Fracture behavior and acoustic emission characteristics of sandstone samples with inclined precracks

Sandstone samples with precracks of different dip angles were collected from a coal mine roof and subjected to uniaxial compression tests, and acoustic emission (AE) and scanning electron microscopy (SEM) were used to study how the crack dip angle affected the fracture mechanism. In the precracked sandstone samples, as the dip angle between the crack line and loading direction decreased, so did the peak stress and its completion time. The SEM observations revealed a fracture transition from tensile cleavage to shear slip, which was manifested by a microstructure change from aggregate to staggered. According to energy conversion, a decreased crack dip angle results in gradually decreasing total and dissipative peak energies, whose variation amplitudes at different stages are consistent with those of the peak stress of the samples. The decreased crack dip angle lowered the stress required to trigger the first appearance of AE energy peaks and ring-down counts, as well as shortening the period before the occurrence of the first AE peak signal. However, the AE energy and ring-down count during the failure stage after the stress peak increased gradually. A stepped increase was observed in the AE ring-down count curves, with each step corresponding to a jump in the stress-strain curve. From the characteristics of the AE signal of the fracture of a precracked rock sample, the occurrence of joints or faults in the rock mass can be reasonably inferred. This is expected to provide a new method and approach for predicting coal and rock dynamic disasters.

Automated summary

The research shows that a smaller crack dip angle can reduce peak stress and completion time, as well as induce a transition in the fracture mechanism. Changes in crack dip angle affect total and dissipative peak energies, while the appearance time of AE signals is also shortened.