Best solution for new Hong Kong island residents
The identification of the most economic solution for a pipeline is a specialist task when water utilities are faced with a combination of difficult ground conditions, an unusual location and an awareness that savings may result from an innovative approach. WRc, the UK-based international water and environment consultancy has recently contributed to a unique solution in Hong Kong.
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.