Creep behavior and acoustic emission characteristics of coal samples with different moisture content

Abstract

The acoustic emission (AE) test of step-loaded samples of coal with different moisture contents was conducted using an AG-X250KN rock servo test system and an AE21C AE-monitoring system to study the influence of moisture content on the creep characteristics of coal. The results show that the moisture content influences the creep characteristics of coal samples, in that the greater the moisture content, the greater the creep deformation of the coal and the lower the creep threshold, creep strength, and creep coefficient values. The improved Burgers model can better describe the mechanical properties of creep in coal. In the transient creep stage, the coal micropores and fractures are gradually expanded, and AE activity gradually increased. In the stable creep stage, the creep deformation rate of coal tended to be stable, while new fractures and AE events and energy were all decreased. In the accelerated creep stage, a large number of fractures were generated in the coal, which gradually developed into unstable macrofractures. The stored energy was released rapidly in a relatively short time span, and the number and energy of AE events reached their maximum value. Therefore, the AE characteristics of coal reflect the evolutionary process of damage during creep.

Experiment and Mechanism Investigation on Freezing‐Thawing of Sandstone with Different Water Contents

“…Acoustic emission (AE) activities of rock are mainly caused by the generation, expansion, and fracture of cracks inside the rock and can reveal the damage of the rock [33]. e acoustic emission information of compressed rock contains abundant precursor information of rock failure, which is of great significance for predicting the damage process of rock [34].…”

Creep Damage Evolution of Marble From Acoustic Emission and the Damage Threshold

“…In 1939, Griggs performed creep studies on rock and reported that rock deformation varied with time at a certain stress level (Griggs, 1939). Researchers have made great efforts to perform experiments to analyze features on different kinds of rock, such as granite (Lin et al, 2009;Chen et al, 2015;Xu et al, 2017), shale (Sone and Zoback, 2014), rock salt (Mansouri and Ajalloeian, 2018), sandstone (Brantut et al, 2014b;Chen et al, 2018), limestone (Brantut et al, 2014a;Nicolas et al, 2017), and coal (Ma et al, 2018;Zhang et al, 2019). Additionally, effects of loading history, including single-stage, multi-level loading (Zhao et al, 2017b;Yang et al, 2018), cycle loading and unloading (Chen et al, 2018) were investigated, and numerous researches focused on the temperatures (Xu et al, 2017), water (Liu and Shao, 2017;Yu C. et al, 2019), as well as initial porosity (Brantut et al, 2013).…”

Defining Stress Thresholds of Granite Failure Process Based on Acoustic Emission Activity Parameters

“…AE is directly related to the microfractures in rocks and can be expressed by the damage parameters of rocks. Because the AE signals contain abundant information about crack changes, a number of studies have used AE to investigate the evolution law of crack and rock fracture patterns in Brazilian splitting tests, three-point bending, and compression [11][12][13][14][15][16][17][18][19]. It is found that there are inevitably subjectivity and uncertainty in the process of determining rock deformation by using the crack volume strain method [20][21][22][23][24][25].…”