Energy release induced rockbursts based on butterfly-shaped plastic zones in roadways of coal reservoirs.

Xu Gao,Haoyu Shi,Jicheng Feng,Zhenkai Ma,Jianguo Wang

doi:10.1371/journal.pone.0255044

Abstract

According to the theories of rockburst based on butterfly-shaped plastic zones, a plane strain mechanical model was established for stress distribution around the holes in homogeneous elastoplastic media. Based on the Mohr-Coulomb yield criterion and the generalized form of Hooke's law, the equation for the elastic strain-energy density of units at a 3D stress state was deduced. On this basis, the energy absorption and release in rocks surrounding a roadway during the evolution thereof in a coal reservoir tend to rock bursting were quantified. Through Flac3D 5.0 numerical simulation software, the energy released from a homogeneous circular roadway at different development states of plastic zones was investigated. By investigating conditions at the 21141 working face in Qianqiu Coal Mine, Henan Province, China, subjected to rockburst, a numerical model was established to calculate the energy released by a rockburst working face. The calculated results approximated the data monitored at the outburst site, with the same energy level recorded. The theoretical calculation for energy release from the rock surrounding a roadway is expected to reference engineering practice.

Highlights

With increasing mining depths and coal resource extraction, various dynamic disasters, such as rockburst in mines, are becoming increasingly severe
The mechanism of occurrence of rockburst based on butterfly-shaped plastic zones in homogeneous circular roadways suggests that, in homogeneous circular roadways and surrounding rock media, butterfly-shaped plastic zones occur in the rock surrounding the roadways after the ratio of principal regional stress rises to a particular level
When the ratio of confining pressure rise to about 2.6, the plastic zones of surrounding rocks in the roadway start to expand in a butterfly shape, and the strain energy release increases exponentially

Summary

Introduction

With increasing mining depths and coal resource extraction, various dynamic disasters, such as rockburst in mines, are becoming increasingly severe. Literature [11] proposed that a rockburst in a coal mine was a non-linear dynamic process (from steady energy accumulation to unsteady energy release) of coal and rock mass system during its deformation. Literature [17] suggested that under particular stress and surrounding rock environment, roadways’ local stress field was suddenly changed due to triggering events These generated a butterfly-shaped plastic zone in surrounding rock to expand ergodically and release elastic energy stored in the body of the coal mass and surrounding rock system in the form of tremors, sound, and bursting of coal and rock masses. The above works suggest that rockburst results from energy dissipation and release, which is a non-linear dynamic process during rock mass deformation. The results can reference the stability and control of deep engineering activities, such as mines, tunnels, and water conservancy

A brief introduction to butterfly plastic zone

Sources of energies for rockburst occurring in roadways in coal reservoirs

Theoretical expression for elastic energy release from homogeneous media

Rockburst accidents

Establishment of a numerical model

Conclusion