Effect of polypropylene fiber on properties of modified magnesium-coal-based solid waste backfill materials

•Through the analysis of slump and rheological test results, the addition of polypropylene fiber reduced the flow performance of modified magnesium-coal-based solid waste backfill materials (MPFB).•Polypropylene fiber reinforced MFPB mechanical properties of late effect is remarkable, early effect is not obvious.•Polypropylene fiber can effectively improve the failure mode of MFPB and enhance the toughness of filling body.•The mechanical properties of polypropylene fiber reinforced MFPB were analyzed from a micro perspective.•The influence of polypropylene fiber on the permeability of MFPB was discussed.