In construction, deep foundations are used when the ground does not have sufficient bearing capacity to support a building. This special type of foundation solves this problem by driving a column or pillar into the ground until it reaches firmer layers at greater depths. A particularly unique example of this type of construction is found in Venice, Italy.
In fact, the oldest buildings in that city are supported by wooden piles. However, their proper functioning is due in part to their massive use, with thousands of them under the floors of these buildings. Therefore, the piles improve the surface ground conditions and form the solid and stable support platform that sustains the city. It is estimated that there are around 12,000 piles supporting the Rialto Bridge, for example, while the Basilica of Santa Maria della Salute rests on more than a million.
Wood of varying quality was used in the construction of buildings in Venice, partly as a result of the economic capacity of each project. The most common types were alder, oak, larch, pine and elm. The space between the piles was filled with gravel and crushed stone. Istrian stone slabs were laid on the resulting platform, which served as the foundation for the buildings.
But why don’t the wooden piles rot? The explanation lies in a combination of several factors. Firstly, the water in the lagoon has a high salinity level due to the constant inflow of seawater, which prevents the growth of many fungi and bacteria responsible for wood degradation. Likewise, the lack of oxygen in these waters hinders the proliferation of these microorganisms. In addition, over time, minerals dissolved in the water and sediment penetrate the wood and cause its partial mineralisation, therefore hardening and stabilising it.
The effectiveness of this system was demonstrated when, after the collapse of St. Mark’s Campanile in 1902, it was discovered that its original piles, after almost a thousand years of service, were still in very good condition.
By Jorge Laguna, head of the structures section of the Architecture Department at Amusement Logic.
Photo by Ricardo Gomez Angel in Unsplash
