An Interfacial Flow Contact Model for Axisymmetric Consolidation Analysis of Unsaturated‐Saturated Soils Under Continuous Drainage Boundaries

ABSTRACT The tortuous morphology of fluid channels and inherent fluid viscosity cause significant friction and air resistance at the unsaturated‐saturated soil interface. This resistance significantly reduces fluid seepage velocity, leading to an interfacial flow contact resistance effect. To address this, a flow contact transfer coefficient () and a flow partition coefficient () are introduced to establish a general imperfect flow contact model. This model quantitatively describes the resistance encountered by pore water as it seeps across interface channels. Based on this model, semi‐analytical solutions for pore water pressure, pore air pressure, and foundation settlement of unsaturated‐saturated soil foundations with vertical drains under continuous drainage conditions are derived by employing the Laplace transform and the finite Hankel transform. The consolidation behavior of foundations improved by vertical drains is then systematically investigated. Results indicate that the interfacial flow contact resistance effect significantly impedes pore water discharge, inducing a maximum pore water pressure gradient of 32.2 kPa at the interface. Compared with the complete flow contact model, the proposed model exhibits significant consolidation retardation. Specifically, at a depth of 8m, the initial dissipation of pore water pressure is delayed by approximately 11.1 h, and the complete dissipation period is extended by 46.29 days. Furthermore, under weak radial drainage conditions, the time required to reach a settlement of 183 mm is delayed by approximately 69 days.