on-site

supervision of highquality welding operations, has ensured that the residents

of this new community are now able to benefit from a unique highquality solution.’

A subsea pipeline was rejected in favour of a twin HDD installation.