Development and engineering validation of environmentally safe coal gangue land reclamation technology based on solidified soil grouting

Land reclamation using coal gangue is an important approach to the large-scale disposal of coal-based solid wastes and the ecological restoration of mining land. However, existing reclamation technologies focus mainly on coal gangue backfilling and soil covering and are inadequate to ensure the structural stability of the backfill, control the risks of spontaneous combustion and heavy metal leaching and release, and support subsequent vegetation restoration. An environmentally safe coal gangue land reclamation technology based on solidified soil grouting is developed, with a focus on the regulation of solidified soil slurry, reconstruction of the internal structure of the coal gangue backfill, and the resulting environmental functions. In situ soil from the mining area is used as the principal material, cement and coal-based solid wastes are used as cementitious materials, and functional admixtures are incorporated to prepare an injectable solidified soil slurry. The prepared slurry is injected through boreholes into the interparticle pores of the coal gangue backfill. After hardening, the slurry is integrated with the gangue skeleton to form a reconstructed solidified soil-coal gangue subsoil layer characterized by pore filling and particle cementation. Functional evaluation of the reconstructed subsoil layer shows that macropores between gangue particles are blocked, thereby impeding continuous oxygen transport. The transition of heated coal gangue from the endothermic stage to the exothermic oxidation stage is also delayed. Oxygen-barrier and flame-retardant functions are thus achieved through restricted oxygen supply and delayed thermal reactions. Meanwhile, the solidified soil filling phase and hydration products reduce contact between infiltrating water and reactive gangue surfaces through interfacial coating, pore blocking, adsorption, and immobilization. Consequently, the migration and release of Pb, As, and Zn are inhibited, and the proportion of labile heavy metal fractions is reduced. During two consecutive years of post-reclamation engineering monitoring, no persistent leachate, spontaneous combustion caused by coal gangue oxidation, or surface soil contamination is observed in the demonstration area. The major monitored groundwater parameters meet the Class Ⅲ groundwater quality limits, the internal temperature of the reconstructed subsoil layer remains below 20 °C, and vegetation on the platform and slopes is restored. The engineering applicability of this technology for large-scale coal gangue disposal, environmental risk control, and vegetation restoration following soil covering is validated by these results. A technical pathway is thereby provided for shifting coal gangue management from stockpiling to functional and environmentally safe land reclamation.