Water Infusion on the Stability of Coal Specimen under Different Static Stress Conditions

Zilong Zhou,Xin Cai,Lihai Tan

doi:10.3390/app10062043

Abstract

Underground coal mines are frequently subjected to water infusion, resulting in many mining hazards. This study investigated the effect of water infusion on the stress and energy evolution characteristics of coal specimens representing isolated pillars under different initial axial stress conditions using the discrete element method. A water infusion distribution model was developed, in which random functions were employed to describe water distribution for the purpose of realizing the dispersion of results for a better reliability. Based on the results, a stress-level classification was presented to evaluate the water effect on pillars’ instability. For the investigated coal specimens, the water weakening effect on stress and energy remains stable when the axial geo-stress on pillars is less than 65% of uniaxial compressive strength (UCS). In contrast, when the axial stress coefficient is greater than 65%, pillars become unstable eventually. A higher axial stress coefficient is more likely to introduce a lower critical instability point of the water saturation coefficient for pillars in the process of water infusion. However, the instability point remains random to some extent for specimens following the same water distribution rule under the identical test condition. Two instability types, which also happened randomly, were observed in the numerical results for damaged coal specimens under different water saturation coefficients and axial geo-stresses, namely free-falling and step-falling.

Highlights

In underground coal mines, the stability of coal pillars and the surrounding rock is a key factor controlling the stability of the cavity group system
They discovered that the peak stress and modulus during elastic, strain softening and post-peak regimes decrease as water content increases while the failure strain increases
Based on the equivalent strain hypothesis and statistical damage theory, they derived a constitutive model for the coal specimens with different water contents [19]

Summary

Introduction

The stability of coal pillars and the surrounding rock is a key factor controlling the stability of the cavity group system. It is worthwhile to study the mechanical behavior of coal rocks under watery conditions. White and Mazurkiewicz [17] conducted uniaxial compressive tests on Nemo coal specimens with different water contents. They found that with the increase of water content, the compressive strength and Young’s modulus of the Nemo coal specimen decrease. Yao et al [22] carried out similar tests on Xishahe coal specimens. They discovered that the peak stress and modulus during elastic, strain softening and post-peak regimes decrease as water content increases while the failure strain increases. Yao et al [20] obtained the damage evolution characteristics of coal specimens by means of acoustic emission technique

Objectives

Findings

Discussion

Conclusion