Creep and damage characteristics of coal rock under different stresses

Creep curves of coal rock specimens 3# and 5#from Hancheng area were obtained by triaxial creep test under 9 MPa confining pressure through multi-stage loading. Creep constitutive equations under different stress level were established on the basis of the rheological theory of rock and data of creep tests, and the parameters in constitutive equations were identified through test data. The results show that the creep curves of coal rock specimens 3# and 5#are composed of instantaneous deformation stage, decay creep stage and stable creep stage. While differential stresses are less than 60% and 40% of the corresponding instantaneous compressive strength, respectively. The strain rate is nearly zero in the stable creep stage. While differential stresses are 60%-80% and 40%-80% of the corresponding instantaneous compressive strength, respectively, the strain rate is a constant in the stable creep stage. The creep curves of 3#and 5#coal rock specimen show the characteristics of brittle failure and toughness-brittle failure respectively while the differential stresses are above 80% of its instantaneous compressive strength.