Issue 49

C.Y. Liu et alii, Frattura ed Integrità Strutturale, 49 (2019) 557-567; DOI: 10.3221/IGF-ESIS.49.52 558 effects of disasters on underground engineering and improve mining efficiency, it is extremely important for scientific research to figure out how to accurately evaluate the brittleness of rocks. 1 = ⁄ , 2 = ( − ) ( + ) ⁄ , 3 = 2⁄ , 4 = √ 3 and are the UCS and the tensile strength, respectively. 5 = 5 ′ 5 " , 5 ′ = ( − )/( − ) , 5 " = + + , CS = ( − )/ / ( − ) ε , ε , ε are the peak strain, the peak strain maximum and the minimum value of sample rock specimen, respectively. , , are the standardized coefficients. and are the peak strength and the residual strength, respectively. and are the peak strain and the residual strain, respectively. 6 = ( − )/ , 7 = / M and E are the post-peak modulus and the pro-peak elastic modulus, respectively. 8 = ( − )/ , 9 = ( − )/ , 10 = / and are the peak strength and the residual strength, respectively. and are the peak strain and the residual strain, respectively, is the reversible strain of the stress-strain curve. 11 = 11 ′ 11 " , 11 ′ = ( − )/ , 11 " = lg| | /10 and are the peak strength and the residual strength, respectively. is the post-peak stress drop rate. 12 = 12 ′ + 12 " , 12 ′ = ( − )/( − ) , 12 " = ( − )( − )/( ) and are the peak strength and the residual strength, respectively, and are the peak strain and the residual strain, respectively. 13 = 13 ′ + 13 ′′ , 13 ′ = ( p − i ) ( − ⁄ i ) ， 13 ′′ = ( p − r )⁄ ( − ) and are the peak strength and the residual strength, respectively. and are the peak strain and the residual strain, respectively, i and i are the crack initiation stress and the crack initiation strain 14 = , 15 = 45° + /2 is the inner friction angle determined from Mohr’s envelope. 16 = 0.5 + 0.5 , = ( − 1)/(8 − 1) × 100 , = (0.4 − 1)/ (0.4 − 0.15) E and are the post-peak modulus and the elastic modulus, respectively. 17 = ( − )/ where H μ is the micro-indentation hardness, H m is the macro-indentation hardness, and c is the constant 18 = / where H a is hardness and K c is fracture toughness. 19 = / 2 where H a and K c are same as those in B 18 , E is Young’s modulus 19 = /( + + ), W qtz , W carb and W clay are the content of quartz, clay and carbonate minerals, respectively. Table 1 : Formula meaning and explanation.