Issue 49

C.Y. Liu et alii, Frattura ed Integrità Strutturale, 49 (2019) 557-567; DOI: 10.3221/IGF-ESIS.49.52 565 Figure 6: Changes of the marble brittleness indices under different surrounding rock pressures The brittleness index B L meets the feature that the brittleness decreases as the surrounding rock pressure increases. In addition, as the surrounding rock pressure increases, the decrease of the brittleness index B L is more linear than B 13 , which is more in line with the actual test results. For B 13 , the variation interval is not large, making it difficult to quantitatively measure the changes of brittleness. On the contrary, B L changes more significantly, which is also more in line with the actual test results. In summary, the brittleness index B L can give a more accurate quantitative description of rock brittleness and more accurately reflect its variations. In order to further explore the applicability of the brittleness index B L to different types of rocks under surrounding rock pressure and compare it with B 13 , this paper calculates the brittleness index B L according to the experimental data of different rocks under the surrounding rock pressure of 30MPa obtained by Chen Guoqing et al., as listed in Tab. 4, and draws the brittleness index variations of 5 types of rock samples under the tri-axial stress condition, as shown in Fig. 7. Rock sample type σ i /MPa /10 −3 σ p /Mpa ε p /10 −3 σ r /MPa ε r /10 −3 B 13 B L marble 75.917 1.515 134.521 11.24 126.537 24.337 0.554 0.010 sandstone 106.045 3.596 245.677 11.382 144.481 21.565 1.291 0.079 limestone 248.161 9.669 286.085 12.767 198.059 18.385 1.245 0.077 coarse grain granite 120.904 3.79 291.095 11.226 133.415 20.598 1.531 0.106 fine grain granite 145.194 1.93 476.75 8.8 9.716 22.212 1.534 0.184 Table 4: Mechanical parameters and calculated brittleness indices B 13 and B L of different rocks under surrounding rock pressure [18] Figure 7: Brittleness index variations of the 5 types of rocks under surrounding rock pressure