Urban tunnels under “les Glòries” square are part of the general refurbishment of this area of Barcelona. They will channel the traffic of Gran Via, one of the main accesses to the city, giving the chance of building an impressive park above them.

The initial phase of the project comprises a length of about 700 m. The tunnel is approximately straight in plan view, but its elevation consists of two ramps with no slope in the middle of the length. At both ends of the tunnel, the cars travel on ground surface, while at the deepest point of the tunnel, the alignment is about 27 m depth. Such a great depth is necessary to cross under three transverse tunnels: one for underground, and two for railways.

In transverse cross-section, the tunnel has two roads at the same level, each one suitable for three lanes. The roads are typically separated at the center by a row of concrete piles. Lateral concrete walls, 1.00 m thick at the deepest zone, are braced by three levels of concrete struts (including the roof) and the contrabóveda. Furthermore, two levels of temporary anchors are needed to reach excavation bottom.

The maximum depth of the excavation from ground level is about 30.5 m, taking into account that under the alignment there is a 1.00 m thick backfill (to pass the drainage and installations) and a 1.80 m thick contrabóveda (whose rise is 0.70 m).

Groundwater level has played a central role in the design. Its elevation is +2.00 m, considerably higher than the deepest level of the excavation, which is -15.00 m. The depth and reinforcement of walls and bottom slabs are strongly determined by groundwater. Additionally, safety against buoyancy has been carefully analyzed, obtaining vertical loads on central piles and assuring that they are not pulled up by vertical ascending pressure.

A specific construction procedure has been defined for front walls placed transversely next to the tunnels that must be crossed, in which both temporary anchors and ground treatment are used. The main objective of this procedure is to reduce horizontal movements of the front walls and, in consequence, of the existing tunnels.

Tunnel roof consists of reinforced concrete struts separated about 6.00 m between their axes. Precast hollow cores with a depth of 40 cm are placed onto them, and a topping of 10 cm thickness of in-situ concrete makes the structure monolithic. This configuration makes it possible to dig the upper part of the tunnel from ground level by means of conventional excavators. It must be remarked that due to tunnel dimensions and the wide amount of urban public utilities (culverts, installation galleries, tunnels) the use of temporary ramps is not possible.