CONCRETE | TECHNICAL
Above: Mammoet’s transport solution negotiated the tight headroom and clearances in the tunnel
As ever, the clock would be ticking too, while other
construction activities had to keep going on the busy project programme. Options? Feeding the 70 tonnes precast trusses into the tight
site underground space ruled out using tower cranes as the main option. But they would play a role. The main transport solution was, instead, to employ
multi-wheeled, highly manoeuvrable transport trailers – carrying packing structures. A few trusses could then be carried at once, slowly, carefully, down into the tunnel. Mammoet proposed the solution as a custom packing
structure positioned on self-propelled modular trailers (SPMTs). Its solution would be able move up to four of the heavy concrete trusses at once and transport them to the installation points. That would be important to the success of the construction programme. First, though, the equipment configuration was put
through its paces, off site. Mammoet says “a series of dry runs” of the packing structure on the SPMTs were performed. Part of the testing was to ensure the same configuration would serve both sizes of truss.
Then the machines got to work moving the trusses. And, that is where the conventional site cranes come
in: a tower crane had the job of lowering the concrete trusses onto the packing structures, that sat on the SPMTs. Then the self-propelled machine moved into the tunnel. The first set of trusses to be transported had a
combined mass of 193 tonnes. They went the farthest distance underground, to the far end of the station, slowly travelling a distance of 150m. The hydraulic suspension and electrical multi-steering
system of the SPMTs enabled them to carefully position the trusses in their designated positions. Altogether, in the first phase of work, a total of 55
trusses were placed, each with a mass of 48.3 tonnes. The remaining four trusses were extra-large, at 70 tonnes each, and installed in the second phase of the operation. By taking multiple trusses at a time, each transport journey installed up to four trusses, totalling approximately 15 iterations, says Mammoet. Fergus McHugh, Project Manager at Kenny
Constructions, says, “This was a challenging scope of works, yet everything went according to plan.”
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