The O’Hare International Airport subway station in Chicago, Illinois is relatively new and opened in 1984. Chicago Transit Authority
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Climate change causing worldwide temperatures to rise, leading droughts, heat waves And Forest fires. It warms the surface of the ocean, intensifying hurricanes and increasing acidity And ecosystem imbalances.
But the climate crisis is also happening under our feet, in a phenomenon called “underground climate change”.
The concept has been studied for years around the problems of railway tracks buckling in the heat and groundwater contaminationaccording to CNN.
However, it is only recently, in a new study by Alessandro F. Rotta Loria, assistant professor of civil and environmental engineering at Northwestern University, that the effects of underground climate change – also known as “underground heat islands” – on civil infrastructure have been examined, a press release from Northwestern University said.
“Underground climate change is a silent danger,” Rotta said Loria in the press release. “The ground deforms under the effect of temperature variations, and no existing civil structure or infrastructure is designed to withstand these variations. Although this phenomenon is not necessarily dangerous for the safety of people, it will affect the normal day-to-day operations of foundation systems and civil infrastructure in general.
The study, “The Silent Impact of Underground Climate Change on Civil Infrastructure,” was published in the journal Communications Engineering.
As the ground gets warmer, it can expand, contract and deform, causing the foundations of buildings to shift and sometimes crack. This can affect the strength and performance of structures.
“Chicago clay can contract when heated, like many other fine-grained soils. Due to rising temperatures underground, many downtown foundations are experiencing slow, but continuous, unwanted settlement. In other words, you don’t have to live in Venice to live in a collapsing city, even though the causes of such phenomena are completely different,” Rotta said. Loria said.
Previous research found a warming of 0.1 to 2.5 degrees Celsius every decade for the subsoil of cities.
“If you think of basements, parking lots, tunnels and trains, all of these facilities are continuously emitting heat,” Rotta said. Loria said in the press release. “In general, cities are warmer than rural areas because building materials periodically trap heat derived from human activity and solar radiation and then release it into the atmosphere. This process has been studied for decades. Now we take a look at its subterranean counterpart, which is driven primarily by human activity.
Rotta Loria and the research team installed more than 150 wireless temperature sensors above and below ground along the Chicago Loop. The researchers placed them in subway tunnels, basements, underground streets and underground parking lots. They also buried some in Grant Park for comparison.
The team found that temperatures under the Chicago Loop were often 10 degrees Celsius higher than those under Grant Park.
Underground air temperature can be up to 25 degrees Celsius higher than the temperature of intact ground, which can lead to warping, cracking and heat stroke problems for people using the structures.
“We used Chicago as a living laboratory, but underground climate change is common to almost every dense urban area in the world. And all urban areas suffering from underground climate change are likely to have infrastructure problems,” Rotta Loria said.
Rotta Loria made a 3D computer model after three years of temperature data collection that was able to simulate the evolution of underground temperatures since 1951 – the year the city completed its subway tunnels. The values were comparable to field data, so Rotta Loria used them to predict the evolution of temperatures until 2051.
Rotta Loria also proposed a model of soil deformation in response to rising temperatures. Materials such as hard and soft clay contract when heated, while materials such as limestone and hard clay expand.
Simulations have shown that warmer temperatures can lead to soil expansion and swelling of up to 12 millimeters. Rising temperatures can also cause the ground to contract and sag under the weight of a building by up to eight millimeters. It may not seem like much, but it’s more than many foundations and building components can support and function.
“Based on our computer simulations, we have shown that ground deformations can be so severe that they lead to performance issues in civil infrastructure,” Rotta Loria said in the press release. “It’s not like a building is suddenly going to collapse. Things are flowing very slowly. The consequences on the working condition of structures and infrastructure can be very bad, but it takes a long time to see them. It is very likely that underground climate change has already caused excessive cracking and settlement of the foundations which we have not associated with this phenomenon because we were not aware of it.
Rotta Loria pointed out that new buildings fare better than old ones.
“In the United States, the buildings are all relatively new. European cities with very old buildings will be more susceptible to underground climate change. Stone and brick buildings that employ past design and construction practices are usually in a very delicate balance with the disruptions associated with the functioning of cities today. Thermal disturbances related to underground heat islands can have detrimental impacts for such constructions,” said Rotta Loria.
Rotta Loria pointed out that building planners can minimize the amount of heat that enters the ground by installing thermal insulation.
“The most efficient and rational approach is to insulate underground structures in such a way that the amount of heat lost is minimal,” Rotta Loria said in the press release. “If this cannot be done, then geothermal technologies offer the possibility of effectively absorbing and reusing heat in buildings. What we don’t want is to use technologies to actively cool underground structures, because that consumes energy. Currently, there are a myriad of solutions that can be implemented.