Startling new information shows Chicago buildings are sinking due to the impacts of a phenomenon known as “underground climate change."
A study conducted by researchers at Chicago’s Northwestern University revealed buildings in the city's Loop are measurably sinking as a result of excessive heat radiated by downtown structures.
The study was published this week in Communications Engineering, and was led by Northwestern Assistant Professor of Civil and Environmental Engineering Alessandro Rotta Loria.
“Underground climate change is a silent hazard,” he said. “The ground is deforming as a result of temperature variations, and no existing civil structure or infrastructure is designed to withstand these variations.”
Loria and his team installed more than 150 temperature sensors around the Loop, in subway tunnels, building basements, parking garages and streets like Lower Wacker Drive.
Sensors were also buried in Grant Park to serve as a comparison tool.
Temperatures in the Loop are often 10 degrees Celsius warmer than underneath Grant Park, and up to 25 degrees higher compared to ground temperatures elsewhere.
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The study is the first of its kind, designed to examine the effects of underground heat on structures that reside in “subsurface heat islands.”
What the study found is that heat is not only diffusing from buildings, but also from underground transportation, thus causing temperatures to rise by up to 2.5 degrees Celsius per decade.
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Such temperature spikes can cause foundations and the surrounding ground to move excessively because of expansions and contractions, which can affect the durability of structures.
Since Chicago is largely built on clay, the city is actually sinking, because clay contracts when it’s heated.
“Many foundations downtown are undergoing unwanted settlement, slowly but continuously. In other words, you don’t need to live in Venice to live in a city that is sinking,” Rotta Loria said.
Warmer temperatures can cause the ground to swell by as much as 12 millimeters, and buildings can sink downward by 8 millimeters, according to the study. That is more than many components and foundations can withstand without compromising their integrity to varying degrees, according to researchers.
Recommendations include installing thermal insulation on new and existing buildings to minimize the output of heat into the surrounding ground.
Researchers also hope that waste heat could someday be recaptured to help mitigate the effects, as well as providing a source of energy.
