After several flooding occurrences over the past few years, the most recent being December 2004, the Environmental Agency entered into a framework agreement with Volker Stevin for a £6M flood alleviation scheme.
During the initial planning stage, Genseed Underground Services, which has carried out numerous railway crossings using Trenchless Technology, was invited to put forward suggestions to achieve the under-track crossing.
The requirement was for a series of four pipes, each of 914mm outside diameter with a 14.3mm wall placed parallel to each other with 200mm spacing between each pipe. The drive length of each pipe was 18m. The reason for a four-pipe configuration rather than one large pipe was dictated by the constraints of depth and cover. The 914mm pipes gave a depth of 2.5m below the railway track, achieving the desired invert.
Network Rail's engineers, Corus, were concerned with any heave or settlement that might occur using any method of trenchless installation. After lengthy discussions, the engineering solution that Genseed proposed was insertion by pipe ramming.
With a 36-week lead-in time for a possession and only four possessions booked, it was critical that no unforeseen circumstances arose. Volker Stevin was able to excavate an open span close sheeted launch pit 23m long by 8m wide with a concrete base reflecting the gradient of the finished pipe.
The reception pit was 8m by 8m. Les Peck of Genseed said that, while the launch pit was very long, it did enable an 18m length of pipe to be rammed continuously without the need to stop for any circular welds on site, which would have taken a full shift.
Genseed, which owns their own Grundoram Koloss hammer, was confident that it was capable of an 18m push of 914mm pipe in the expected sandy ground conditions but could not take any chances of failure. So it contacted TT UK to obtain a Grundoram Goliath as a back-up.
The first tube was installed in around two hours using the Grundoram Koloss on the night of Saturday 1 October. The remainder of the tubes were pushed in using the larger Goliath hammer in 45-60 minutes each thus reducing the noise exposure to local residents.
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