Phase one of San Marco flood barrier underway: soil and archaeological analysis come first

The paving stones (masegni) will be removed in order to inspect the underlying soil in front of the Basilica. Work is projected to last four months, with delays by acqua alte an unknown. The first work site has opened.

By Alberto Vitucci

25 August 2021


The barriers have been installed and work sites are ready. The first operations to lift the paving stones (masegni) to see what lies beneath have begun, the first step in the intervention to defend the Basilica di San Marco. After many ideas and two years of delay, an effort will be made to protect the monument, which has been exposed to years of acqua alta, using glass barriers.

“Job one”, explains site director Giorgio Barbato and the director of the Superintendent of Public Works Francesto Sorrentino, “will be to inspect the condition of the underlying soil, and also to carry out archaeological research”. The paving will be excavated to a depth of two meters, from the piazzetta dei Leoncini to Tretrarchi. It’s delicate work, which will have to establish if there are archaeological discoveries and remains of previous foundations under the ground in front of San Marco. It’s a valid idea that’s of no small concern to the designers. In the case of an important enough discovery – more than possible given the importance of the site – the job site would be closed, causing new delays. The second unknown is the acqua alte themselves. The overlapping delays have led to the work being started on the cusp of the fall season.

It’s unthinkable that the work could be completed in a month. It will take at least four months. Time is needed to do the soil surveys, set the concrete base, and fabricate the steel pillars that will support the glass barriers. Then there will be the finishing work to make the barriers watertight but also openable to allow the installation of walkways in the square.

It’s a simple job, but at the same time complex due to the delicacy of the site.

The cost of the project is 3.5 million Euro, which is not much compared to the enormous sums consumed by MoSE. It seems that the Ministry will pay the expenses after many questions about the legitimacy of using funds for projects outside of MoSE.

The Procuratoria places great hope in the intervention. Yesterday technicians completed various inspections to decide on the following phases of the job. “Finally”, said a happy First Procurator of San Marco, Carlo Alberto Tesserin.

The project, designed by architect Mario Piana and hydraulic engineer Daniele Rinaldo, calls for placing glass barriers – and therefore transparent – in front of the basilica. They will be fixed in the ground at a depth of 70 cm, supported by concrete. They will extend upwards 1 meter, 30 cm. This makes them able to protect the Basilica from tides of up to two meters. It’s a temporary project, destined to be removed when MoSE is put in service and the Piazza is protected by the island project. This larger intervention involves barriers against the entry of water at the four points of contact with the lagoon (Molo, Bacino Orselo, Palazzo Ducale), pumps to remove rain water, and the complete restoration of the underground shafts. Here the cost is 35 million Euro, and in this case as well, the project has been ready for at least a year and a half, having been presented last year at the Biblioteca Marciana by Konstruttiva and Thetis.

Excavation for the glass barriers around the Basilica is about to begin, and within 15 days the technicians will report to the Superintendent. Then the project moves forward. With the hope that this year’s acque alte are milder, seeing that the job site will be active during the peak flood months of October and November, and high tides and floodwater will slow progress.

Last year, left completely defenseless to the tides, the Basilica was flooded almost 200 times, sometimes twice a day.

Source: La Nuova di Venezia e Mestre

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