MSGID: 1:317/3 64ae2c6b   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    The ground is deforming, and buildings aren't ready    
    First study to quantify effects of subsurface climate change on civil   
   infrastructure    
      
     Date:   
         July 11, 2023   
     Source:   
         Northwestern University   
     Summary:   
         A new study has linked underground climate change to the shifting   
         ground beneath urban areas. The phenomenon is affecting all   
         major urban areas around the globe, causing civil structures and   
         infrastructures to crack.   
      
      
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   There is a "silent hazard" lurking underneath our major global cities,   
   and our buildings were not designed to handle it.   
      
   A new Northwestern University study has, for the first time, linked   
   underground climate change to the shifting ground beneath urban areas. As   
   the ground heats up, it also deforms. This phenomenon causes building   
   foundations and the surrounding ground to move excessively (due to   
   expansions and contractions) and even crack, which ultimately affects   
   structures' long-term operational performance and durability. Researchers   
   also report that past building damage may have been caused by such rising   
   temperatures and expect these issues to continue for years to come.   
      
   Although rising temperatures do pose a threat to our infrastructure,   
   the researchers also view it as a potential opportunity. By capturing the   
   waste heat emitted underground from subterranean transportation systems,   
   parking garages and basement facilities, urban planners could mitigate   
   the effects of underground climate change as well as reuse the heat into   
   an untapped thermal energy resource.   
      
   The study will be published on July 11, inCommunications Engineering,   
   a Nature Portfolio journal. It marks the first study to quantify ground   
   deformations caused by subsurface heat islands and their effect on   
   civil infrastructure.   
      
   "Underground climate change is a silent hazard," said Northwestern's   
   Alessandro Rotta Loria, who led 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.   
      
   "Chicago clay can contract when heated, like many other fine-grained   
   soils. As a result of temperature increases underground, 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 -- even if the causes for such phenomena   
   are completely different."  Rotta Loria is an assistant professor of   
   civil and environmental engineering at Northwestern's McCormick School   
   of Engineering.   
      
   What is underground climate change?  In many urban areas around the globe,   
   heat continuously diffuses from buildings and underground transportation,   
   causing the ground to warm at an alarming rate.   
      
   Previous researchers have found that the shallow subsurface beneath   
   cities warms by 0.1 to 2.5 degrees Celsius per decade.   
      
   Known as "underground climate change" or "subsurface heat islands,"   
   this phenomenon has been known to cause ecological issues (such as   
   contaminated ground water) and health issues (including asthma and   
   heatstroke). But, until now, the effect of underground climate change   
   on civil infrastructure has remained unstudied and little 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."  Chicago as a living laboratory   
   In recent years, Rotta Loria and his team installed a wireless network   
   of more than 150 temperature sensors across the Chicago Loop -- both   
   above and below ground. This included placing sensors in the basements   
   of buildings, subway tunnels, underground parking garages and subsurface   
   streets like Lower Wacker Drive. For comparison, the team also buried   
   sensors in Grant Park, a greenspace located along Lake Michigan --   
   away from buildings and underground transportation systems.   
      
   Data from the wireless sensing network indicated that underground   
   temperatures beneath the Loop are often 10 degrees warmer than   
   temperatures beneath Grant Park. Air temperatures in underground   
   structures can be up to 25 degrees higher compared to the undisturbed   
   ground temperature. When the heat diffuses toward the ground, it puts   
   significant stress on materials that expand and contract with changing   
   temperatures.   
      
   "We used Chicago as a living laboratory, but underground climate change is   
   common to nearly all dense urban areas worldwide," Rotta Loria said. "And   
   all urban areas suffering from underground climate change are prone to   
   have problems with infrastructure."  Slowly sinking After collecting   
   temperature data for three years, Rotta Loria built a 3D computer model   
   to simulate how ground temperatures evolved from 1951 (the year Chicago   
   completed its subway tunnels) to today. He found values consistent   
   to those measured in the field and used the simulation to predict how   
   temperatures will evolve until the year 2051.   
      
   Rotta Loria also modeled how ground deforms in response to increasing   
   temperatures. Whereas some materials (soft and stiff clay) contract when   
   heated, other materials (hard clay, sand and limestone) expand.   
      
   According to the simulations, warmer temperatures can cause the ground   
   to swell and expand upward by as much as 12 millimeters. They also can   
   cause the ground to contract and sink downward -- beneath the weight of   
   a building -- by as much as 8 millimeters. Although this seems subtle   
   and is imperceptible to humans, the variation is more than many building   
   components and foundation systems can handle without compromising their   
   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   
   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."   
   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   
   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."   
   The study, "The silent impact of underground climate change on civil   
   infrastructure," was supported by the National Science Foundation (grant   
   number 2046586). The wireless sensing network at the basis of this work,   
   which also serves as a living laboratory for a course taught by Rotta   
   Loria, was partially supported by the Murphy Society and the Alumnae of   
   Northwestern University.   
      
   Video: https://youtu.be/_8IaNoTDxgM   
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   Source: Materials provided by Northwestern_University. Original written   
   by Amanda Morris. Note: Content may be edited for style and length.   
      
      
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   Journal Reference:   
      1. Alessandro F. Rotta Loria. The silent impact of underground climate   
         change on civil infrastructure. Communications Engineering, 2023;   
         2 (1) DOI: 10.1038/s44172-023-00092-1   
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   Link to news story:   
   https://www.sciencedaily.com/releases/2023/07/230711131050.htm   
      
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