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Partnership pays off

A LONG-TERM partnership of London Underground (LUL), consultant Mott MacDonald and contractor Skanska Cementation Foundations has played a vital role in the success of a five-year programme to manage 100km of embankments on LUL's surface network.

'By working in an integrated design and construct team sharing staff as well as ideas, we were free to brainstorm new concepts and devise innovative approaches that immediately saved time and money, ' says Bill Rankin, director of Mott MacDonald's foundations and geotechnics division and director of the project.

'Through an active feedback loop involving the same people over several years, we were able to go on refining and improving the efficiency, cost-effectiveness and sustainability of those solutions, ' he says.

One result has been a reduction in the cost of emergency repairs from £5000 per metre in 1995, when the programme began, to £1700 by the end of last year a 20% fall year on year.

LUL's earth structures programme was prompted by increasing stability problems in the early 1990s, which were seriously disrupting train services. The plan involved more than 40 projects and aimed to manage stability and reduce track deformation while radically cutting costs. It also aimed to improve the appearance and promote sustainability of 100km of embankments, most over 75 years old and some dating back to the 1870s.

Rankin says research into the mechanisms driving embankment movement formed a central part of the programme, which the team then applied to design and construction.

'Spinning small embankment models in Cambridge University's centrifuge was an important part of our research, 'he says.'Exerting forces of 60 times gravity during a 24-hour test had the effect of scaling the models up to life size and simulating a 30-year period.'

Skanska Cementation's CemRailBeam is one of the innovations to come out of the programme.The rapid precast capping beam system has been used with bored pile walls and slope vegetation to stabilise embankments on this and other rail projects (Ground Engineering June 2000), dramatically speeding up construction time.

Project specific key performance indicators (KPIs) have proved to be another vital tool, says Rankin. One KPI was the volume of concrete used in stabilisation as a percentage of the overall earth structure volume. This has been consistently lowered throughout the project.

'Concrete consumption was reduced by over 50% in piles and 30% in capping beams contributing to sustainability as well as value for money, ' Rankin says.

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