Eco-Compatible Stabilization of Loess Mine Slopes Using a PDADMAC-Based Polymer–Mineral Composite: Hydraulic, Mechanical, and Ecological Performance

Rainfall-induced surface erosion of aeolian loess slopes in open-pit coal mines threatens slope stability and ecological reclamation, whereas conventional rigid protection and ordinary soil stabilizers can hardly reconcile soil reinforcement, impermeabilization, and vegetation compatibility. Here, poly(diallyldimethylammonium chloride) (PDADMAC) was compounded with nano-SiO2, carboxymethyl cellulose, sodium bentonite, and sodium lignosulfonate into a modified PDADMAC-based composite (MPDC). An L18(37) orthogonal array optimized the mix proportion (0.80, 0.50, 0.15, 1.60, and 0.10 wt.% of dry soil for PDADMAC, nano-SiO2, CMC, bentonite, and lignosulfonate, respectively), which was evaluated by shear and permeability tests, scanning electron microscopy, a 480 min rainfall test on a 38° slope model, and six-month field monitoring. The optimum mixture raised cohesion from 18.5 to 41.8 kPa and the friction angle from 26.8° to 32.7°, and cut saturated hydraulic conductivity by 74.3%. Under 480 min of rainfall, sediment loss and erosion ratio were 142.3 g m−2 and 4.7%, i.e., 88.7% and 88.8% below untreated loess, and cumulative infiltration fell by 85.4%. After six months, the treated 0–5 cm layer retained 46.6 kPa cohesion and a 2.2% fissure ratio (versus 20.8%); after 48 h of scouring, soil loss and sliding area were only 5.3 kg m−2 and 1.5 m2 per 100 m2, with Medicago sativa survival above 91.3%. MPDC thus couples soil reinforcement, seepage control, and ecological restoration.