Itinera blasts Italian viaduct

Specialist engineering and construction company Itinera, a subsidiary of infrastructure company ASTM, has completed the explosive demolition of three metal arches supporting the decks of the northbound carriageway of the Gravagna Viaduct near Genoa in the north of Italy.

The structure, which had already been partially demolished as part of a major renovation of the Gravagna viaduct to dismantle and rebuild the 1,067-metre viaduct on the A15 Cisa highway, was built in the early 1970s and is an important main road connecting the cities of Parma and La Spezia.

The three supporting arches on the northbound carriageway were installed - along with three others on the southbound carriageway, in 1993 as part of restoration works.

A team of 60 Itinera operatives took down the northbound viaduct’s three steel supporting arches or “crutches” via an explosive event that carried out over the night of the 19 to 20 June.

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Weighing around 400 tonnes each and ranging in length from 45 to 62 metres, the arches were supported by large steel portals whose piers, as they spread apart, came to rest on the pier bases.

Itinera utilised 400 kg of explosives and gelatine for blasting the hinges, with roughly 3,000 cu m of inert material for the creation of the dunes to dampen the effects of the fall of the arches to the ground. 

While the charges were placed at five locations inside the metal boxes, the cuts were made in the centreline of the portal’s rampant arches in the horizontal and vertical directions to allow them to fall to the ground by gravity.

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Parent company ASTM said: “The part of the arch most in direct contact with the roadway deck was weakened to prevent the involvement of the homologous portal on the opposite carriageway, as well as minimising the stresses transmitted to the portal hinges and, consequently, to the piers. Outside the cutting area, protection was provided by alternating sandbags and water.

“A monitoring system consisting of about 90 inclinometers and about 90 accelerometers positioned on the piers and decks of both the northbound and the southbound carriageways was installed to monitor the effects of the demolition on both the piers and the southbound way decks, to verify that the shock wave did not create excessive stresses towards the structural parts still to be demolished.”

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