Cut-and-cover Tunnels. Txorierri, Vizcaya, Spain

Txorierri Cut & Cover Tunnels are located on the north of Bilbao. The structures are designed as precast modules covering both 3-lane carriageways of the motorway. The Owner called for an urgent assessment of the pathology, consisting of very extensive cracking.

Cut-and-cover tunnels designed with precast modules are an excellent solution There is a need to make them as slender as possible, for transportation reasons, which makes them very sensitive to the conditions of the ground an the fill. Inadequate choice of fill material and compaction seems to have been the problem in this case, as it was later found by records of the execution and by a soil investigation. This was confirmed by analyses, done in this case with a general-purpose Finite Elements model, taking into account material non-linearity through Mohr-Coulomb plastification model

The remedial measures started by reducing the soil cover to levels which would guarantee absence of excessive cracking, followed by sealing all the existing cracks.

SILGA did visual inspection, structural analysis and design of remedial measures.