The Leaning Tower of Pisa is one of the most emblematic monuments in Italy. It is not the only structure that leans to one side. The same thing happens with the Dancing Houses of the Netherlands. Or the Tiger Hill Pagoda in China. What is the risk of leaning buildings? Will they fall sooner or later?
There are several reasons why structures lean to one side. In the case of the emblematic Dancing Houses of the Netherlands, it is because of the type of foundation. Most houses are built with wooden stilts. They are installed in pairs under the walls and facades of buildings. They go 12 meters into the soil, which is composed of soft clay, peat or sand.
Other buildings
If they begin to degrade or rot, cracks may appear. Uneven deterioration can cause buildings to lean over time. Soil conditions also play a role. That happens with the emblematic Tower of Pisa. The tower began to lean from the beginning of its construction because the ground is extremely soft. It sank between 3 and 4 meters.
Buildings can also lean due to man-made changes in the ground. For example, the tower of the Oude Kerk, or Old Church, in Delft. It leans more or less in the same way as the Tower of Pisa. It leans towards the canal because the soil on one side was excavated to build it and is softer there.
A leaning building does not necessarily mean that it is not structurally sound. It has to lean quite a bit to be structurally unstable. Sometimes you have to correct the inclinations, as was the case with the Leaning Tower of Pisa. It worsened in the 20th century, with a steady increase in inclination. The chosen technique was earth extraction. Without touching the tower, 37 cubic meters of earth were removed from the north side of the foundation.
Increasing risks
It is also possible to correct a tilt by lifting a house with hydraulic jacks. But it can be harmful. Sometimes the house has adapted to the inclination in a certain way. The risk of leaning buildings increases. In the Netherlands there are around 75,000 houses built on wooden stilts that are at risk of damage. Nearly three times as many are in danger due to shallow foundations. Climate change could make it worse. If the water table drops, the wooden piles are exposed to the air.
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