An Experimental Study Into the Effects of Cumulative Energy Damage on the Mechanical Properties of Coal

Shuai Guo,A.J.S (Sam) Spearing,Zhaojun Wang,Peng Huang,Xiangjian Dong

doi:10.3389/fmats.2021.733391

Abstract

The accumulated damage of the surrounding rocks induced by the existing coal mining activities (such as excavation and extraction) is the initial mechanical background of the rock and coal for the further mining operations. An energy-based Cumulative Initial Damage (CID) variable was proposed to account for such existing damage. With the MTS815 electro-hydraulic servo-controlled system, coal samples with different CID value were prepared by cyclic pre-loading and unloading process, and a novel experimental framework was presented to investigate the effect of CID on the further mechanical properties of the CID coal samples. The deformation characteristics, peak strength, peak strain, dilatancy characteristics, brittle-ductile transformation behavior, and microscopic structure of the CID coal samples were investigated in detail. The triaxial compression tests showed that with the increased of CID value, the compaction part of the coal samples was shorter and the strain softening stage became longer. When the CID value was increased from 0 to 0.521, the deviation stress and peak strain of the coal decreased by 31.4 and 37.7%, respectively and the main characteristic of the fracture morphology changed from cleavage steps to dimpling.

Highlights

In recent years, many studies have focused on the mechanical characteristics of coal and rock medium generally, as they have a substantial influence on the stability and safety of underground excavations and in some conditions could contribute to understand and eliminate serious mine disaster
The damage variable increases with the increase of loading and unloading times, which indicates that the number of times of cyclic loading can increase the degree of damage, which agrees with the basic properties of rock mechanics
With the MTS815 electro-hydraulic servo-controlled loading system, coal samples with various Cumulative Initial Damage (CID) value were prepared by cyclic pre-loading and unloading and the mechanical behavior of these prefabricated CID coal samples, including deformation characteristics, strength, peak strain, dilatancy characteristics and brittle-ductile transformation, was investigated

Summary

Introduction

Many studies have focused on the mechanical characteristics of coal and rock medium generally, as they have a substantial influence on the stability and safety of underground excavations and in some conditions could contribute to understand and eliminate serious mine disaster. The terminology of Cumulative Initial Damage (CID) in this study is defined as the damage accumulated in the rock and coal mass by the former mining activities (Jiang et al, 2019). During the subsequent mining activities, such damaged rock and coal with various of CID will perform different mechanical characteristics, and will undergoes a complicated process of stress path evolution and/or energy release due to changing. The study on the mechanical properties of CID coal provides insight into the underground excavations and the design of supports for these openings under such time-dependent disturbances

Methods

Results

Discussion

Conclusion