Energy Evolution and Acoustic Emission Characteristics of Sandstone Specimens under Unloading Confining Pressure

Table 2

Strain energy at peak strength points or the rock specimen under unloading confining pressure.

Initial value σ3 (MPa)	Peak value σ3 (MPa)	σ1–σ3 (MPa)	U1 (kJ·m^−3)	U3 (kJ·m^−3)	U^e (kJ·m^−3)	U^d (kJ·m^−3)
5	3.32	96.82	375.50	−46.80	262.82	69.13
10	4.53	117.22	590.30	−118.46	363.89	123.48
15	6.86	141.33	848.59	−183.33	517.71	171.20
20	10.58	156.21	1003.50	−225.64	636.65	176.46