Issue 53

Y.D. Shou et alii, Frattura ed Integrità Strutturale, 53 (2020) 434-445; DOI: 10.3221/IGF-ESIS.53.34 436 have four confining stresses of 0MPa, 5 MPa, 10 MPa and 15 MPa. All tests were conducted under displacement-controlled conditions at average loading rate of 0.01 mm/min until the coal-rock sample is failure. Figure 1: The preparation of coal samples. (a) The pulverized coal collected from Songzao coal mining area in Chongqing; (b) The stress- controlled compressing machine for manufacture the coal samples; (c) The reconstituted coal sample. Figure 2: The rock mechanical triaxial test system. (a) The Servo-controlled Rock Mechanical Test System MTS815; (b) The installation of the coal samples. Experimental results According to the experimental data, the complete deviatoric stress-strain curves of the coal-rock under the different confining stress conditions can be obtained, as shown in Figs 3-6. It is found from Figs 3-6 that the overall trends of the complete deviatoric stress – strain curves are similar. The characteristics of the complete deviatoric stress – strain curves can be divided into three stages, which are the linear elastic stage, the elastic damage stage and the plastic damage stage. As shown in Fig. 3, the peak deviatoric stress 1 3   − of the coal-rock is 4.576 MPa and the corresponding axial strain 1  is 0.518% when the confining stress is 0 MPa. As shown in Fig. 4, the peak deviatoric stress 1 3   − of the coal-rock is 9.442 MPa and the corresponding axial strain 1  is 1.765 % and the corresponding transverse strain 3  is -0.956% when the confining stress is 5 MPa. As shown in Fig. 5, the peak deviatoric stress 1 3   − of the coal-rock is 12.832 MPa and the corresponding axial strain 1  is 3.146 % and the corresponding transverse strain 3  is -1.771% when the confining stress is 10 MPa. As shown in Fig. 6, the peak deviatoric stress 1 3   − of the coal-rock is 13.521 MPa and the corresponding