For the first time, a new study from Northwestern University has connected underground climate change to the shifting earth beneath urban areas.
The ground stretches as it warms up leading to a phenomenon that results in excessive ground movement and cracking owing to expansions and contractions, which eventually impairs the long-term durability and operational performance of structures.
The researchers claim that such rising temperatures may have contributed to previous building deterioration, and they anticipate that these problems may persist for years to come.
The study which was published in Communications Engineering, a Nature Portfolio journal, quantified ground deformations caused by subsurface heat islands and their impact on civil infrastructure.
“Underground climate change is a silent hazard,” said Alessandro Rotta Loria, an assistant professor of civil and environmental engineering at Northwestern’s McCormick School of Engineering and leader of the study.
“The ground is deforming as a result of temperature variations, and no existing civil structure or infrastructure is designed to withstand these variations. Although this phenomenon is not dangerous for people’s safety necessarily, it will affect the normal day-to-day operations of foundation systems and civil infrastructure at large,” he added.
Underground Climate Change Explained
Urban areas worldwide experience alarming ground warming due to heat diffusion from buildings and underground transportation.
Researchers found that the shallow subsurface beneath cities warms by 0.1 to 2.5 degrees Celsius per decade.
Underground climate change, also known as subsurface heat islands, causes ecological and health issues like contaminated groundwater and asthma.
However, its impact on civil infrastructure remains unstudied and poorly understood.
“If you think about basements, parking garages, tunnels, and trains, all of these facilities continuously emit heat,” Rotta Loria said.
“In general, cities are warmer than rural areas because construction materials periodically trap heat derived from human activity and solar radiation and then release it into the atmosphere. That process has been studied for decades. Now, we are looking at its subsurface counterpart, which is mostly driven by anthropogenic activity,” Rotta added.
The Variations on Chicago Studied
Two researchers, Ferguson and Bayer, who are not part of the study, are monitoring the potential impacts of rising temperatures due to climate change and underground urban development on underground ecosystems.
Groundwater temperature may cause animal deaths, chemical changes, and microbe breeding.
However, the impact of underground hotspots on urban infrastructure remains unexplored.
Rotta Loria suspected heat seeping from basements and tunnels could contribute to wear and tear on structures due to material expansion and contraction with temperature change.
He gathered three-year temperature data from 150 sensors in basements, train tunnels, and parking garages in Chicago’s Loop district.
Sensors were also installed beneath Grant Park in the Loop, near the Lake Michigan shore for comparison purposes.
Chicago’s ground temperatures are rising by 0.25 degrees annually, with underground locations being up to 27 degrees hotter than undisturbed ground.[1]
They also discovered that loop buildings are 10 degrees hotter than Grant Park.
Rotta Loria used a computer model to simulate the underground environment from the 1950s to 2050 and predict future conditions.
The simulations show that warmer temperatures can cause the ground to expand upward by up to 12 millimeters and contract downward by up to 8 millimeters, affecting building components and foundation systems.
This variation is more than most can handle without compromising operational requirements.
“Based on our computer simulations, we have shown that ground deformations can be so severe that they lead to problems for the performance of civil infrastructure,” Rotta Loria said.
“It’s not like a building will suddenly collapse. Things are sinking very slowly. The consequences for the serviceability of structures and infrastructures can be very bad, but it takes a long time to see them. It’s very likely that underground climate change has already caused cracks and excessive foundation settlements that we didn’t associate with this phenomenon because we weren’t aware of it,” he added.
What’s the Best Recourse: Heat Harvesting
Urban planners and architects designed modern buildings before climate change emerged, not allowing for temperature variations like today’s.
Despite this, modern buildings are expected to perform better than earlier structures like the Middle Ages.
As Loria explains, American buildings are relatively new, while European cities with older buildings are more susceptible to subsurface climate change.
He suggests that future planning strategies incorporate geothermal technologies for waste heat harvesting and space heating while installing thermal insulation to minimize ground-level heat entry.
“The most effective and rational approach is to isolate underground structures in a way that the amount of wasted heat is minimal,” Rotta Loria said.
“If this cannot be done, then geothermal technologies offer the opportunity to efficiently absorb and reuse heat in buildings. What we don’t want is to use technologies to actively cool underground structures because that uses energy. Currently, there are a myriad of solutions that can be implemented,” Loria added.
References
- Northwestern Now, ‘The ground is deforming, and buildings aren’t ready’, 11 July 2023, https://news.northwestern.edu/stories/2023/07/the-ground-is-deforming-and-buildings-arent-ready/?fj=1[↩]
