Abstract
The TRW‐3000 true triaxial rock testing machine was used to conduct loading and unloading tests of sandstone under different σ2, and the true triaxial lateral unloading mechanics and energy characteristics of sandstone under different σ2 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 σ3 path is reduced, the unloading direction has obvious expansion and deformation, and the amount of expansion increases significantly with the increase of σ2; 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 σ3 path are reduced. (3) Under the condition of unloading σ3, U, Ue, and Ud, when the specimen is broken, are all linearly positively correlated with σ2. Ud increases nonlinearly with the increase of H, and as σ2 increases, the slope of the Ud -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 σ3 path is converted into Ue, but as σ2 increases, Ud /U increases, and the energy consumed when the specimen is broken is greater.
Highlights
In recent years, a substantial number of laboratory tests were conducted to reveal the macromechanical and failure behaviors of rock masses under different loads, e g., uniaxial compression, conventional triaxial compression [8], and true triaxial compression [9, 10]
In order to investigate the influence of initiation and propagation of microcracks on the failure of rock materials, micromechanical methods [18,19,20] were employed to understand the failure of rock materials and establish the corresponding strength criteria and constitutive relations
Zhou et al [21] proposed a nonlinear three-dimensional strength criterion for rock-like materials based on the micromechanical methods, in which the effects of the intermediate principal stress on the failure of rock-like materials are taken into account
Summary
To explore the influence of σ2 on the true triaxial unloading mechanics and energy characteristics of sandstone, a true triaxial loading and unloading test was carried out. 30 s, when σ2 and σ3 remained unchanged, σ1 was loaded until specimens were destroyed. Part II: true triaxial lateral unloading: 30 s, when σ2 and σ3 remained unchanged, σ1 was loaded to a predetermined value (90% of the peak strength σ max 1 obtained by the true triaxial loading test under the same initial stress condition). Step 3: σ1 and σ2 were kept stable, and σ3 was unloaded until specimens were destroyed.
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