1The Millennium Tower (USA)
The Millennium Tower luxury high-rise opened its doors in 2009 and has since been dubbed "The Leaning Tower of San Francisco." It has sunk about 16 inches and is tilting several inches to the northwest. Developers insist it's still safe for occupancy, and blame its problems on the city's construction of an adjacent railway station, which they say removed groundwater from below and caused it to tilt. In truth, there is no definitive reason as to what caused the lean, but the dispute continues and has spurred numerous lawsuits involving the developer, the city, and owners of its multimillion dollar apartments.
Just recently, the European Space Agency has released detailed data from satellite imagery that shows the skyscraper in San Francisco's financial district is continuing to sink at a steady rate — and perhaps faster than previously known.
Venice is famed for being known as “The Floating City," but that moniker may soon be a thing of the past — the famed destination is sinking more than five times faster than previously thought. The city is also tilting eastward into the Adriatic Sea due to more frequent flooding.
Several measures have been taken to stop Venice from sinking, including the Venice Tide Barrier, and it was believed that the water levels had stabilized. But Scripps Institution of Oceanography at UC San Diego has revealed that the city is still sinking and leaning by an unprecedented 2mm per year over the last decade, with certain northern sections are dropping between 2 to 3mm per year, while the southern lagoon is falling away by 3 to 4mm over the same period.
National Research Council spokesman Luigi Tosi said that Venice's sinking was a combination of land subsidence and sea level rise.
3 Sinking Bell Tower (Philippines)
St. William's Cathedral, in Laoag City, Philippines, is famous for its Sinking Bell Tower. 85 meters away from the church, the 45-meter bell tower was built in 1612 on sandy foundations. It has been slowly sinking into the ground at a rate of about an inch per year. Legend has it that when it was newly built, a person on horseback could enter, but today a person at normal height has to bend just to pass the entrance. Despite this, the bells still ring to call parishioners to mass.
4Palacio de Bellas Artes (Mexico)
Mexico City's Palacio de Bellas Artes has sunk so far that its original ground floor is now a subterranean basement!
The city, built on an island in the middle of a lake around 1325 AD, was plagued by the provision of potable water for centuries. Deforestation depleted springs that had supplied the city with fresh water via aqueducts in the 19th century. The first fresh water well was built in the city center in 1857, and by 1900 there were hundreds of wells sucking water from the underground aquifer.
You can see where this is going.
Some parts of Mexico City have dropped more than seven meters (23 ft) since 1891. Parts of the city center sank more than a meter between 1948 and 1951, and another meter by 1960. The city fell two meters below what remained of Lake Texcoco, posing a serious risk of flooding during the rainy season. In 1950, new wells were drilled south of the city reducing central city sinking to its current rate of about 10 cm (4 in) a year. It helped, but buildings in the southern part of the city began to sink more rapidly.
5Taj Mahal (India)
The Taj Mahal, built more than 350 years ago as a symbol of the Mughal Emperor Shah Jahan's love for his wife, is sinking. One of the minarets of the building has tilted by 3.5 centimeters over the last 30 years.
The ebony foundation of the palace, built on the Yamuna River, requires a steady stream of moisture to maintain stability. Due to climate change, the river now dries up completely during the summer months, causing the breakdown of the foundation and resulting tilt.
6Milwaukee, Wisconsin (USA)
A sizable portion of Milwaukee is sinking.
In the city's Third Ward, the bricks are starting to crumble and crack, and the buildings are beginning to lean. But why?
Much of Milwaukee was built on a marsh. Around the turn of the century, contractors used steam-powered pile drivers to sink into the soggy land below thousands of wood pilings. Concrete was then placed on top of those pilings as a foundation for the buildings to come.
The technique of setting foundations on wood pilings is nothing new and had been used in Europe for centuries, but, "The pilings need to be kept wet. This sounds counter-intuitive, but things that are wet permanently rot slower," UW-Milwaukee Professor of Geosciences Doug Cherkauer said. When the city's water table receded (for reasons that are still unknown), the pilings were exposed to air and — well, you can guess the rest.
7Leaning Tower of Pisa (Italy)
Only 3 meters deep, the foundation of the Leaning Tower of Pisa was built on a dense clay mixture, but clay was not strong enough to hold the building upright. Construction began in 1173, but Pisa started to lean in 1178 when the second floor was added.
The tower is slightly curved from attempts by various architects over the centuries to keep it from leaning more or falling over. In 2008, engineers stated that Pisa had stopped moving, marking the first time in its history that it has not been slowly leaning further to one side. They expect it will remain stable for at least another 200 years. If another intervention is then required, the technology available to make improvements could be far more advanced and preserve the tower for 800 more years. (Tourists, you have plenty of time to post photos of yourself "holding the Tower up " to Instagram. How awesome is that?)
We don't think we'd risk living in any of these buildings in Santos, Brazil — its waterfront is lined with a string of high-rise apartments that are unmistakably tilted to one side.
Below a seven-meter layer of sand is a 30-40 meter thick bed of slippery clay that doesn't cope well with the weight of the structures. Until 1968, local building codes had no restrictions on the type of foundation that could be used for multistory buildings. Ideally, they should reach bedrock, which here is about 50 meters deep, but the buildings on Santos' waterfront have foundations that are only 4 or 5 meters (13 to 16 feet) deep. After the lean in the first building was visible, a requirement was added to the city's building code to deepen the foundation for tall buildings.
Surprisingly, people continue to live in these apartments, and the main problem they face right now is a devaluation of their property — prices of the condos plummeted after the lean became visible to the naked eye many years ago.