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Underpinning a good reputation In this spotlight, Ground Engineering looks at how the Association of Underpinning Contractors is improving the industry's image, plus some innovative stabilising soluti

Efforts spearheaded by the Association of Underpinning Contractors to improve the underpinning's cowboy image are beginning to pay dividends.

ASUC now has 14 members and reckons to represent about half of the UK industry.

Its growth has been particularly strong over the last few years, and for the immediate future ASUC is targeting smaller companies, with an aim of increasing its representation to about two thirds.

Many believe there is now real momentum within the organisation, and that initiatives such as its insurance-backed guarantee scheme have helped the standing of both the industry and ASUC's members.

The launch last year of the insurance-backed guarantee scheme, after three years of negotiation, could not have been more timely - it has helped ASUC to shake off the bad press generated by the poor practices and ultimate expulsion of one of its founder members.

Members range in size from multimillion pound turnover piling contractors which offer minipiling, to traditional pier and beam underpinners with less than pounds1M turnover.

Demand for underpinning mainly depends upon geology. High plasticity shrinkable clays, such as London Clay, Gault or Weald Clay, present the greatest risk. Other causes are moisture susceptible fine sands and silts which can become a problem if a property has leaking drains.

Because these ground conditions occur predominantly in south east England, more than a third of the UK's underpinning takes place in this region, and the majority of underpinning contractors are based there.

Their common factor, says ASUC immediate past chairman John Patch of Roger Bullivant, is the ability to deliver specialist underpinning work, with 'that extra bit of service and expertise. Our members are not local builders who happen to do a bit of traditional dig-out work'.

According to Patch, ASUC's insurance backed guarantee, which kicks in if problems occur on work carried out by a member company that has since become insolvent, is really a second level of protection for the client. Of more immediate benefit is that under the rules of membership, companies are obliged to put work right if defects are found.

Patch says ASUC takes the policing of its membership rules very seriously and has acted against non-compliant members in the past. 'We must abide by the rules,' he says. 'There is still an image problem with underpinning in some quarters, and we want to be disassociated from the cowboy image.'

ASUC has certainly managed to pull in impressive allies, giving credibility to its claims and aspirations. Both the National House Building Council and Building Research Establishment are honorary members, and it is a sign of ASUC's intentions that both these august organisations take an active role. For example, BRE provided the venue for a one day conference on behalf of ASUC last month, which included a presentation of BRE's research into high plasticity clays at Chattenden in Kent.

This long term monitoring project is helping to provide scientific data needed to support design of underpinning schemes, particularly where the problem is heave resulting from the removal of trees, which is less well understood than settlement induced by trees taking moisture from the ground.

BRE's Mike Crilly reported that eight years after the removal of trees at Chattenden, heave is still taking place. To date there has been around 140mm upward movement, and significantly there is no sign of rehydration below 2.5m depth - the clay is still desiccated and presumably the potential for further heave is considerable. Crilly says the ground has probably only recovered about half the likely total.

Other issues on the ASUC agenda include technical standards and health and safety: it is preparing documents on both areas. It is soon to launch the first of its technical standards. These should evolve into a textbook of good practice for the full range of techniques from traditional pad, to micropiling, grouting and other innovative solutions.

Meanwhile its health and safety committee is drawing up guidelines which spell out safety requirements for deep underpinning work which have become much stricter since the introduction of CDM regulations.

In recent years ASUC has forged a close relationship with the Federation of Piling Specialists. There is some overlap in membership, and the fact that Patch is a key player in both organisations is undoubtedly an important factor in their coming together on issues such as retention and quality of site investigation.

Astonishingly, around 30% of underpinning schemes go ahead without any site investigation information whatsoever, reports Patch, so this is clearly a major issue. Two months ago ASUC published guidance setting out the minimum level and standard of site investigation required for the different types of underpinning work, and long term is lobbying to make site investigation a requirement of building regulations.

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