Study on Acoustic Emission Characteristics and Damage Mechanism of Mixed Aggregate Cemented Backfill Under Uniaxial Compression

In order to study the influence of coarse aggregate replacement rates on mechanical properties and damage rules of phosphogypsum (PG) backfill, the uniaxial compression tests of 4 kinds of coarse aggregate replacement rate (40, 50, 60, and 70%) backfill were conducted by YZW-30A rock direct shear instrument and Express-8 acoustic emission (AE) test and analysis system. The results show that with the increase of coarse aggregate content, the negative effect of PG on mechanical strength of backfill decreases, and the compressive strength increases gradually. When coarse aggregate replacement rate is 70%, compressive strength is highest and compressive strength can reach 4.13 MPa. With the increase of coarse aggregate content, the inherent pores in the backfill specimens gradually increase, the deformation of the specimen under uniaxial compression is greater, the specimen shows more cracks, and the AE signal is stronger. Damage constitutive equation and damage evolution equation of the backfill sample can describe the damage evolution characteristics and damage process of the backfill samples, and the trend of theoretical curve agrees with the pater of stress and cumulative ringing count obtained from the experiment. The results have engineering guiding significance for ensuring the safe production in the mined-out area with PG mixed aggregates.