Creep characteristics and nonlinear constitutive modeling of coal rock containing pressure relief boreholes

Tian Guanghui; Zhang Liyi; Zhang Qingzhao; Liu Weijian; Zhang Zhizeng

doi:10.16186/j.cnki.1673-9787.2024010047

Abstract：Objectives The influence of pressure relief borehole diameter on the long-term stability of pres-sure relief roadways is investigated through graded loading creep tests on coal rock specimens with different borehole diameters.Methods First,creep characteristics and long-term stability of coal rock are compara-tively analyzed for different pressure relief borehole diameters.Second,Najar damage theory is introduced to analyze damage characteristics of coal rock during creep stages from an energy perspective.Third,con-sidering the hardening effect of viscosity coefficient as a time-dependent non-stationary parameter,a param-eter nonlinear constitutive equation is proposed.Finally,the steady-state creep rate inflection point method is employed to determine the long-term strength of coal rock with different borehole diameters.Results The results indicate that the pressure relief borehole diameter significantly influences creep characteristics,creep damage and long-term strength of coal rock.During creep,the pressure relief borehole diameter ex-hibits a distinct size effect on both creep strain and initial creep rate,with larger boreholes resulting in greater creep strain and higher initial creep rate.Throughout the creep process,damage gradually increases while damage rate decreases and eventually stabilizes,with damage showing a positive correlation with borehole diameter.The derived parameter-nonlinear Maxwell creep equation,incorporating with the viscos-ity coefficient,accurately describes the creep process.Long-term strength demonstrates a negative correla-tion with borehole diameter.Conclusions The findings contribute to maintaining long-term stability of pres-sure relief roadways and provide theoretical insights for rockburst prediction and mine safety.