Experimental investigation of the creep damage evolution of coal rock around gas extraction boreholes at different water contents

Abstract

The creep process of the coal rock around the extraction boreholes under stress-water coupling is an important factor affecting the stability of the boreholes. To study the influence of the water content of perimeter of the coal rock around the boreholes on its creep damage, a creep intrinsic model considering water damage was established by introducing the plastic element model from the Nishihara model. To study the steady-state strain and damage evolution of coal rocks containing pores, and verify the practicality of the model, a graded loading water-bearing creep test was designed to explore the role of different water-bearing conditions in the creep process. The following conclusions were obtained: 1) water has a physical erosion and softening water wedge effect on the perimeter of the coal rock around the boreholes, which affects the loading axial strain and displacement of the perforated specimens; 2) an increase in water content reduces the time taken for perforated specimens to enter the creep phase, making the accelerated creep phase come earlier; 3) the parameters of the water damage model are considered to be exponentially related with the water content. The experimental data are similar to the results of the model parameters, and the model shows some practicality; 4) the damage variables in the accelerated creep phase increase rapidly throughout the creep process, leading to local instability in the borehole. The findings of the study provide important theoretical implications for the study of instability in gas extraction boreholes.

Thickness and Strength Analysis of Prestressed Anchor (Cable) Compression Arch Based on Safe Co-Mining of Deep Coal and Gas

“…The relationship between the thickness of the compression arch of the bolt (cable) and the length and spacing of the bolt (cable) is shown in (5).…”

“…Deep coal seams have a large amount of gas [1]. Through the excavation of gas extraction roadways [2], arranging coal seam drilling and gas extraction devices in the roadway for gas extraction is widely used in engineering [3][4][5]. However, due to the complex and changeable deep geological conditions and significant ground stress, it is difficult for conventional support to maintain the stability of the roadway [6][7][8][9][10].…”

A Fractional-Order Creep Model of Water-Immersed Coal

“…The softening effect of water on coal is mainly due to the dissolution of water on the microstructure of coal [39]. Many scholars have pointed out that coal undergoes corrosion effects and crack propagation during immersion [22,40,41]. This paper conducted structural observation in the coal immersed for 14 days with a microscope magnification of 100×.…”

Ultrasonic characteristics and equivalent crack width of coal and rock bodies around boreholes during progressive failure

“…The reason is not only the poor permeability of coal seam [ 5 ], but also that under the influence of some factors such as permeability enhancement, tunneling and mining. The special structure of the borehole leads to the failure of coal around the borehole [ 6 ], resulting in a large number of crack networks, forming air leakage channels and seriously reducing the concentration of gas extraction [ 7 ]. To improve the effect of gas extraction, it is necessary to analyze the crack propagation mechanism of the coal and rock bodies around boreholes and explore the development of the crack channel around boreholes using specific technical measures [ 8 , 9 ].…”