The Sfalassà viaduct: man versus the elements

This monument of Italian civil engineering overlooks the valley of Bagnara Calabra. Suspended at a height of 249 metres (816 feet) over the stream running at the bottom of the valley (it is the second highest viaduct in Italy), and with an amazing Grand Span running for a never-ending 376 metres (1,233 feet), the Sfalassà viaduct floats between the steep mountains of Calabria.

This alone would be enough to make it a monument. But there’s more to the story.

The award-winning design was conceived in 1967 by engineer Silvano Zorzi, one of the leading lights of the 20th century, and it has withstood the test of time so completely that when the Salerno-Reggio Calabria motorway was rebuilt, it started with a simple plan: save the Sfalassà.

Not only was the Sfalassà saved. The new motorway route was designed to incorporate it. This new thoroughfare, built by the Webuild group between 2008 and 2012, included plans to restore this engineering pearl to its former lustre, and together with the construction site of the Favazzina viaduct it proved to be the most complex work of the new Salerno-Reggio Calabria.

It took 1,441 days to build the Sfalassà viaduct and each of them – for those working on the construction site – was a feat.

Strong winds, rainy winters, salt from the sea, steep and crumbly slopes, marshy support structures: the bridge’s builders had to face all this more, and then repeat the experience in 2008 when it was renovated.

The viaduct’s design was unique, because Zorzi solved the problem of these demanding environmental characteristics by adopting the solution of a thrust-bearing arch. In addition to the two 125-meter-high (410-foot-high) piers, the engineer also planned two oblique struts (the largest in the world in terms of size) that unloaded part of the weight of the span onto the mountain slopes. At the time of its inauguration, it was the longest in Europe.

Because of these exceptional technical characteristics, together with the commitment and skills of the workers involved in the construction, the Bagnara bridge won the CECM, Europe’s highest recognition for infrastructure projects, three times, in 1968, 1970 and 1972 — a record at the time.

This also explains why protecting that engineering monument, maintaining it, modernising it and integrating it with the new motorway would soon become a challenge at least as complex as that of its construction.

To the engineers and technicians who were faced with the challenge of latching the viaduct onto the new motorway, it soon became clear that it would be the motorway that would adapt to the Bagnara bridge and not vice versa.

“Our task was to preserve the Sfalassà by modernising it,” says Umberto Cardu today, the technical director of operations of the fifth portion of Salerno-Reggio Calabria, who is also responsible for the work on the bridge. “A complex task precisely because of its unique characteristics.”

Thus work on the new Sfalassà viaduct was divided into three phases, some of which took place at the same time: the first phase was the demolition of the old approaching viaducts that connected the bridge with the motorway, made of reinforced concrete, using a launching girder (to remove the beams) and targeted explosives (to demolish the old piers). The second involved the construction of the new piers to support the new viaducts approaching the Grand Span; and the third and final phase was the launching of the new viaducts, which, due to the characteristics of the foundation, was done inside the new tunnels leading to the Grand Span, or even from the Grand Span itself, towards the new San Giovanni tunnel.

“In essence the entire central body of the Sfalassà (the two central piers 125 meters high, the oblique struts and the span of 376 meters) has remained intact,” said Cardu. “We have rebuilt the ends of the bridge adapting them to the route of the route of the new highway. We were able to achieve this without closing traffic on the carriageway not affected by the works.”

In addition to construction of the new approaching viaducts, however, the bridge’s main span (Grande Span) was also maintained and modernised. “The viaduct had endured over 40 years of traffic and it was necessary to check its condition and upgrade the metal deck, re-doing almost all of the solderings under the direction of the Italian Soldering Institute,” said Cardu. “At the same time, we prepared the metal crossing for its future enlargement.”

These works on the span were accompanied by work on piers 3 and 4, the two giants in reinforced concrete that had been damaged by erosion from the natural elements and needed to be stabilised. “On the piers, we made a new reinforced concrete coat 30 metres (98 feet) high to guarantee the stability of these giants,” says Cardu, adding that the concrete cover of both piers was also re-done.

This series of complex activities had been planned down to the smallest detail. But the real challenge was dealing with the effects of nature.

The sea is just a stone’s throw away, but in winter the peaks of the Aspromonte region become one of the rainiest areas in Italy. Heavy rain, beaten by the wind, soaks the mountains increases the risk of landslides.

“I started sleeping peacefully again only after having completed those works,” Cardu remembers today. “Every rainy night the fear was that a mountain landslide could jeopardise the construction site. I remember on the worst days; some drivers didn’t feel like going down to the bottom with trucks because they were afraid they wouldn’t be able to get back up.” The side facing Salerno was damaged by a large landslide that needed to be remedied by moving nearly 700,000 square meters of earth.

The “battle” for the Sfalassà was also about creating the optimal safety conditions for the people who worked there.

“Part of our job,” continues the technical director, “was dedicated to the construction of the tracks needed to bring the concrete mixers down to the valley, and to stabilising the slopes that otherwise may have collapsed at any moment.”

The environmental protection requirements called for the removal of all the old materials and the re-planting of the slopes with trees and natural vegetation.

“Working on the Sfalassà was one-of-a-kind for its complexity, but to think back on it today, several years later, it was one of the most exciting jobs of my career,” says Cardu. “A constant struggle of man against the elements.”

A struggle conducted with ingenuity and respect, to protect a monument of Italian engineering.