The TRW-3000 true triaxial rock testing machine was used to conduct loading and unloading tests of sandstone under different
σ
2
, and the true triaxial lateral unloading mechanics and energy characteristics of sandstone under different
σ
2
were studied. The experimental results show the following: (1) compared with the results of the loading test, the peak strength of the sandstone under the unloading
σ
3
path is reduced, the unloading direction has obvious expansion and deformation, and the amount of expansion increases significantly with the increase of
σ
2
; sudden brittle failure occurs at the end of unloading. E gradually decreases with the increase of H, and it performs well to use the cubic polynomial to fit the curve of E-H. (2) The Mogi–Coulomb strength criterion can accurately describe the true triaxial strength characteristics of sandstone under loading and unloading conditions. Compared with the results of the loading test, the values of c and φ obtained based on this criterion under the unloading
σ
3
path are reduced. (3) Under the condition of unloading
σ
3
, U,
U
e
, and
U
d
, when the specimen is broken, are all linearly positively correlated with
σ
2
.
U
d
increases nonlinearly with the increase of H, and as
σ
2
increases, the slope of the
U
d
-H curve becomes larger, and the specimen consumes more energy under the same unloading amount. Most of the energy absorbed by the specimen under the unloading
σ
3
path is converted into
U
e
, but as
σ
2
increases,
U
d
/
U
increases, and the energy consumed when the specimen is broken is greater.
Unloading Mechanics and Energy Characteristics of Sandstone under Different Intermediate Principal Stress Conditions
