Study on the Damage Model of Coal Rock Caused by Hydraulic Pressure and Electrical Impulse in Borehole

Abstract

The purpose of this study is to study the damage and fracturing effects of high-voltage discharge on coal-rock mass under the action of hydrostatic pressure. Based on the traditional damage evolution model and the change of the effective bearing area and stress around the microcrack of coal-rock mass on a microscopic scale, the expression of macroscopic damage variation of coal-rock mass under the action of electrohydraulic coupling was derived, and its damage constitutive relation was established. The high-voltage pulse water shock stress test of coal-rock mass under the conditions of different water pressures and voltages was carried out, and its damage numerical model was established by the ABAQUS/XFEM. The damage variable values of coal-rock mass with different electrohydraulic parameters were compared to characterize the generation and expansion of internal macroscopic cracks. From the results, it is shown that the damage variable based on the effective bearing area and stress around the crack can represent the morphology and expansion change of crack of coal-rock mass with different electrohydraulic parameters clearly and quantitatively. Different hydrostatic pressures and discharge voltages have influence on the damage variables of coal-rock mass, but different influencing degrees cause different damages on coal-rock mass. The damage of coal rock can be characterized by the change of the effective bearing area and stress around microcracks in coal body. So, stress testing and numerical simulation have verified the correctness of the damage model.

Crack Damage Propagation and Morphology Distribution of Hydraulic Electric Pulse Fractured Coal

“…Yin Zhiqiang studied the hydraulic and electrical characteristics of high voltage pulse discharge in water from the theoretical and experimental perspectives and evaluated the cracking effect of coal rock mass. Then Bao Xiankai − used ultrasonic detection technology combined with a variety of advanced numerical simulation software to study the number and CT images to identify and extract cracks in coal core specimens. The parameters such as length, quantity, density, fracture rate, and fractal dimension are further used to quantitatively describe cracks.…”

Investigation on Large-Scale Tests of Rock Fracturing by High-Voltage Electric Pulse with Voltage as a Variable

“…found that a higher breakdown voltage makes the coal body generate more excess pore space, which is more conducive to the extraction of CBM and coal resources . Bao et al found that hydrostatic pressure and voltage affect the effect of HVEPs to fracture coal bodies …”

“…15 Bao et al found that hydrostatic pressure and voltage affect the effect of HVEPs to fracture coal bodies. 16 The working mode of electrical pulses can be classified as electro-fracturing and electro-hydraulic fracturing depending on the medium. 17,18 Electro-fracturing is generated by a direct encounter of the electrode with the material.…”