A semi-analytical model for transient infiltration into inclined soil interlayer considering varying water head and stratified water content.

• Influencing factors of infiltration modes were systematically investigated. • A semi-analytical model for three infiltration scenarios was established. • Evolution features of water head and stratified wetting zone were revealed. The classic GA model assumes a constant-head ponded water and with a saturated water content above the wetting zone, which limits its application. This study investigated a semi-analytical method for predicting rainwater infiltration into an inclined soil interlayer considering time-varying head and stratified water content. An evolving wetting profile and a half-parabolic wetting profile of transient zone were observed during infiltration process based on numerical simulations. The water head in the fissure showed a linearly-increasing characteristic before the soil interlayer was fully saturated, while showed an exponentially-increasing feature after the soil interlayer was fully saturated. A semi-analytical model was subsequently established for predicting the variables (time-dependent water head and the length of the stratified wetting zone) based on the classical GA equation, Darcy's law, and mass conversation law, as well as the numerical simulation calibration. This semi-analytical model describes three specific infiltration scenarios (scenarios I, II, and III) involving two infiltration modes (i.e., rainfall infiltration and constant-head infiltration), which were comprehensively shaped by fissure height, rain intensity, and duration. This model has a concise expression satisfying dimensional consistency and can be successfully reduced to the classic GA model. The validity of this semi-empirical model was further confirmed by numerical simulations, which showed good performance by capturing the evolving trends of the water head, saturated, transitional, and wetting zones in the inclined soil interlayer. The results and findings deepen the understanding of transient infiltration in rock slopes with inclined soil interlayer, and are helpfully for assessing the evolving slope stability during rainfall. [ABSTRACT FROM AUTHOR]