Moisture infiltration characteristics of capillary barrier covers constructed with PAM-modified quarry waste

To improve the impermeability, water-retention capacity, and ecological suitability of quarry waste covers, an artificial ecological soil was prepared from typical waste rock collected from a quarry in Ezhou, Hubei Province, China. A capillary-barrier cover consisting of coarse and fine soil layers was then constructed, and the fine layer was amended with anionic polyacrylamide (PAM) to enhance its water-holding and seepage- control performance. Indoor soil-column infiltration experiments were conducted to examine the effects of PAM dosage, namely 0% (T1), 0.3% (T2), and 0.6% (T3), on volumetric water content and matric suction at different depths during rainfall infiltration. The results showed that PAM markedly delayed wetting-front migration and increased water storage within the cover layer. At a depth of 7.5 cm, wetting-front arrival times were 0.35 h, 0.59 h, and 1.67 h for T1, T2, and T3, respectively; at 30 cm, the corresponding values were 1.91 h, 3.06 h, and 6.21 h. Distinct water accumulation and backflow occurred at the capillary-barrier interface, where the peak volumetric water content increased from 39.93% in T1 to 46.04% in T2 and 48.53% in T3. Interface breakthrough time also increased with PAM dosage, reaching 4.28 h, 6.81 h, and 13.38 h, respectively. Overall, PAM-modified capillary-barrier covers effectively reduced infiltration and enhanced interfacial water retention, providing a basis for anti-seepage design and ecological restoration of quarry waste cover systems.