Exceeding customer expectations

When disaster struck the newly-constructed Boadilla Tunnel outside Madrid, Spain, the contractor, a joint venture of the four biggest Spanish construction companies, needed a fast, high-quality and cost-effective way of rebuilding it. Interserve's Equipment Services division provided the solution.

The M50 motorway will, when complete, circle Madrid in much the same way as the M25 circles London. A section of this outer ring road passes through the residential community of Boadilla, some 9 miles to the west of Madrid. In order to maintain the community's integrity an artificial tunnel, 225 metres long and designed to carry three lanes of traffic, was constructed by excavating the ground, creating a tunnel shell and finally covering the shell with soil. It was during this last stage that things went wrong: part of the tunnel collapsed under the weight of the earth on top of it.

The contractor called in specialist engineers from Interserve Equipment Services to devise a method of rebuilding the damaged section. Although Interserve had not been involved in the original project, its design offered significant savings in construction time compared to the alternatives considered. The design began with building a falsework frame outside the tunnel then placing curved formwork panels on top on lengthways steel beams. The whole structure was towed into the tunnel in modules and the new section of tunnel shell was then created by pouring concrete around the form in three carefully-controlled operations, the equipment being moved along the freshly-created tunnel between each pour.

This approach, using largely standard materials and avoiding the need for a rail-mounted system, reduced the amount of equipment needed and saved the team valuable time on site – with the result that this section of the M50, carrying approximately 80,000 cars a day, will be open some two-to-three months earlier than would otherwise have been possible.

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