A New Bursting Liability Evaluation Index for Coal –The Effective Elastic Strain Energy Release Rate

Zhiguo Lu,Wenjun Ju,Kang Yi,Youliang Feng,Fuqiang Gao,Zhuoyue Sun,Hao Wang

doi:10.3390/en12193734

Abstract

Because both faults and cleats exist in coal, sharp stress drops occur during loading when coal is deformed. These drops occur during the pre-peak stage and are accompanied by sudden energy releases. After a stress drop, the stress climbs slowly following a zigzag path and the energy accumulated during the pre-peak stage is unstable. A stress–strain curve is the basic tool used to evaluate the bursting liability of coal. Based on energy accumulation in an unsteady state, the pre-peak stress–strain curve is divided into three stages: pre-extreme, stress drop, and re-rising stage. The energy evolution of the specimen during each stage is analyzed. In this paper, an index called the effective elastic strain energy release rate (EESERR) index is proposed and used to evaluate the coal’s bursting liability. The paper shows that the propagation and coalescence of cracks is accompanied by energy release. The stress climb following a zigzag path prolongs the plastic deformation stage. This causes a significant difference between the work done by a hydraulic press during a laboratory uniaxial compression experiment and the elastic strain energy stored in the specimen during the experiment, so the evaluation result of the burst energy index would be too high. The determination of bursting liability is a comprehensive evaluation of the elastic strain energy accumulated in coal that is released when the specimen is damaged. The index proposed in this paper fully integrates the energy evolution of coal samples being damaged by loading, the amount of elastic strain energy released during the sample failure divided by the failure time is the energy release rate. The calculation method is simplified so that the uniaxial compressive strength and elastic modulus are included which makes the new index more universal and comprehensive. Theoretical analysis and physical compression experiments validate the reliability of the evaluation.

Highlights

Safety and efficiency are two of the major goals in mining [1]
The bursting liability index is a value that represents the release rate of a coal sample’s accumulated elastic strain energy when it is fractured under a load [36]
It is the amount of elastic strain energy released per unit time when the coal sample is destroyed or the rate at which the elastic strain energy is transformed into kinetic energy

Summary

Introduction

Safety and efficiency are two of the major goals in mining [1]. As coal mine production and mining depths in China increase, coal burst accidents are occurring more frequently. The number of coal mines susceptible to coal bursts in China has increased from 32 in 1985 to 177 in 2016. The dust produced by coal burst accidents seriously affects the working environment [2]. This seriously threatens efficient production and the safety of workers and mine infrastructure [1,2,3,4,5]. A considerable number of research projects on coal bursts have made significant progress on predicting the occurrence of coal bursts and numerous theories and prediction indexes have been proposed

Methods

Results

Conclusion