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

Table 2

Calculation results of the brittleness index of granite under different loading modes.

Loading modes	Peak strain	Crack initiation strain	Strain difference	Bi	Bii	BI	Qualitative analysis of the test curve
	εc/%	εci/%	△ε=εc−εci	εci/△ε	S/S△	Bi·Bii
Unloading	0.003249	0.001828	0.001421	1.29	0.73	0.94	Brittleness
Compression	0.003746	0.001810	0.001936	0.93	0.43	0.40	Strain softening