Study on strength and deformation characteristics of cemented gangue backfill body under the coupling action of load and salt erosion

•Within 50 % stress-strength ratio has an inhibitory effect on the erosion of the CGBB.•The erosion products increased the compactness of CGBB in the early stage, and worsen the structure of CGBB in the later stage.•Established a strain gauge-ultrasonic-resistivity composite monitoring system to monitor damage changes during erosion.•A certain compressive stress could slow down the erosion mechanism of CGBB. The durability of backfill body is very important to maintain the stability of goaf. To explore the long-term strength and deformation characteristics of backfill body under the coupling action of load and salt erosion, the cemented gangue backfill body (CGBB) under different compressive stress levels was eroded in MgSO4 solution for 210 days. The ultrasonic and resistivity changes of CGBB at different ages were monitored and the microstructure of CGBB was analyzed by scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and X-ray diffraction (XRD). The results showed that the compressive strength of CGBB increased with the rise of compressive stress level, and the compressive strength of the eroded specimens was less than that of the not eroded specimens. The deformation of CGBB increased with the increase of time and compressive stress level, and there was still a certain increase in the later deformation of the eroded CGBB. The ultrasonic pulse velocity (UPV) of eroded CGBB can be divided into three stages: rapid growth, slow growth and gradual decrease. The resistivity of the eroded CGBB decreased rapidly in the early stage, and then increases slowly. The greater the compressive stress is, the smaller the growth rate is. By analyzing microstructure, the formation of expansion products changed the compactness of CGBB in different erosion stages, and the compressive stress within 50 % stress-strength ratio inhibited the erosion of CGBB. The research results can provide reference for the design of backfill body.