Viaduct’s supporting arches demolished near twin structure

A total of 400kg of C4 was detonated to demolish the steel arches supporting a viaduct's northbound carriageway over the night of 19-20 June. Dating back to the 1970s, the bridge carries the A15 highway between the cities of Parma and La Spezia near Genoa in northern Italy. 

The 1,067m-long Gravagna Viaduct features twin structures, each with five spans: three central spans of 140m and two 65m approach spans. Each carriageway is supported by three arches, each weighing 400t and measuring 45m to 62m, that were added to reinforce the structure in 1993.

The viaduct is being demolished and rebuilt as part of a broader highway modernisation project managed by Salt, a concessionaire of the ASTM infrastructure company.

The work began in 2023 and is being executed by engineering and construction firm Itinera, a subsidiary of ASTM.

The June operation, carried out by a 60-strong team, targeted specific areas to ensure the arches fell safely without affecting the opposite carriageway or causing undue stress on the structure. Additionally, the arches’ sections in direct contact with the deck were weakened beforehand, and protective measures, such as sandbags and water, were used outside the cutting area to minimise damage.

Due to the heavy weight of the demolished arch segments (around 160t each), 3,000m³ of inert material was used to create protective dunes to absorb the vibrations from the falling pieces, reducing the impact and safeguarding the pier foundations and other structural elements.

“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 ways 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,” said ASTM in a press release. After the demolition was completed, load tests were carried out to verify the integrity of the remaining structure.

After the northbound carriageway is demolished and rebuilt, traffic will switch to it, and the same process will be repeated for the southbound structure. The entire reconstruction is expected to be completed by Easter 2027.