Elasticity control through overburden and adsorption competition in porous media

Adsorption-induced deformation is common in porous rocks, but its role in stressed porous rocks remains unclear. These changes in elasticity have critical implications for geological stability, particularly in regions experiencing alternating droughts and wet conditions. This study investigates elastic deformation in fine-grained sandstone under cyclic loading over 34 days, with humidity increased to near dew point. Adsorption-induced weakening decreases from over 40% to less than 10% as overburden pressure rises from 1 MPa to levels below crack initiation. Similar trends are observed in fine-grained granite. A multi-scale model combining contact mechanics and nanopore adsorption explains these results, highlighting stress competition between adsorption effects and overburden pressure. Adsorption weakening becomes negligible beyond burial depths of 200 meters in sandstone and 700 meters in granite. These findings improve understanding of near-surface geological hazards, such as exfoliation, landslides, and cliff failure, under extreme climatic events.