Climate change: The ‘silent hazard’ lurking below buildings

For the first time, a Northwestern study has linked underground climate change to the shifting ground beneath urban areas.

Published in the online Nature Portfolio journal, Communications Engineering, findings from a new, Chicago-based study have outlined that as the ground heats up, it also deforms, creating detrimental effects for the surface in which buildings are constructed upon.

As the ground warms, it causes building foundations and the nearby to move due to expansion and contraction and even forms cracks, which end up causing long-term damage to the structures’ durability.

Researchers have also reported that past building damage could have been caused by such rising temperatures and expect these issues to continue for years to come. According to the Met Office, the average mean temperature of 15.8 degrees that hit England last month, it is the highest on record since 1884. 

‘Underground climate change is a silent hazard’, said Alessandro Rotta Loria, 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.’

To collect data, Rotta Loria and his team set up a wireless network of over 150 temperature sensors across the Chicago Loop, the central business centre of the city, both above and beyond the ground. This involved installing sensors in the basements of buildings, underground parking garages, subway tunnels and subsurface streets.

The data showed that underground temperatures below the Loop are usually 10 degrees celsius warmer than beneath Grant Park, a greenspace area. Once he had this information, which was collected over various years, Rotta Loria built a 3D computer model to simulate how ground temperatures changed since 1951 – the year when Chicago finalised its subway tunnels.

Following this, experts discovered values in line with those measured in the field and used the simulation to predict how temperatures will change until 2051. They also modelled how ground changes in response to higher temperatures. Some materials such as soft clay contract when they experience heat and others such as hard clay ad limestone expand.

‘We have shown that ground deformations can be so severe that they lead to problems for the performance of civil infrastructure,’ Rotta said. ‘It’s not like a building will suddenly collapse. Things are sinking very slowly. The consequences for serviceability of structures and infrastructure can be very bad.’  

Image: Sean Pollock