How was the Morandi Bridge demolished? The technical-engineering explanation

The trait of the Morandi Bridge collapsed on August 14, 2018 and was demolished on June 28, 2019 at 9:37 am before reconstruction completed in 2020. new road connection via the new Genoa San Giorgio Bridge. From 2018 to 2020, there were also various design and implementation activities of the demolition phases of the remaining part of the viaduct still standing. The demolition project, carried out in part with traditional techniques and partly through explosivesrequired the intervention of various teams of experts to follow all the phases of the work aimed at minimizing the risks associated with an uncontrolled collapse and the propagation of dust. Below we explain the main phases and the technologies implemented.

The structure of the Morandi Bridge to be demolished

It may seem strange that a collapsed bridge then needs to be demolished, with a complex and lengthy project! However, in the case of the Morandi Bridge, the demolition intervention remains necessary given the partial collapse that affected only a part of the entire viaduct. In fact, it is worth remembering that it was supported, for part of its length, by simple V-shaped piers. The remaining, although reduced, part was made up of the now well-known balanced scheme, in which the stays played a crucial structural role in ensuring the balance of the entire system.

Of this entire structure quickly described here, only a part – namely pier 9 and the decks connected to it – was actually affected by the collapse of 2018. The remainder, consistently with the static functioning of the entire structure, remained standing without difficulty and was almost unaffected by the damage caused by the crisis of the stay. For this, to make room for the new connection structure promptly designed, it was therefore necessary to create an ad hoc demolition project that minimized damage to the surrounding buildings and allowed the safe disposal of the remaining part of the existing structure.

Pre-demolition checks

The remaining part of the structure to be demolished was subjected to appropriate safety checks preliminari And load tests, necessary to test the static conditions of the system in the post-collapse condition. Two particular operations were carried out:

• The first one concerned the end of Stack 8which has undergone the insertion of a 800 ton counterweight to balance the imbalance caused by the collapse of the span resting on the pier itself.
• After having ascertained the health conditions of the actual state, the scaffolding structure was lightened of the layer of road pavingthrough scarification (i.e. removal) of the bituminous conglomerate, and the presence of new jersey lane separation.

The demolition phases

The demolition project involved several companies specialized in the sector, engaged in a 7 months of work with more than 120 workers working 24 hours a day. The group of companies involved included companies specialized in the sector of lifting and moving of large structurescompany of structural engineering and companies specialized in the sector of environmental remediation. Last but not least, the project needed a team with strong experience in the topic of demolitions with explosivesnecessary in particular processing phases.

Chronologically, the work as a whole can be divided into a series of phases:

• First of all, it was necessary to demolition of all industrial settlements below the western area. These processes, carried out with the help of mechanical organs equipped with hydraulic hammers and plierswere necessary to create suitable spaces on the ground for subsequent work.
• Subsequently, the following were carried out: removal of the so-called buffer scaffoldsthat is 5 scaffolds weighing 960 tons one simply resting on the piles. These scaffoldings they were therefore not demolished at altitudebut in fact “dismantled” And lean on on the ground. The time required to carry out this operation, for each deck, was approximately 6 hours. Consider also that for each descent of a buffer deck, an ad-hoc structural check was necessary to understand how and what the removal of a specific piece would entail: the remaining structure was therefore checked through structural calculations step by step!

• After the removal of the buffer scaffolding, all Piers 3 to 8 were gradually demolished using cranes and mechanical meanswithout using explosives. Only at the end of these demolitions were the first two piles removed, which were also treacherous because they were positioned on a slope that was difficult to reach.
• The final part of the demolition process took place through explosives and concerned pile 10 and 11: the latter, both made using the aforementioned balanced system with pre-stressed stays. This is perhaps the most delicate phase of the entire process, although the shortest from the point of view of the actual demolition (about 6 seconds!).

The study of the explosives system

The study of design and implementation of the demolition using explosives deserves a separate description. This phase also made it necessary to partial demolition of buildings around the remaining piles, as well as the connection of the viaduct decks with the neighboring highway, in order to avoid possible damage caused by the explosion. However, the additional complication that occurred at this stage was that of having found traces of asbestos in the concrete making up the bridge. Therefore, the spread of dust due to the explosion could have caused permanent damage to the health of the inhabitants. To avoid this problem, the spread of dust was countered by a concomitant water explosion. To this end, 2500 m have been built² Of artificial pools and a synchronous explosion system of the structure contemporary with the pools themselves: the controlled explosion of the water pools ensured the formation of a protective wall against the propagation of asbestos dust. The estimate of the volume of water mobilized during the explosion is 2.5 million liters!!

They have been used 550 charges for a total of approximately 500 kg of dynamite. Added to these are another 30 kg of explosives for the demolition of the stays of pile 11 which, according to the project, required a break a few fractions of a second before the piles remaining, to avoid damaging the neighboring highway.