Failure behaviour and acoustic emission characteristics of different rocks under uniaxial compression

In the present study, mechanical behaviour of three types of rocks has been investigated under uniaxial compression. The stress-strain responses of the tested rocks are composed of four regions: the compaction stage; elastic stage; strain hardening stage and strain softening stage. The elastic modulus and uniaxial compressive strength increase in order from the result of the coal to the mudstone and then to the sandstone, while the Poisson ratio shows a reverse order. In coal and mudstone, volumetric dilation behaviour vanishes gradually with an increase in damage degree, while it remains stable in the sandstone where the strain hardening behaviour is less obvious. Regarding acoustic emission (AE) characteristics, AE hit and AE energy show a similar evolutionary trend in the loading process. A sudden increase in AE energy is accompanied with drastic drop or local fluctuation in the load-bearing capacity of the rock while AE hit fails in predicting such variation in the load-bearing capacity. A quiet stage of AE signal prior to the peak stress is captured, which can be taken as a precursor for rock failure. Failure pattern of the coal, mudstone and sandstone varies from shear faulting to tension-shear mixed fracturing and then to axial splitting, which is in good accordance with that deduced from AE location analysis.