Abstract
Growing numbers of underground projects have engaged increasingly hostile geothermal environments. Albeit active cooling has become indispensable nowadays for subsurface construction in these challenging settings, the influence of such anthropogenic perturbation on the excavation stability has still remained unclear. A new analytical package is hence developed in this study to explore quantitatively the cooling-induced tunnel response based on thermal–mechanical modeling and local-factor-of-safety (LFS) analysis. By examining the Mohr circle changes pertinent to the spatiotemporal evolution of LFS under different geological and operation schemes, novel insights have thus been obtained into the pivotal control of cooling protocols on the resulting excavation stability. Our analysis has demonstrated that sustained chilling of underground workings could provoke critical switches of principal stress direction, and the excavation stability could thus exhibit a three-phase evolution characterized by initial improvement and ensuing degradation at different rates. In addition, while greater in-situ stress would offset cooling-induced pressure relaxation thereby restraining thermal degradation, the excavation stability could still correlate rather non-monotonically with the ground temperature due to competing effects of tunnel chilling. Moreover, our analysis has also elucidated that albeit employing a manageably higher inner pressure could enhance the stability of deep hydroelectric tunnels throughout, increasing the water head might yet degrade the excavation stability when the geostress is inadequate for restraining circumferential tension during the temperature drawdown. The findings of this study could contribute to better mechanistic insights into the stability of underground workings subject to active cooling protocols, and thus have significant implications for the adaptive excavation design against the increasingly challenging earth environment.