Search for: All records

Abstract Granular materials with irregular particle shapes undergo a myriad of temperature variations in natural and engineered systems. However, the impacts of cyclic temperature variations on the mechanics of granular materials remain poorly understood. Specifically, little is known about the response of granular materials to cyclic temperature variations as a function of the following central variables: particle shape, applied stress level, relative density, and temperature amplitude. This paper presents advanced laboratory experiments to explore the impacts of cyclic temperature variations on the mechanics of granular materials, with a focus on sands. The results show that cyclic temperature variations applied to sands induce thermal shakedown: the accumulation of irreversible bulk deformations due to microstructural rearrangements caused by thermal expansions and contractions of the constituting particles. The deformation of sands caused by thermal shakedown strongly depends on particle shape, stress level, relative density, and temperature amplitude. This deformation is limited for individual thermal cycles but accumulates and becomes significant for multiple thermal cycles, leading to substantial compaction in sands and other granular materials, which can affect various natural and engineered systems. 

Abstract Urban areas increasingly suffer from subsurface heat islands: an underground climate change responsible for environmental, public health, and transportation issues. Soils, rocks, and construction materials deform under the influence of temperature variations and excessive deformations can affect the performance of civil infrastructure. Here I explore if ground deformations caused by subsurface heat islands might affect civil infrastructure. The Chicago Loop district is used as a case study. A 3-D computer model informed by data collected via a network of temperature sensors is used to characterize the ground temperature variations, deformations, and displacements caused by underground climate change. These deformations and displacements are significant and, on a case-by-case basis, may be incompatible with the operational requirements of civil structures. Therefore, the impact of underground climate change on civil infrastructure should be considered in future urban planning strategies to avoid possible structural damage and malfunction. Overall, this work suggests that underground climate change can represent a silent hazard for civil infrastructure in the Chicago Loop and other urban areas worldwide, but also an opportunity to reutilize or minimize waste heat in the ground. 

The ground beneath many urban areas worldwide is warming up due to so-called subsurface urban heat islands. Resulting from localized and large-scale drivers of heat in the underground, subsurface heat islands cause thermally induced deformations of key materials constituting civil infrastructure: soils, rocks, concrete, and systems thereof. Currently, the effects of thermally induced deformations driven by subsurface heat islands on the performance and durability of civil infrastructure remain poorly understood. This paper presents the results of a numerical and experimental study to shed light on the impacts of subsurface urban heat islands on civil infrastructure. The study is based on the first 3-D model of the subsurface characterizing the central business district of Chicago, called the Loop, which is affected by an underground climate change. This numerical model is used in combination with temperature data gathered through a sensing network deployed across the Loop district to run thermo-hydro-mechanical simulations of the current subsurface conditions, highlighting satisfactory capabilities to model reality. Based on the analysis of the current subsurface conditions, numerical predictions are run over fifty years to reproduce the influence of heat flows on the deformation of the subsurface. The obtained results indicate that subsurface urban heat islands can involve noteworthy and potentially detrimental effects on the performance and durability of civil infrastructure, requiring consideration in the design of such structures or mitigation through appropriate strategies. An analysis of such strategies is proposed and perspectives to hamper this silent hazard for urban areas are provided.