Mechanical and damage behaviors of water-saturated coal samples after adsorption-desorption under different gas pressures based on acoustic emission

Abstract

A thorough investigation into the mechanical properties and damage characteristics of water-saturated coal samples, subsequent to adsorption-desorption under a range of gas pressures, is vital for informing and guiding engineering applications. The TMC uniaxial loading system and acoustic emission (AE) technology were used to study the effects of adsorption-desorption under different gas pressures on the physical-mechanical parameters, failure, and AE of water-saturated coal samples during splitting tests. A new damage constitutive model was established based on AE parameters. The damage evolution of water-saturated coal samples was quantitatively analyzed after adsorption-desorption under different gas pressures, revealing the damage and deterioration mechanisms in water-saturated samples during Brazilian splitting tests. Gas pressure reduced the tensile strength and splitting modulus of coal samples. The damage evolution rate of coal samples underwent an abrupt change at a critical moment, which could be qualitatively evaluated through the peak ringing counts and cumulative energy. The peak cumulative energy of coal samples gradually decreased with the increased gas pressure. The failure mode exhibited significant macroscopic fractures and severe fragmentation. Precursor to destabilization in saturated coal samples was characterized by a synchronous, sharp increase—and in some cases, an order-of-magnitude rise—in cumulative AE energy and cumulative ringing counts. b gradually increased, indicating reduced high-energy events within the sample and a progressive enhancement in the complexity of the microcrack network. According to damage mechanics theory, the damage variable derived from cumulative ringing counts could characterize tensile damage in saturated coal samples. Additionally, a continuous damage model was proposed, using AE ringing counts as a variable. The model described the damage of water-saturated coal samples during deformation failure after adsorption-desorption under different gas pressures. The findings provide a reference for the safe and efficient extraction of pressure-relief gas in high-gas, soft coal seams through hydraulic fracturing.

Keywords

rock mechanics / gas pressure / Brazilian splitting / acoustic emission (AE) / damage constitutive model

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