Hydration-induced microstructure evolution of clay-sulfate rock characterised by X-ray computed tomography

This study examines the swelling behaviour of clay-sulphate rock by observing microstructural changes using X-ray computed tomography (XRCT). Rock swelling presents a significant challenge in geotechnical projects such as tunnelling and road construction, where mineralogical changes can cause considerable structural deformation. This research investigates the microstructural evolution of clay-sulphate rock from the Belchen Tunnel (Switzerland) under different humidity and mechanical conditions. XRCT imaging reveals that water exposure leads to prominent crack formation, mainly along layer interfaces. When exposed to water vapour, gypsum crystals precipitate within cracks and on the rock surfaces, encouraging further crack growth. Conversely, complete submersion in liquid water causes anhydrite to dissolve without subsequent gypsum crystallisation. These results highlight the influence of hydric conditions on the swelling behaviour of clay-sulphate rock and offer valuable microstructural insights for assessing and managing risks in clay-sulphate-rich formations.