Stabilization of forest road subgrades with lime and wood ash: A sustainable approach to enhancing durability and reducing soil erosion under freeze–thaw cycles

• Evaluated lime (5%) and wood ash (10%) stabilization on silty clay subgrades under freeze–thaw cycles. • Significantly improved soil strength and durability (UCS, CBR, IPI, FDI, ERI). • Reduced road-scale erosion from 4.15 to 2.14–2.40 t/km/cycle, with an average reduction of 36% across all cycles. • SEM and XRD confirmed pozzolanic reactions and microstructural densification. • Economic analysis indicated annual savings of $419–433/km attributable solely to reduced road-surface erosion. Forest road subgrades in mountainous regions are highly vulnerable to erosion and structural deterioration under seasonal freeze–thaw (F–T) cycles. This study aimed to (i) evaluate the effects of lime (5%) and wood ash (10%) as stabilizing agents on the mechanical strength and durability of subgrade soils (silty clay) subjected to F–T cycles, and (ii) assess their influence on soil erosion and the associated annual benefits of erosion reduction. Soil mixtures containing different stabilizers were prepared and subjected to 0, 5, 10, and 15 F–T cycles in the laboratory, followed by mechanical, structural, and mineralogical characterization. In addition, several composite and technical indices related to soil erosion from the forest road body were calculated, alongside road-scale erosion measurements. The results indicated that all stabilized soils exhibited enhanced strength and durability. The incorporation of lime and bamboo ash increased the unconfined compressive strength (UCS) by 41.6% after 15 freeze–thaw cycles, improved weight loss resistance by 29.4%, and increased the California Bearing Ratio (CBR) by approximately 35% compared with the degraded control sample. SEM and XRD analyses revealed cohesive gel formation and stronger interparticle bonding, mitigating structural degradation under repeated F–T cycles. Overall engineering performance was markedly enhanced, with the soil–lime–bamboo treatment achieving the highest performance index (IPI ≈ 63), representing a 76% improvement over untreated soil. On average, treated soils reduced erosion by around 36%, and lime-ash stabilization significantly lowered road-scale erosion from 4.15 to 2.14 t/km/cycle, demonstrating both environmental and economic benefits. Economic analysis further highlighted annual savings of roughly $430 per 1-km road segment, corresponding to about 12% of maintenance costs. These findings provide strong technical and environmental justification for lime and lime–wood ash stabilization. Bamboo ash mixtures emerge as the most effective and sustainable option for forest road construction in cold regions, while lime-only stabilization remains a practical and cost-efficient alternative.