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IP3 Bridges - Replacement / Reinforcement of pillars
Bridge over the River Mondego in Cunhedo, Bridge over the Ribeira de Mortágua and Bridge over the River Dão in Santa Comba Dão at IP3.
Rehabilitation / Replacement of pillars without interruption of traffic.
The first two bridges are integrated into the reservoir of Açude da Raiva and the third into the reservoir of Barragem da Aguieira. The three works present a similar structural typology and the same type of pathologies in the pillars.
The bridges are made up of beamed decks of pre-stressed reinforced concrete, 15.2 m wide and spans of 40.0 m. The pillars are made up of cylindrical shafts with a diameter of 2.60 m, topped by prestressed laminar capitals. The foundations of the pillars are straight, with a circular or elliptical shape. The works were built between 1976 and 1979 according to projects by Prof. Edgar Cardoso.
The set of the shafts of the pillars shows anomalies resulting from the degradation caused by alkali-silica reactions that gave rise to more or less severe cracking, jeopardizing the maintenance of the works and thus making it necessary to repair or replace the pillars.
Bridge over the Mondego River in Cunhedo
Bridge over the River Dão in Santa Comba Dão
Bridge over the Ribeira de Mortágua
The solution developed consists in the execution of an annular section shaft, involving the existing one, founded on micro-piles. The new shaft will have a thickness of 0.30 m and an outer diameter of 3.40 m, guaranteeing a gap of 0.10 m around the perimeter of the existing pillars in order to allow their expansion without restrictions, due to the alkali-silica reactions that will continue to elapse.
The foundation consists of a set of micro-piles with a high load capacity, topped by a massive ring-shaped pile, executed, like the shaft, around the current pillar. The micropiles are made from the surface, intersecting the existing footings. At the top, at the capital level, the new shaft is connected to the existing one through bolts.
Three-dimensional visualization of the recommended solution
In an intervention of this type, the constructive process assumes an accentuated importance. Initially, the recommended solution consisted in the execution of cofferdams around the pillars that allowed the dry execution of the new structures, but, during the development of the project, the option for cofferdams that could reach heights of the order of 20.0 m, implanted in foundation soils constituted essentially by landfills and alluviums, led to the development of an alternative and innovative constructive solution that allows the dry execution of new structures without the use of cofferdams.
Project: 2011
Client: EP - Estradas de Portugal EPE