Boundary condition for soil–atmosphere interfaces in vacuum consolidation modeling

The boundary condition at soil–atmosphere interfaces of vacuum-preloaded soil remains an open issue. Based on a newly developed model that considers the final absolute excess pore-water pressure at the permeable boundary as the original critical air entry value (CAEV), rather than zero as assumed in traditional models, an extended model is proposed in this study accounting for the total stress (i.e., the sum of surcharge, hydrostatic pressure, and self-weight of soil). The determination methods and difference between the original and actual CAEVs are elucidated through the relationships among the void ratio–effective stress ( e– σ′), void ratio–suction ( e– ψ), and void ratio–air entry value ( e–AEV) curves, and the validity of the proposed model is verified via three laboratory tests. It appears that the actual CAEV is greater than the original CAEV, implying a larger final mean effective stress of soil. Their difference magnifies as the total stress increases. Further analysis shows that the subsequent air entry behavior of the inner soil layers differs significantly between the scenarios with an upper and a lower open surface, due to the varying suctions and CAEVs at different soil positions.