Fig 1.
The determination of ultrasonic parameters (modified from [34]).
Fig 2.
Test flowchart.
Fig 3.
Test system and sample.
Table 1.
The mechanical and ultrasonic testing results of coal and rock bodies around boreholes.
Fig 4.
The sketches of the failure form and the cloud images of strain field.
Fig 5.
Initial ultrasonic amplitude of samples.
Fig 6.
Ultrasonic waveform of coal and rock bodies around boreholes during progressive failure.
Fig 7.
Initial ultrasonic velocity of samples.
Fig 8.
Ultrasonic velocity of coal and rock bodies around boreholes during progressive failure.
Fig 9.
Ultrasonic attenuation of coal and rock bodies around boreholes during progressive failure.
Fig 10.
Equivalent crack width model of the sample.
Fig 11.
Equivalent crack width evolution curve of the sample during progressive failure.