Experimental Investigations on Creep Behavior of Coal under Combined Compression and Shear Loading

Rongbin Hou,Yanke Shi,Duoxin Zhang,Luyang Shi,Leige Xu,Yi Xue

doi:10.1155/2021/9965228

Abstract

The creep behavior of rock has received much attention for analyzing the long-term response and stability of underground rock engineering structures. Numerous studies have been carried out on the creep properties of various rocks under pure compression conditions. However, little attention has been paid to the creep behavior of rocks in a combined compression-shear loading state. In this work, a novel combined compression and shear test (C-CAST) system was used to carry out inclined uniaxial compression tests and creep tests for various inclination angles (0°, 5°, 10°, and 15°). The results revealed that the peak strength of the coal decreased with the inclination angle of the specimen, which could provide the basis for setting up a creep test scheme. Multistage compression-shear creep tests were carried out on specimens with different inclination angles. Based on the analysis of the creep test data, the creep behavior of the coal in a combined compression-shear state was studied. It was found that the specimen inclination affected the time-dependent deformation, long-term strength (LTS), and time to failure. Compared with the specimen under pure compression, the inclination specimens tend to produce large shear strain with time, while they were more prone to shear failure. The reduction of the long-term strength was closely associated with the increase of the specimen inclination angle when the angle was more than 5°. Moreover, the ratio of the peak strength to the LTS was not affected by the specimen inclination, which is considered an inherent characteristic. We anticipate that the results obtained will assist in pillar design and long-term stability analysis.

Highlights

Pillars are common rock structures in underground coal mining that are used to control ground subsidence [1, 2], protect a roadway [3,4,5], and isolate the underground water in a goaf [6,7,8]
Pariseau [14] and Foroughi and Vutukuri [15] have noted in their studies that the estimation of the pillar stability in an inclination coal seam becomes complicated based on whether or not the rock structures are in a compression-shear loading condition
The peak strength and strain decreased with the increase of the inclination angle, but this law was not obvious when the inclination angle was in the range of 0°–5°

Summary

Introduction

Pillars are common rock structures in underground coal mining that are used to control ground subsidence [1, 2], protect a roadway [3,4,5], and isolate the underground water in a goaf [6,7,8]. The axes of the pillars are usually not parallel to the direction of maximum in situ principal stress in mining practices, such as the loading condition of coal pillars in an inclination coal seam In this case, if the UCS of the rock is substituted into the strength formula of the inclination pillars, the strength of the coal pillar will be overestimated [12, 13]. Pariseau [14] and Foroughi and Vutukuri [15] have noted in their studies that the estimation of the pillar stability in an inclination coal seam becomes complicated based on whether or not the rock structures are in a compression-shear loading condition. A detailed understanding of the creep behavior of coal in a combined compression-shear

Methods

Results

Conclusion