In order to reveal the effect and rule of hydraulic fracturing by high voltage electric pulse on coal crack

the analysis and the experiment about high voltage electrical hydraulic fracturing was carried out based on the principle of electro-hydraulic effect. Then three specimens were made. In the case of constant hydrostatic pressure at 3 MPa

different voltages（9 kV

11 kV and 13 kV） were applied. The coal samples before and after the experiment were respectively scanned by ultrasonic nondestructive testing techniques to analyze the distribution and expansion of the coal internal cracks

and establish the numerical model to analyze the crack propagation rule and the surrounding stress distribution under experimental conditions. The res

ults showed that the changes of the head ultrasonic wave

'

s time could reflect the change of the crack in the coal sample before and after the experiment. The effect of the pure hydrostatic pressure at 3 MPa on the crack was very slight. While with the increase of the discharge voltage in the water

the new cracks inside the specimen and the density of cracks increased

and the fissure area extended from the central drilling to the edge of the test piece

coal crack effect was obvious. During the loading process

the maximum stress increased gradually and changed with the crack propagation.