With an lengtht 508m and intersected by a multitude of underground infrastructure, notably four railway tunnels built between 1940 and 1990, the road tunnel under the Plaça de Les Glòries in Barcelona is configured with four main areas, access ramps at both ends and two central shafts between tunnels. Built between diaphragm walls, the four spaces are connected by three horizontal passes under the existing tunnels. The central shafts reach excavation depths of up to 26m, 13 of them below the water table level and with bracing on the roof. Two levels of intermediate supports are necessary and a double invert at the bottom that is supported on the side walls of the shafts and under a central alignment of low walls.
The three passes under the railway tunnels have a twin cell box geometry and were built by successive advances under a bank of steel and concrete rings 1,100 mm in diameter, sunk beforehand. The bank of rings formed protection during the phase of excavation in steps while providing solidity and stiffness to the infrastructures above, which remained in service during their construction.