Improving seepage characteristics of strongly weathered mudstone slopes with rice husk ash

Strongly weathered mudstone slopes in northern Hebei Province are susceptible to rainfall-induced instability due to their swelling and shrinkage properties. This study investigates rice husk ash (RHA), an agricultural waste byproduct, as an amendment to enhance the seepage characteristics and stability of these slopes. Using pressure plate apparatus and one-dimensional vertical infiltration tests, we examined the effects of varying RHA dosages (0-8%) on water retention, permeability, and wetting front migration. Results show that RHA significantly enhances water retention, reduces unsaturated hydraulic conductivity, and slows wetting front advancement. At a 6% RHA dosage, the wetting front migration time to a 40 cm depth increased to 419 min from 204 min in untreated soil. These improvements stem from RHA's modification of soil pore structure, enhancing impermeability. An optimized Green-Ampt model, incorporating RHA dosage and soil plasticity, accurately predicts infiltration behavior, outperforming the traditional model. This research provides a theoretical basis for using RHA to mitigate rainfall-induced slope instability, offering a practical approach for geotechnical engineering in expansive mudstone regions.