Experimental Investigation of Mechanical Behavior and Damage Evolution of Coal Materials Subjected to Cyclic Triaxial Loads with Increasing Amplitudes

TL;DR

This paper studies how coal behaves under increasing cyclic loads, revealing how stress affects deformation and damage in mining roadways.

Contribution

A new damage evolution model is proposed that accounts for both initial and load-induced coal damage under cyclic triaxial loading.

Findings

Peak deviatoric stress and axial residual strain increase with higher confining pressures.

Coal specimens fail via shear with local tensile cracks near shear bands.

The proposed damage model captures deformation and failure under cyclic loads.

Abstract

As a part of the mining-induced stress redistribution process during coal mining, the repeated loading and unloading process with increasing peak stresses will cause more severe deformation and damage to mining roadways, which is different from the findings in other underground engineering practices. Consequently, cyclic triaxial compression tests with increasing amplitudes were carried out to investigate the mechanical behavior, acoustic emission (AE) characteristics, and damage evolution of coal materials. It is found that peak deviatoric stress and axial residual strain at the failure of coal specimens increase with increasing confining pressures, while the changes in circumferential strain are not obvious. Moreover, the failure patterns of coal specimens exhibit shear failure due to the constraint of confining pressures while some local tensile cracks occur near the shear bands at both ends of the specimens. After that, the damage evolution of coal specimens was analyzed against the regularity of AE counts and energies to develop a damage evolution model. It is concluded that the damage evolution model can not only quantify the deformation and failure process of the coal specimens under cyclic loads with increasing amplitudes but also takes into account both the initial damage due to natural defects and the induced damage by the cyclic loads in previous cycles.

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