Effect of wet-dry cycle on triaxial mechanical properties and constitutive models of solid waste cemented backfill

As the environmental requirements of underground mine backfilling processes have been promoted, solid waste cemented backfilling (SWCB) technology is widely exploited in goaf backfilling. Due to the groundwater circulation and geothermal drying effects, the SWCB is often exposed to the cycle period of wetting and drying state. To study the influence of wet -dry state transformation on the mechanical properties of SWCB, a series of triaxial compression tests were carried out on SWCB specimens treated with wet -dry cycle. As the cycle numbers increased, first, mass-loss behavior occurred and then hydration damage gradually accumulated in the SWCB specimen, where the maximum mass loss rate (Rw-d) was 7 %. The triaxial compressive strength (TCS) and elastic modulus of SWCB increased with the increase in confining pressure but decreased with the increase in cycle numbers. In low cycle numbers, the wet -dry cycle treatment did not damage the skeleton structure, and the SWCB specimen could still bear external load after failure. A constitutive model considering residual strength was established to describe the stress state and failure process of SWCB specimens. In high cycle numbers, hydration damage occurred and was widely distributed in the SWCB specimen. A rheology constitutive model was established to reflect the stress-strain relationship and flow failure characteristic. From the scanning electron microscopy (SEM) results after SWCB specimen failure, main cracks and many partial microcracks appeared in the low and high cycle numbers, which verified the applicability for two constitutive models. Aiming at the negative effect of wet -dry cycle on the mechanical properties of SWCB, isolating water source and protecting SWCB were proposed to prevent and control the large deformation of SWCB and surface subsidence induced by rheological behavior.