Abstract
The study of deformation, strength, and other mechanical characteristics of sandstone under true triaxial compression is significant for understanding failure mechanisms in rock and evaluating the stability of underground structures. Conventional and true triaxial compression tests for sandstone are conducted for different stress states in this study using the self‐developed true triaxial electrohydraulic servo test system combined with acoustic emission (AE) testing. This study presents an in‐depth and systematic investigation of deformation, strength, and AE characteristics. The results show significant differences in deformation, strength, and acoustic emission characteristics for the rock under conventional triaxial and true triaxial compression tests, respectively. The peak strength, axial strain, lateral strain, and incremental strain (in unstable crack growth stage) increase with increasing confining pressure under conventional triaxial compression, and the AE count gradually decreases while shear crack proportion gradually increases, indicating that increasing confining pressure gradually inhibits the shear slip effect along fractures, delays perforation of the rock shear fracture surface, and enhances the ability of the rock to withstand deformation and load. Under true triaxial compression, the peak strength increases and then decreases with increasing intermediate principal stress σ2 and the axial strain ε1 and lateral strain ε2 gradually decrease; besides, the lateral strain (expansion) of the rock is mainly in the minimum principal stress σ3 direction, and lateral expansion tends to decrease before increasing. AE events first weaken and then enhance with increasing σ2, and the proportion of shear cracks increases first and then decreases, indicating that the confining pressure gradually changes from the shear slip effect that controls crack offset to the damage effect that promotes crack tension with increasing σ2. In addition, the protective effect of confining pressure improves when σ3 increases.
Highlights
Rock material is a kind of brittle geological material, which has a complex composition and contains numerous defects, such as joints and cracks
The conventional triaxial and true triaxial tests of sandstone under di erent stress states are carried out using the self-developed true triaxial electrohydraulic servo test system
Deformation, strength, acoustic emission (AE) characteristic parameters, and development of the internal cracks are studied under di erent con ning pressures, intermediate principal stresses, and minimum principal stresses. e primary research results are summarized as follows: (1) e strength of the sandstone increases with increasing con ning pressure under conventional triaxial compression, while the strength of sandstone increases first and decreases with increasing intermediate principal stress under true triaxial compression. e strength under the true triaxial condition is consistent with the Mogi–Coulomb criterion. e rock is protected obviously, and the peak strength of the rock is greatly improved by increasing σ3
Summary
Rock material is a kind of brittle geological material, which has a complex composition and contains numerous defects, such as joints and cracks. Most true triaxial compression experiments examine strength and failure criteria for granite, marble, or other hard rocks, while failure and deformation characteristics for relatively soft rocks, such as sandstone and coal, remain largely unknown. Strength, and other mechanical properties of sandstone under true triaxial compression can provide reference for the selection of rock mechanics parameters in future geotechnical engineering projects. Erefore, it is necessary to explore the development of internal microcracks in rock based on AE to reveal the root cause of rock deformation and failure under true triaxial compression. E effects of different confining pressures under conventional triaxial compression and different stresses in true triaxial compression on the variation of rock deformation, strength parameters, and internal crack development are discussed Sandstone is subjected to conventional and true triaxial tests with varying stress conditions using the self-developed true triaxial electrohydraulic servo test system. e development of internal cracks within the rock is monitored using an AE monitoring system. e deformation, strength, and AE characteristics of sandstone under three triaxial stress states are discussed. e effects of different confining pressures under conventional triaxial compression and different stresses in true triaxial compression on the variation of rock deformation, strength parameters, and internal crack development are discussed
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