Search

To further elucidate the mechanism of acoustic emission (AE) response when a fractured rock is compressed, a new method for calculating the AE characteristics from the perspective of relative particle motion based on the moment tensor theory in seismology was proposed in discrete element simulation. The crack expansion process and mechanical-deformation characteristics were simulated by the particle flow code (PFC). Based on the new AE response simulation method, the spatial evolution of AE events, magnitude distribution and the orientation of the moment tensor were calculated. The results showed that the stress of the pre-cracked rock under uniaxial compressive conditions drops dramatically after the peak, the cracks expanded rapidly into a macroscopic crack, the acoustic emission events surge, and the brittle damage characteristics after the peak are obvious. The number of tensile and shear cracks obtained from PFC showed a similar growth trend temporally, while the number of tensile cracks was more than that of shear cracks. The acoustic emission magnitudes obtained based on seismology principally concentrated in the range of [−6.9, −5.9], and the slope of the G-R statistical relationship (b value) was 1.81. The spatial orientation of the AE moment tensor coincided with the tensile-shear cracks: the moment tensor is mainly transverse in the wing crack region, with more tensile cracks than shear cracks; while in the main crack region, the moment tensor was heterogeneous, and the percentage of tensile and shear cracks is close to each other. The tensile and shear properties of microcracks were determined based on the T-k diagram and R-value theory of moment tensor. The trends of the percentage of tensile and shear cracks were basically consistent with those obtained by PFC, while the comparison revealed that using [−20, 20] as the interval of tensile-shear crack was more reasonable than that suggested by Feignier et al. The findings provide beneficial reference for accurate analysis of the characteristics of rock cracking seismic sources and the identification of tensile shear properties.

Roadheaders play a vital role in enhancing coal mine production efficiency, but they also generate a significant amount of dust during high-intensity cutting. To address this issue and make dust control more manageable, an approach was developed by adjusting the cutting parameters of the roadheader. This approach is based on analyzing the five stages of dust generation during pick penetrating into the coal, while systematically considering the relationship between the plastic zone volume and the tip angle of the pick. By reducing the angle of the cutting tooth tip and the rotation speed of the cutting head, the amount of dust generated would be decreased. Field experiments were carried out at a tunneling working face to investigate the variations in dust production under different cutting parameters. To control dust at the tunneling working face, a comprehensive dust control method was implemented, including external water spray, a wet dedusting fan, an air curtain, and an inductive full-section water curtain. Dust measurement points were established at the driver of the roadheader, 5 meters behind the roadheader, and 2 meters behind the full-section water curtain to assess the effectiveness of dust control at different locations. The results revealed that replacing the conical picks with a smaller tip angle (92° & 54 rpm) resulted in decrease of average mass concentrations of respirable dust (MRD) and total dust (MTD) with 18.5% and 9.1% lower than the original conditions. Additionally, reducing the cutting head speed (92° & 27 rpm) led to MRD and MTD reductions of 34.5% and 15.8% compared with the original conditions. After implementing comprehensive dust control measures, substantial reductions in MRD and MTD were observed at different locations. At the driver of the roadheader, the average MRD was reduced to 4 mg/m3, with a dust reduction rate of 90.6%. And the average MTD decreased to 20.5 mg/m3, with a dust reduction rate of 93.6%. At 5 meters behind the roadheader, the average MRD and MTD were reduced to 6.6 mg/m3 and 30.1 mg/m3, with dust reduction rates of 86.9% and 91.5%, respectively. At 2 meters behind the water curtain, the average MRD and MTD were reduced to 2.4 mg/m3 and 3.9 mg/m3, with dust reduction rates of 91.3% and 95.1%, respectively. These findings demonstrate the effectiveness of the proposed method in significantly reducing dust generation and ensuring a safer working environment.