One-dimensional consolidation analysis of layered unsaturated soils: An improved model integrating interfacial flow and air contact resistance effects

Layered unsaturated soils exhibit complex mechanical and physical properties. Owing to the roughness between unsaturated soil interfaces and the presence of irregularly distributed micro-pores, this study explores the laminar flow of pore water and counter-cyclonic flow of pore air through these channels at low velocities. In response to the complex consolidation behavior of unsaturated soils influenced by the flow and air contact resistance, an improved model is developed. The model incorporates the flow contact transfer coefficient $\left(R_{\omega }\right)$, flow partition coefficient $\left({\eta }_{\omega }\right)$, air contact transfer coefficient $\left(R_a\right)$ and air partition coefficient $\left({\eta }_a\right)$. Semi-analytical solutions for pore water pressure, pore air pressure and settlement in layered unsaturated soils are derived by employing the Laplace transform and its inverse transform. The rationality of the model is validated through comparative analysis with existing solutions. Analysis of the improved model yields critical insights: the presence of flow and air contact resistance leads to the development of relative pore pressure and air pressure gradients at interfaces, which diminishes the influence of the permeability coefficients of the water phase $\left(k_{\omega }\right)$ and air phase $\left(k_a\right)$ on the consolidation process. Moreover, neglecting the flow and air contact resistance effects may lead to an overestimation of settlement.