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Race to prevent London mains burst

COMMUTERS AND residents in North London face a summer of disruption after Thames Water revealed it may have to excavate up to 77 buried access hatches on a key water main.

The company admitted this week that a spectacular burst in March which flooded Hanger Lane and caused traffic chaos (NCE 11 March) could be repeated along other parts of the 1.5m diameter main, which runs for 21km under built-up areas from Kempton Park in the west to Cricklewood.

It had claimed that a programme of checks carried out 18 months ago showed the steel pipe to be in good order. But an urgent new series of investigations is now being carried out into the condition of bolts on access hatches which are thought to be at risk of failing.

A Thames spokesman said the company would start by excavating and replacing bolts on 22 access hatches located on a 5km section of the main from Hanger Lane to Cricklewood. It will further uncover and examine two hatches in each of the three other sections of the main to assess the scale of the problem.

As many as 77 of the 0.6m diameter hatches may eventually have to be excavated.

An independent investigation by research establishment DERA blamed the Hanger Lane burst on an access hatch failing due to corrosion of the bolts holding it down. The report claims the bolts were too short and had no protective bitumen coating on their threads.

A Thames spokeswoman claimed aggressive ground conditions and massive surge forces may also have contributed to the accelerated corrosion of the bolts. She admitted the company is now investigating how much of its 1,000km of steel water mains are of similar age, construction and in similar ground conditions.

'Part of what we are doing is carrying out a risk assessment for the future,' she said.

The first half of the Hanger Lane to Cricklewood stretch will be closed off next month when work to replace bolts begins. Work on the second half of the section is due to start in July.

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