Washington D.C., USA, July 19: A recent study conducted by scientists at Northwestern University in Illinois has issued a warning that Downtown Chicago is facing a concerning issue of subsurface heat islands due to underground climate change, which is contributing to the sinking of buildings.
This marks the first time that experts have linked this phenomenon to shifting land beneath urban areas.
The scientists explained that as the ground heats up, layers of clay beneath the surface deform, resulting in excessive movement and even cracking of building foundations and surrounding land. They further emphasized that this could pose a long-term durability challenge for structures.
Importantly, this issue is not limited to Chicago alone, as the study suggests that this “silent hazard” lurks beneath other cities worldwide.
The warming of the ground at an alarming rate is observed in many urban areas, primarily due to the release of heat by buildings and underground transportation systems like subways.
To investigate this, the research team deployed over 150 temperature sensors across the Chicago Loop, the city’s central business district and main downtown section. These sensors were placed both above and below ground, including basements, subway tunnels, underground parking garages, and streets.
Analysis of the collected temperature data revealed that the underground temperatures beneath the Chicago Loop were frequently 10 degrees Celsius warmer than those beneath Grant Park, an adjacent green space devoid of buildings and underground transportation systems.
To gain a comprehensive understanding, the team developed a 3D computer model to examine ground changes from 1951, when the city’s first subway opened, up to the present day. The simulations aligned with the field results and were then employed to predict potential changes by 2051.
According to the study’s predictions, warmer temperatures could lead to ground swelling and upward expansion of up to 12mm, while the weight of a building could cause the ground to sink by 8mm.
Alessandro Rotta Loria, the lead researcher and assistant professor of civil and environmental engineering, referred to this issue as a “silent hazard.”
According to Rotta Loria, there is a phenomenon occurring in downtown Chicago where the clay soil, similar to other fine-grained soils, contracts when exposed to heat. Consequently, numerous foundations in the area are experiencing gradual and continuous settlement. This means that even if the underlying causes differ, living in a city like Chicago can lead to sinking, much like living in Venice.
He added that the consequences for structures and infrastructure could be severe, although they might take a significant amount of time to become apparent.
In light of these findings, Rotta Loria suggested that future urban planners should consider utilizing geothermal technology to harness waste heat and reuse it for building heating purposes.
Loria proposes that integrating thermal insulation into both new and existing constructions offers a viable solution to reduce the infiltration of heat into the ground.
However, he cautions against actively cooling underground structures, as it consumes energy. Currently, there exists a wide range of solutions that can be implemented to address these issues.
The study, shedding light on the slow sinking of buildings in Chicago due to underground climate change, was published in the journal ‘Nature’. The research outcomes underscore the pressing need for proactive measures to address the consequences of rising temperatures beneath urban areas.
