A39 CANNINGTON CULVERT BOX JACK

February – October 2016

BRIEF DESCRIPTION

A key client of MDA, Kier TVO, came to us with a difficult Flood Defence Scheme project crossing the main road A39 leading into Cannington and Hinkley Point. MDA were involved throughout the value engineering stage and suggested installing a mabey bridge solution over the existing road and then installing steel headings underneath to create the space to jack the culvert units through. This was a quadruple cell culvert that only had 1m of clearance from the soffit to the road level and was an extremely technically challenging project.

SCOPE OF WORK

MDA first had to plan and co-ordinate with Kier TVO, the Highways Agency and EDF Energy, a road closure for the A39 to enable us to install the temporary support bridge. Once the road was closed, MDA had eight hours to excavate the existing road to house the temporary bridge bearings, set up the 200t crane in the adjacent field and deliver and lift the 40t, 30m long bridge into position.

Once the bridge was lifted into position, we had to create on/off vehicle ramps from compacted material and tarmac them so that the bridge would be able to receive traffic that morning. This process was successfully completed and then repeated on the following night to install the other half of the bridge on the Southbound lane.

With the traffic on the road running smoothly, MDA could concentrate on tunnelling under the road to make space for the 48 box culverts that were needed by the flood defence scheme. With impeccable setting out and engineering we constructed two tunnels at the same time in cells 1 and 3 leaving space for cells 2 and 4 to be tunnelled after. This meant that the least amount of the road material was being disturbed.

With the four tunnels complete and the base concreted, the work begin to lift the 8.9t box culvert unit onto the concrete base slab and then jack it into position underneath the live A39 above. The works were extremely smoothly and were delivered on time and budget with a perfect safety record.

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