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Underground Climate Change: A Silent Hazard

Discover the startling reality as major U.S. East Coast cities experience accelerated subsidence, posing severe threats to infrastructure and communities.

As underground temperatures rise, the ground undergoes deformation, leading to excessive movement and cracking in building foundations and the surrounding soil. This is the “silent hazard” lurking underneath major global cities, and the buildings are not designed to handle it, according to a study.

The phenomenon poses significant challenges to the long-term performance and durability of structures, the researchers at the University said.

The research also suggests that past instances of building damage may have been caused by rising temperatures, and these issues are expected to persist in the coming years.

POTENTIAL OPPORTUNITY

While rising temperatures pose a threat to infrastructure, the study identifies it as a potential opportunity as well. By capturing and utilizing the waste heat emitted from subterranean transportation systems, parking garages, and basement facilities, urban planners can mitigate the effects of underground climate change while also tapping into an untapped thermal energy resource.

SILENT HAZARD

Lead researcher Alessandro Rotta Loria, an assistant professor of civil and environmental engineering at Northwester’s McCormick School of Engineering, describes underground climate change as a “silent hazard” that affects the normal operations of foundation systems and infrastructure in cities worldwide.

Underground climate change refers to the phenomenon of heat diffusing from buildings and underground transportation systems, causing the ground to warm at an alarming rate. Previous studies have shown that the shallow subsurface beneath cities can warm by 0.1 to 2.5 degrees Celsius per decade.

METHOD AND FINDINGS

In this research, North-western University installed a wireless network of over 150 temperature sensors across Chicago’s Loop, including buildings’ basements, subway tunnels, underground parking garages, and subsurface streets like Lower Wacker Drive. The data collected revealed that temperatures beneath the Loop were often 10 degrees Celsius higher than temperatures beneath Grant Park, a green space away from buildings and underground transportation systems. The study found that air temperatures in underground structures could be up to 25 degrees higher than the undisturbed ground temperature.

Rotta Loria developed a 3D computer model to simulate ground temperature changes from 1951 to the present, which confirmed values consistent with field measurements. The model also demonstrated the potential for ground deformation due to increasing temperatures. While some materials contract when heated, others expand, leading to ground swelling or sinking. The simulations revealed that the ground could expand upward by up to 12 millimetres or sink downward by up to 8 millimetres, posing challenges for infrastructure performance over time.

ACTION

The study emphasizes the need for immediate action to address the impacts of underground climate change on infrastructure. Rotta Loria suggests integrating geothermal technologies into future planning strategies to harness waste heat and provide space heating in buildings. Additionally, thermal insulation can be installed in both new and existing structures to minimize heat transfer to the ground.

The findings shed light on the necessity of adapting urban planning and construction practices to account for underground climate change. While newer buildings are better equipped to handle temperature variations, historical structures, especially those made of stone and bricks, may be more vulnerable. The study emphasizes the importance of minimizing wasted heat through insulation and utilizing geothermal technologies to effectively manage underground climate change.

HARVESTING HEAT

Because urban planners and architects designed most modern buildings before underground climate change emerged, they did not design structures to tolerate the temperature variations we experience today. Still, modern buildings will fare better than structures from earlier time periods, such as the Middle Ages.

“In the United States, the buildings are all relatively new,” Rotta Loria said. “European cities with very old buildings will be more susceptible to subsurface climate change. Buildings made of stone and bricks that resort to past design and construction practices are generally in a very delicate equilibrium with the perturbations associated with the current operations of cities. The thermal perturbations linked to subsurface heat islands can have detrimental impacts for such constructions.”

Going forward, Rotta Loria said future planning strategies should integrate geothermal technologies to harvest waste heat and deliver it to buildings for space heating. Planners also can install thermal insulation on new and existing buildings to minimize the amount of heat that enters the ground.

“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 do not 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.”

WHAT IS UNDERGROUND CLIMATE CHANGE?

Underground climate change is the change in temperature and other climatic factors in the underground environment. A number of factors, including, causes it:

  • Urbanization: The construction of underground structures, such as tunnels, basements, and parking garages, can trap heat and cause the underground temperature to rise.
  • Groundwater extraction: The extraction of groundwater can lower the water table, which can lead to the oxidation of organic matter and the release of heat.
  • Climate change: Climate change is causing the Earth’s atmosphere to warm, and this warming is also affecting the underground environment.

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