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Aguas Santas Tunnel, Porto, Portugal

The Widest Tunnel on the Iberian Peninsula
Measuring 19.2 m in width, this mine tunnel is to become the widest on the entire Iberian Peninsula.


As part of the first phase in the expansion of the A-4 Motorway, this project includes both the construction of a new tube 367 m in length and the renovation of extant tubes. The new tube, located just north of the original tunnel, will have four separate lanes for traffic travelling from Amarante to Oporto; the original tubes will provide passage for traffic in the opposite direction. The project is designed to drastically improve travel conditions for traffic going in and out of the city of Porto.

One of the complexities posed by the project was its location in an urban centre with significant geotechnical risk, characterised by thin soil cover and areas of extremely weathered granite.

ULMA solution

ULMA’s technical team developed three separate structures in partnership with the client, in order to make work as efficient as possible.  First, a BRIO-MK scaffolding carriage was used to waterproof the entire tunnelA similar carriage was then used to install the rebar. In both cases, ULMA’s most versatile systems were combined to create carriages adjusted and optimised to meet the demands of the project without any need for oversizing. Afterward, the MK formwork carriage was used to pour the tunnel structure itself. With a single carriage it is 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, each varied at the bottom. As an additional benefit, the carriage allowed for the passage of vehicles during construction, which is a necessity in such projects. 

The MK Carriage is a high-performance, flexible solution. It offers high load-bearing capacity without compromising the ability to adapt to different sections.

The carriage features hydraulic equipment to facilitate formwork installation and stripping, as well as lowering, levelling, and advancing the entire assembly.

Using a single MK formwork carriage 12.1 m long, 10 m tall, and 19.2 m wide, the tunnel was entirely completed in three months, including assembly and disassembly.

The pace of work exceeded client expectations. Work cycles were approximately a day and a half, with 10 to 11 hours of pouring and 3 hours for advance and adjustments. Thus four cycles were completed on a weekly basis

Project data
Tunnel length 366.9 m
Longitudinal slope 0.9876%
Floor plan radius 1078.67 m


Formwork data
Formwork length 12.125 m
Thickness 500-1150 mm
Width 19.2 m
Height 10 m
m² of formwork 388 m²
Section/pour volume 230-250 m³