Compaction behaviour and sensitivity analysis of crushed gangue-waste backfill material under stress-seepage coupling

By crushing and screening gangue, the crushed gangue-waste backfill material (CGWBM) can be prepared for backfilling the underground gob, which facilitates the proper disposal of gangue solid waste and effective control of overburden deformation, failure and surface subsidence. In underground environments, the CGWBM is subject to the combined effects of in-situ stress and seepage pressure, and its compaction deformation characteristics remain unclear. In this study, a stress-seepage effect testing system for backfill materials was developed, and the deformation response of CGWBM samples with different particle size distributions (PSDs) under the coupled field of the axial stress and seepage pressure was explored. Results indicate that the seepage effect plays a critical role in determining the sample’s stability by altering its particle arrangement structure. The samples with a PSD of 0–5 mm and 15–20 mm still contain numerous voids under stress, exhibiting poor resistance to seepage. The application of axial stress can stabilise the sample structure and enhance its seepage resistance. The sensitivity analysis reveals that the PSD of CGWBM samples is the main controlling factor for their compaction characteristics. This study lays the groundwork for the PSD optimisation of the CGWBM and the control of rock strata.