Rock interbed containment effect on infiltration processes in purple soil regions

In order to explore the influence of the rock interbed on downward soil moisture infiltration, indoor soil column infiltration experiments were conducted to examine the relationship between 2 different gravel particle sizes (10-20 mm and 20-76 mm) and 5 different gravel contents (0%, 10%, 20%, 30%, and 40%), as well as the cumulative infiltration, infiltration characteristics, and the process of the wetting front. The Horton equation and Philip formula were used to verify the variations in the infiltration characteristics, and the power function was used to simulate the wetting front during the infiltration process. The results showed that: ① The cumulative infiltration becomes smaller with the increase in the rock content of the gravel particles of the same size. For particle sizes between 20 mm and 76 mm, the obstructions to the cumulative infiltration were similar above 20% of the rock content. ② The initial infiltration rate, average infiltration rate, and steady infiltration rate showed an obvious decline, along with the increase of the rock content. The initial infiltration rate of the larger-sized gravel particles is greater than that of the smaller-sized gravel particles. ③ There is a negative correlation between the size of the gravel particle and its obstruction to the wetting front. ④ The Horton equation's validation results of the infiltration characteristics were superior to those derived from the Philip formula; the power function had a good fitting result for the elapsed distance of the wetting front over time in a soil-rock mixture.