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Engineers Have Figured Out How the Leaning Tower of Pisa Withstands Earthquakes

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Builders had barely finished the second floor of the Tower of Pisa when the structure started to tilt. Despite foundational issues, the project was completed, and eight centuries and at least four major earthquakes later, the precarious landmark remains standing. Now, a team of engineers from the University of Bristol and other institutions claims to have finally solved the mystery behind its endurance.

Pisa is located between the Arno and Serchio rivers, and the city's iconic tower was built on soft ground consisting largely of clay, shells, and fine sand. The unstable foundation meant the tower had been sinking little by little until 2008, when construction workers removed 70 metric tons of soil to stabilize the site. Today it leans at a 4-degree angle—about 13 feet past perfectly vertical.

Now researchers say that the dirt responsible for the tower's lean also played a vital role in its survival. Their study, which will be presented at this year's European Conference on Earthquake Engineering in Greece, shows that the combination of the tall, stiff tower with the soft soil produced an effect known as dynamic soil-structure interaction, or DSSI. During an earthquake, the tower doesn't move and shake with the earth the same way it would with a firmer, more stable foundation. According to the engineers, the Leaning Tower of Pisa is the world's best example of the effects of DSSI.

"Ironically, the very same soil that caused the leaning instability and brought the tower to the verge of collapse can be credited for helping it survive these seismic events," study co-author George Mylonakis said in a statement.

The tower's earthquake-proof foundation was an accident, but engineers are interested in intentionally incorporating the principles of DSSI into their structures—as long as they can keep them upright at the same time.

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The World’s 10 Most Beautiful Metro Stations
T-Centralen Station in Stockholm, Sweden
T-Centralen Station in Stockholm, Sweden

Some of the most beautiful places on earth lie just below the surface. For proof, look no further than T-Centralen in Stockholm, Sweden, which has just been named the most beautiful metro station in the world by Expedia.

The travel site used Google Trends to analyze the most-mentioned metro stations in the U.S. and Europe, but Expedia ultimately chose the order of its top 10 list and threw in a couple of other hidden gems. Russia and Sweden frequently popped up in their research, so it’s no surprise that stations in those countries secured the top two spots on Expedia's list.

Dubbed “the blue platform,” T-Centralen is the main station of Stockholm’s subway system, and it’s also one of the most ornate. Royal blue flowers and plant patterns creep up cave-like walls, and another section pays tribute to the workers who helped build the Metro. It has been suggested that the color blue was chosen to help commuters feel calmer as they go about their busy days.

A section of T-Centralen
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It was the first station in Sweden to feature artwork, which stemmed from a 1956 competition to decorate the city’s metro stops. Over the years, more than 20 artists have contributed their work to various stations throughout the city, some of which have tackled important social and environmental themes like women’s rights, inclusivity, and deforestation.

In second place is Moscow’s Kosomolskaya Station, which also has an interesting origin story. When the Metro started operating in 1935, it was designed to help promote Soviet propaganda. Kosomolskaya Station, named for workers of the Komsomol youth league who helped build the first Metro line, had marble walls with gilded mosaics, crystal chandeliers, sculptures of fallen leaders, and painted scenes depicting important moments in Russian history. “Unlike the dirty, utilitarian systems of many cities around the world, the Moscow metro drives through a former—but not forgotten—stage of history that sought to bring palaces to the masses,” Expedia’s report states.

Komsomolskaya Station
Komsomolskaya Station in Moscow, Russia

Most of the stations on Expedia’s list are in Europe, but three are in the U.S., including two in New York City and one in Washington, D.C.

Here’s the full top 10 list:

1. T-Centralen Station (Stockholm, Sweden)
2. Kosomolskaya Station (Moscow, Russia)
3. Arts Et Métiers Station (Paris, France)
4. The Wesfriedhof Station (Munich, Germany)
5. Toledo Metro Station (Naples, Italy)
6. Staromestska Station (Prague, Czech Republic)
7. Metro Center Station (Washington, D.C, USA)
8. Mayakovskaya station (Moscow, Russia)
9. Abandoned City Hall Station (New York, USA)
10. New York City’s Grand Central Terminal (New York, USA)

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India's Supreme Court Demands That the Taj Mahal Be Restored or Demolished
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The Taj Mahal is one of the most recognizable monuments on Earth, but over the years it's started to look less like its old self. Smog and insect droppings are staining the once pure-white marble exterior an unseemly shade of yellow. Now, The Art Newspaper reports that India's Supreme Court has set an ultimatum: It's threatening to shut down or demolish the building if it's not restored to its former glory.

Agra, the town where the Taj Mahal is located, has a notorious pollution problem. Automobile traffic, factory smoke, and the open burning of municipal waste have all contributed to the landmark's increasing discoloration. Insects and acid rain also pose a threat to the facade, which is already crumbling away in some parts.

India's highest court now says the country's central government must seek foreign assistance to restore the UNESCO World Heritage Site if it's to remain open. Agra's state of Uttar Pradesh has taken some steps to reduce pollution in recent years, such us banning the burning of cow dung, which produces heavy brown carbon. In 2015, India's Supreme Court ordered all wood-burning crematoriums near the Taj Mahal to be swapped for electric ones.

But the measures haven't done enough to preserve the building. A committee led by the Indian Institute of Technology in Kanpu reportedly plans to investigate the exact sources of pollution in the area, a process that will take about four months. The Supreme Court plans check in on the status of site every day from July 31.

Air pollution isn't the only factor damaging the Taj Mahal. It was constructed near the Yamuna River in the 17th century, and as the water gradual dries up, the ground beneath the structure is shifting. If the trend continues it could lead to the building's total collapse.

[h/t The Art Newspaper]

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