Damage mechanism and constitutive model of surface paste disposal of a coal mine collapsed pit in a complicated environment

Abstract

The surface paste disposal (SPD) method can effectively stabilize active coal mine collapsed pits. The degradation mechanism of the mechanical properties of SPD materials in complicated environments has not yet been explored. To investigate the deterioration mechanism of SPD in complicated environments, SPD specimens prepared from coal gangue and a small amount of cement and water as raw materials were tested by freezing-thawing (FT) cycle tests, wetting-drying (WD) cycle tests and freeze-thaw corrosion (FC) tests. The damage evolution law was obtained by the macro- and microscale methods. Studies have shown that the unconfined compressive strength (UCS) of SPD decreases exponentially under FT and FC cycles and decreases linearly after 5 WD cycles. FT, FC and WD all resulted in cracks and holes in SPD. Ettringite (Aft) produced by sulphate corrosion, calcium chloroaluminate hydrate (Friedel's salt) produced by chloride corrosion, magnesium silicate hydrate (M-S-H) produced by magnesium salt corrosion, and thaumasite produced by low temperatures and bicarbonate corrosion are important reasons for SPD strength deterioration. A segmented statistical damage constitutive model with the compaction point as the critical point is established. The damage constitutive model can completely describe the SPD stress-strain curve after corrosion in a complicated environment. The research results can provide guidance for the paste disposal of coal mine collapsed pits.