Issue 49

C.Y. Liu et alii, Frattura ed Integrità Strutturale, 49 (2019) 557-567; DOI: 10.3221/IGF-ESIS.49.52 564 them. In addition, the fracture angles of the cores are also gradually reduced. In summary, as the surrounding rock pressure increases, the core brittleness gradually decreases, but through the analysis of Fig. 5, it is found that only the brittleness index B L satisfies this feature under a surrounding rock pressure range of 15MPa-25MPa. Therefore, the brittleness index B L is an effective supplement to B 8 , B 11 and B 12 . 0MPa 12MPa (a) (b) Figure 4: Mechanical Test Results of Two Groups of Cores 15MPa 18MPa 25MPa (c) (d) (e) Figure 5: Mechanical Test Results of Three Groups of Cores In addition, since it is difficult to obtain the accurate crack initiation stress and crack initiation strain during the test, the following section will use the experimental results of Chen Guoqing et al. to further compare and verify the brittleness indices B L and B 13 . F URTHER VERIFICATION OF THE ACCURACY AND APPLICABILITY OF THE BRITTLENESS INDEX B L UNDER SURROUNDING ROCK PRESSURE his section will further verify the accuracy and applicability of the brittleness index B L based on the existing experimental data. Tab. 3 shows the brittleness index B L calculated according to the experimental data of marble cores under different surrounding rock pressures obtained by Chen Guoqing et al.. At the same time, this paper draws the plots of the brittleness indices B L and B 13 changing with the surrounding rock pressure in order to facilitate the comparison with the brittleness index B 13 , as shown in Fig. 6. Confining pressure/ MPa σ i /MPa /10 −3 σ p /MPa ε p /10 −3 σ r /MPa ε r /10 −3 B 13 B L 5 87.929 1.693 192.084 3.729 71.956 5.976 2.031 0.446 15 89.354 1.589 258.749 4.867 123.939 7.434 1.960 0.310 25 116.041 1.967 297.072 5.615 162.811 8.174 1.930 0.257 35 126.055 1.943 332.891 6.393 190.99 10.716 1.523 0.165 Table 3: Mechanical parameters of cores and calculation results of brittleness indices B 13 and B L under surrounding rock pressure T