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Eye on the main chance

Tunnelling: Trenchless technology is taking off in a big way in Hong Kong, with major projects under way. Ian Vickridge looks at the latest developments

If ever a city needed trenchless technology it is Hong Kong - high density, high tech and high traffic congestion. And the technology is about take off in a big way in this vibrant region of southern China.

Preparations are under way for extensive use of trenchless technology for installing and rehabilitating utility services under the busy streets and two major leading-edge technology directional drilling contracts have just been completed.

The first was to meet the water supply needs of a new development on Ma Wan Island and included installation of two 300mm diameter pipelines under the 1.1km wide, 45m deep Ma Wan channel.

A total 1.4km was drilled though difficult and complex ground with granite and volcanic tuffs, intersected by faults, and overlain in the shallower sections by marine deposits.

Although the internal diameter of each pipe is 315mm, the final reamed size of each bore was a massive 800mm diameter, to meet conditions laid down by Hong Kong's Water Supplies Department (WSD).

Normal requirements for horizontal directional drilling (HDD) are that the bore be 1.25 to 1.5 times the diameter of the installed product. The HDPE pipe, with an outside diameter of 457.2mm, was inserted within a 600mm epoxy coated steel pipe with an additional external coating of polymer concrete to protect from abrasion.

While the main contractor Leighton and its specialist drilling subcontractor Lucas were busy on this project, another large directional drilling contract was let - to install twin ducts for electricity supply cables across the Ma Wan channel, a few hundred metres away from the WSD project.

Lucas again undertook this difficult hard rock drilling, this time as subcontractor to Skanska. The contract was made even more complex by the fact that it is curved in plan as well in elevation.

Now it is the turn of smaller directional drilling rigs. An underground asset management study in the late 1990s showed a significant proportion of Hong Kong's water mains were approaching the end of their service life and recommended that half of the system (3,000km) should be replaced or rehabilitated over the next 20 years.

Investigation of the first 300km has already been carried out and the WSD has emphasised that trenchless methods should be used where possible.

Detailed design is now under way and contracts for the work will be let late this year.

The WSD plans a continuing cycle of investigation, design and construction contracts to complete the programme within the next 20 years. A study for the second 300km has just begun.

Although greater use of trenchless technology could undoubtedly help minimise the impact of the work, there are particular difficulties to overcome in Hong Kong.

First, the WSD has a public commitment to limit any disruption of water supply to eight hours (compared with 30 hours in the UK), making it almost impossible to carry out rehabilitation work without using temporary bypass systems, which adds to the overall cost.

As well as the large number of connections and the need to keep busy pedestrian routes open, the situation is further complicated by the close proximity of buried utilities, the large number of bends in the pipes and the concrete surround to much of the pipework.

However it is expected that well over half of the work will be done by trenchless methods.

And with the lack of experience among local contractors, this leaves plenty of scope for specialist companies in Europe, the US and elsewhere to develop working relationships with Hong Kong contractors.

The WSD is not the only government department promoting trenchless technology in Hong Kong. The Drainage Services Department (DSD) recently called for tenders for more than 4km of 1.8m diameter sewers to be installed at depths of up to 17m in the densely developed areas of Wan Chai East and North Point on Hong Kong Island.

The DSD wants most of this built using trenchless methods to minimise disruption to traffic.

The works are scheduled to begin in April and take about 43 months.

With the immense potential for growth in the use of trenchless methods, it is no surprise that a major exhibition and conference, Trenchless Asia, will be held in Hong Kong in November.

This is being organised by NoDig Conferences and Exhibitions with the support of the China Hong Kong Society for Trenchless Technology and the International Society for Trenchless Technology. It is expected to attract exhibitors from all over the world, who will have the opportunity of demonstrating their products and systems to an eager audience from Hong Kong, China and other South East Asian countries.

Ian Vickridge is the executive secretary of the UK Society for Trenchless Technology and an independent consultant specialising in trenchless technology.

INFOPLUS Further details of the Trenchless Asia exhibition and conference can be found at www. westrade. co. uk CHKSTT can be seen at www. chkstt. org. hk For ISTT visit www.ISTT. com

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