Lessons Learned Repairing Factory Bridges: Astiñene and Deba

Abstract

In spite of the stone-masonry bridges toughness and durability, their integrity may be compromised when built on soils with low carrying capacity for several reasons: design flaws, limitations in technology and knowledge or increase of solicitations. The displacement or rotation imposed by the collapse of the foundation of such a stiff structure causes the formation of hinges through the appearance of cracks and loss of pieces from any of their main elements (piers, arch, spandrel), as it tries to accommodate itself to a new geometry. The absence of strength against tensile forces and the conversion of the structure in a mechanism due to the excessive number of hinges can lead it to its collapse; the fall of one of the spans produces generally a chain reaction leading to the failure the rest of the structure as the piers reach a situation in which the horizontal forces are not compensated anymore.

We will present, from the specialized company point of view, two recent rehabilitation and repair experiences carried out as emergencies on stone-masonry bridges in Gipuzkoa, after a sudden settling.

On Astiñene bridge in San Sebastian, the rehabilitation works required, for the underpinning of the foundations, the use of a micropiling machine that worked from the deck with an innovative system (Sonic Drilling). The weight of this machine provoked horizontal loads in the vault that were compensated by means of pretressing bars.

On the old bridge of Deba, the works supposed a technical challenge as it was required to launch, from a very limited space, an auxiliary structure over the two spans affected by the settling of one of the piers; launched after the underpinning of the foundations, the structure allows to sustain the arches by means of support rods.