Dynamic compression mechanical properties of soft coal under different strain rates

The disturbance of deep impact loading can easily induce the instability accident of surrounding rock in soft coal seam. In order to study the dynamic mechanical characteristics of soft coal under different strain rates, aiming at the soft coal of 11518 working face in Panyi Coal Mine of Huainan Mining Area, the cylindrical briquette samples of ø50 mm × 25 mm were pressed. The Split Hopkinson Pressure Bar (SHPB) equipment system was used to carry out the dynamic compression test of coal under five groups of impact velocities (0.30, 0.35, 0.40, 0.45, 0.50 MPa). The dynamic stress-strain curve of coal was obtained, the crushing energy consumption and energy consumption density were calculated, the quality of broken coal in different particle size ranges was screened, and the variation of mechanical characteristic parameters, energy dissipation and crushing characteristics of coal with strain rate were analyzed. The strain rate effect of coal impact failure was revealed. The results show that: In the range of strain rate in test, the initial compaction stage of coal is not obvious, and with the increase of strain rate, the slope of the curve in the elastic deformation stage increases slowly, the yield stage increases, and the drop of stress in the softening stage increases. The peak stress, peak strain and secant modulus of coal increase linearly with the increase of strain rate, with an increase of 130.998 %, 111.335 % and 52.026 %, respectively.With the increase of strain rate, the crushing energy consumption and crushing energy consumption density of coal increase exponentially, and the proportion of crushing energy consumption increases gradually. The larger the strain rate, the more the small volume fragments of coal after failure. In the process of strain rate changing from 66.778 s−1 to 259.154 s−1, the average particle size of the fragments gradually decreased from 3.34 mm to 2.49 mm, and the fractal dimension of the fragments increased slowly from 2.37 to 2.61. The variation trend of crushing characteristics of briquette with strain rate is consistent with that of raw coal (strain rate 57.433−240.100 s−1). The research results can provide experimental basis for clarifying the dynamic mechanical response process of soft coal under impact loading and preventing and controlling instability disasters.