Infiltration resistance of hydrophobic soil slopes under extreme rainfall: centrifuge model tests

The increasing frequency of extreme rainfall necessitates slope protection methods that directly regulate infiltration. This study proposes engineered hydrophobicity as a delay-based infiltration control mechanism. Centrifuge model tests were conducted to evaluate slopes containing hydrophobically treated soil layers under prototype-scale rainfall (90 mm/h). Compared to untreated slopes, the hydrophobic layers delayed wetting-front progression and pore-water pressure buildup. Although thicker hydrophobic layers increased infiltration delay, they also reduced post-rainfall drainage efficiency and promoted water accumulation near the lower slope. Comparative tests using silica sand and recycled fine aggregates demonstrated the applicability of the method to different soil types, with recycled materials providing comparable resistance. These results indicate that engineered hydrophobic soils can function as delay-based infiltration-control layers under extreme rainfall conditions.