Mechanical Behavior Evolution and Damage Characterization of Coal under Different Cyclic Engineering Loading

Abstract

The cyclic loading causes the strength change of porous rocks, which can be frequently encountered in underground coal mining. In order to quantify the cumulative damage of porous coal, multilevel uniaxial cyclic compressive tests were carried out considering different loading frequencies. The results show that under cyclic loading, Young’s modulus of coal shows a first drastic increase and then decrease trend in terms of the number of loading-unloading cycles, while the Poisson’s ratio gradually increased at lower peak stress amplitudes and then increased sharply with peak cyclic stress amplitude until losing load bearing capacity, following a stepwise rising trend. At a higher loading frequency, volumetric compressibility-dilatancy transition is shifted to an earlier time. The loading/unloading response ratio (LURR) was used to evaluate the damage of coal under cyclic loading. It is found that LURR is an effective parameter to evaluate the damage of coaly rock under cyclic loading and is also useful in distinguishing different deformation mechanism at different loading stages. The results also show that the damage of coal can initiate at the early stage of cyclic loading at a low loading frequency; however, the increase in frequency of cyclic loading can delay the damage time, requiring a relatively higher level of peak cyclic stress amplitude.

Experimental Study on Mechanical Properties of Briquette Coal Samples with Different Moisture Content

“…Although the mechanical properties of briquette and raw coal are not exactly the same, there are great similarities in the mechanical laws of briquette coal [35]. Briquette is favored by many scholars because of its good repeatability [36][37][38][39]. This paper also conducts a series of experiments on briquette coal.…”

Mechanical Properties of Metasandstone under Uniaxial Graded Cyclic Loading and Unloading

“…M. Zhang pointed out that increasing the loading and unloading rate will reduce the total acoustic emission ring of red sandstone samples, and the total acoustic emission count of rock samples has a negative linear relationship with the loading and unloading rate [5]. H. Wang proposed that the loading/unloading response ratio (LURR) can be used to evaluate the damage of coal and rock under cyclic load [6]. T. Wang studied the variation characteristics of acoustic emission energy rate of red sandstone under cyclic loading and unloading.…”

Investigation of the Energy Evolution of Tectonic Coal under Triaxial Cyclic Loading with Different Loading Rates and the Underlying Mechanism

“…The results of these tests have shown that the confining pressure and the amplitude, frequency, and peak value of the axial stress are important factors affecting the mechanical behaviour of rocks [14,26,30]. Wang suggested that the damage time for coal would be delayed by an increase in frequency and that the peak stress of loading had the most significant influence on coal damage [31]. Taheri performed cyclic loading experiments on lignite and observed that, with an increase in confining pressure, the specimen damage under axial loading decreased [32].…”