The A-4 Motorway expansion project includes building a new tube 1,204 feet long and the renovation of extant tubes. The new tube just north of the original tunnel will have four separate lanes for traffic traveling from Amarante to Porto; the original tubes will provide passage for traffic in the opposite direction. The project will improve travel for traffic going in and out of the city of Porto.
ULMA provided a scaffolding carriage to waterproof the tunnel, a carriage to install the rebar, and one to pour concrete into the tunnel. On average, 464 cubic yards of concrete went into each cast section, with a maximum of 544 cubic yards. Ready-mix trucks were easily able to pull up to the formwork carriage and pump the concrete.
Work cycles lasted about a day and a half, with 10 to 11 hours of pouring and three hours for adjustments. The adjustments included releasing the anchoring systems, and operating the hydraulic cylinder to open the side walls and then descend the carriage. Four cycles were completed weekly.
With a single carriage, it’s possible to create all of the dimensional variety needed for a tunnel, a facet that proved ideal for this tube design with four distinct sections. The carriage also allowed for vehicles to pass during construction, which is a necessity in such projects because of all the auxiliary construction work being done.
One of the complexities posed by the project was its location in an urban center with significant geotechnical risk, characterized by thin soil cover and areas of extremely weathered granite.