An Evaluation Method of Rock Brittleness Based on the Prepeak Crack Initiation and Postpeak Stress Drop Characteristics

Table 4

Classification and description of brittleness index B1.

Grade	B1	Description
1	1	M⟶−∞, ideal brittleness
2	0.6321∼1	−∞ < M < − E, high brittleness
3	0.6321	M = − E
4	0∼0.6321	−E < M < 0, low brittleness
5	0	M = 0, ideal plasticity
6	<0	M > 0, strain hardening