The spread of subsurface urban heat islands in non-uniform ground

Subsurface urban heat islands (SUHIs) pose a significant yet still insufficiently understood geomechanical risk to urban infrastructure through the development of thermally induced ground deformations and displacements. To date, the numerical studies assessing the impacts of SUHIs on civil infrastructure have relied on simplified ground representations composed of uniform horizontal lithological strata. This convention largely reflects the practical challenges associated with constructing detailed models of the urban subsurface. However, such simplification may fail to capture the complex pathways through which anthropogenic heat propagates in the ground, as well as the interconnected geomechanical response, given that the urban subsurface is typically heterogeneous both vertically and horizontally. This study examines whether this simplification compromises the accuracy of numerical predictions of ground temperatures, strains, and displacements induced by SUHIs. Using the Chicago Loop District as a testbed, we conduct advanced 3D thermo–hydro–mechanical simulations comparing results obtained from simplified stratifications with those derived from more realistic, spatially variable ground models. The findings show that simulations incorporating non-uniform ground conditions produce markedly different temperature fields and substantially larger strains and displacements than those assuming uniform layering. As a result, simplified simulations do not provide conservative evaluations of geomechanical risks caused by SUHIs. An analysis of the relative contribution of individual buried heat sources further reveals that building basements represent the overwhelmingly dominant driver of subsurface temperature anomalies and associated thermally induced deformations. Overall, the results indicate that safeguarding urban infrastructure against SUHIs requires moving beyond simplified ground layering and adopting modeling frameworks that incorporate the true complexity of urban stratigraphy.