An analytical model for permeability coefficient of soil-structure interface composed of different capillaries

The soil-structure interface, representing the contact surface between soil and structures such as buildings or rocks, assumes critical importance in water-related projects like earth dams, cut-off walls, side slopes, foundation pits, and water tunnels. Monitoring reports and studies consistently identify this interface as a vulnerable zone susceptible to seepage-related accidents. Despite this recognition, research on the topic has been limited, with a predominant focus on experimental methods that tend to underestimate permeability. This paper presents an analytical model, grounded in capillary theory, for calculating the permeability coefficient of the soil-structure interface. The study explores the differences in permeability between the interfacial soil and far-field soil. The study concludes that the higher porosity of the interfacial soil (porosity ≥ 0.48) compared to the far-field soil (porosity: 0.26–0.48) is a key factor in rendering the soil-structure interface susceptible to seepage. The calculated permeability coefficient of the interface, in relation to experimental values, exhibits a consistent ratio of 2.5–2.6 when the soil porosity is below 0.43, indicating reliable predictive utility. Moreover, the permeability coefficient of the interfacial soil proves to be at least 4.05–6.67 times larger than that of the far-field soil, potentially leading to the creation of preferential seepage channels at the interface.