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Hong Kong starts to clean up its act

A new technique to improve the quality of bored piles could help bring Hong Kong piling contractors in from the cold after recent piling scandals in the region. Keith Wallis reports.

Araft of corruption, fraud and shoddy work scandals over the past three years has made the piling sector the pariahs of Hong Kong's construction industry.

The problems have already cost the job of Rosanna Wong Yick-ming, former chair of the Housing Authority, after a probe by local legislators into shoddy piling on government housing sites.

About 20 engineers, technicians and other construction staff have been jailed for their role in either perpetrating or covering up short piling which was discovered on commercial and housing sites all over Hong Kong. Many more have been arrested as anti-graft officers and police continue to investigate several other cases.

The Housing Department has tightened its prequalification and selection criteria in an attempt to improve standard in the construction of bored piling and foundations.

It is this background that led local foundation contractor Tysan Foundation to develop a new, patented bored piling construction technique that it claims guarantees the integrity of bored piling works.The firm says the method is suitable for all types of bored piles, regardless of depth or diameter.

Tysan Foundation executive director David Chiu says there have always been quality issues of trying to construct bored piles in Hong Kong.These include ensuring the piles are properly founded into bedrock, rather than on massive underground boulders, and that the base of the pile is clean and free of water.

This last problem poses particular difficulties, especially as piles are often bored 30m-60m into the underlying rock, well below groundwater level. As a result, it is almost impossible to ensure that the base of the pile is dry and free of debris, or that groundwater does not wash out the concrete, he says.

In an effort to overcome these challenges, Hong Kong piling contractors have traditionally used a combination of polystyrene chips, a steel tremie pipe and a placement hopper.

The chips, inserted into the tremie pipe, are intended to create a protective barrier between any water in the typically 200mm-300mm diameter pipe and the concrete.

The hopper controls the flow of concrete into the tremie pipe.

But the system is not foolproof and as Tysan's patent document makes clear, water does come into contact with the concrete.

'There is still a certain degree of contact between the concrete and the water inside the tremie pipe during the initial down flow of the concrete towards the bottom of the tremie pipe.Once the concrete emits from the bottom of the tremie, the stoppers of polystyrene surface and serve no further use of insulating the concrete from the water, washing out the cement or causing honeycombing, ' it states.

Also, skips are manually operated and have limited capacity of between 6m 3and 9m 3, so the downward surge force is slow, especially on long pile depths, and may not dislodge sediments at the base of the pile, Chiu says.

To overcome these irregularities, Tysan Foundation spent about a year developing alternative methods, largely by trial and error, until finalising its system which was patented at the end of last year.

Tysan has replaced the polystyrene chips with a cementitious grout which is lighter than the concrete, but heavier than water, consequently providing an insulating barrier in the tremie pipe between both. And as the grout and concrete are both cementitious materials concrete imperfections are eliminated, the firm says.

A hydraulically-controlled discharger and sliding door together with a concrete skip has replaced the manuallyoperated hopper. This gives a much larger gravitational weight to the concrete, with a faster downward surge force.

This means it can displace spoil at the base of the pile.

'We tried various permutations involving the discharge skip, polystyrene chips, tremie pipe and concrete mix, ' explains Tysan Foundation director Lai Kok-Wai. Seven trial piles were then constructed using the hydraulic hopper, tremie pipe and grout.

'The results from the cores were very good.There was no washing away of the cement and no honeycombing, ' says Chiu.

As a result Tysan introduced the method on various sites including phases one and two of the Cyberport project at Pokfulam, the Mass Transit Railway Corporation's Tseung Kwan O extension and several government building and housing projects.

'We cored the first 300 piles and they were all perfect.

This has proved our system so now we only core one or two, 'Chiu says.

The firm has built 'several hundred piles using the patented system' says Tysan Holdings vice chairman and managing director Victor Fung.'The success rate has been 100%.'

Fung confirms that the method is more expensive than traditional techniques, costing an extra HK$10,000HK$20,000 (some £890 to £1800) per pile depending on the length and diameter of the installation.

But this is 'negligible'Fung says, given that installing a 60m deep, 3m diameter pile can cost £180,000.'Especially when weighed against the far greater damages that can be imposed for late completion, 'he adds.'In terms of the repair and delays the costs are minimal. If one pile goes wrong then it holds up the entire job, leaving the piling contractor liable for liquidated damages.'' The patent is effective for eight years and Tysan is already in talks with other contractors to allow them to use the system under a licensing agreement. Fung says that, while he would be pleased if Tysan could make some money out of its invention, he is also conscious of the need to lift the integrity of the industry.'We're hoping to share with the industry and help it, ''he says.

Although the firm is aware that several piling contractors are developing their own systems that may be similar to Tysan's technique, Chiu says the development cost is expensive. If contractors want to develop alternatives, he warns, they will 'still have to go through the same painful step we went through, spending time and money developing a practical solution' Fung adds that government officials, including the Buildings Department, have been very responsive to Tysan's invention.'It is one less problem they have to deal with, 'he says.

'Hopefully, what we have developed will restore some public confidence in the piling sector and construction industry generally, 'he says.

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