Abstract
Loading and unloading stress paths play critical roles in investigating the deformation and failure of roadway excavation. In this study, tests under four different loading and unloading stress paths were conducted on red sandstone samples, with the aid of a self-developed true triaxial test system. Meanwhile, the deformation and failure characteristics of the samples were monitored during the tests. The following research conclusions were obtained: The octahedral shear stress is linearly correlated with the average effective stress, and the correlation coefficient R2 is 0.9825. The Mogi–Coulomb strength criterion is superior to the Drucker–Prager strength criterion in reflecting strength failure characteristics of red sandstone during loading and unloading. Shear failure tends to occur under uniaxial compression, whereas shear–tensile composite failure occurs under loading and unloading conditions. Compared with the true triaxial loading test, loading and unloading tests produce a larger strain in the unloading direction. Under loading and unloading stress paths, with the increase in intermediate principal stress (IPS), the strain in the direction of IPS gradually changes from expansion to compression, and the peak strength gradually increases. The state of IPS affects the failure strength of the sample and reflects the strengthening effect of IPS. This paper boasts a certain value and significance for research on the deformation and failure characteristics of sandstone in the actual in situ stress environment with triaxial dynamic changes.
Highlights
Published: 5 February 2022The underground rock mass is in the original rock stress state before mining
It is verified that the Mogi–Coulomb criterion is suitable for true triaxial loading tests and has a good linear relationship for rock strength under true triaxial continuous loading and unloading conditions
A total of four tests under different true triaxial loading and unloading stress paths, i.e., loading–constant–constant test (LCCT), loading–constant–unloading test (LCUT), loading–unloading–unloading test (LUUT), and loading–loading–unloading test (LLUT), were conducted with the initial triaxial principal stresses σ1, σ2 and σ3 in the true triaxial test set to 20 MPa, 20 MPa, and 10 MPa, respectively
Summary
The underground rock mass is in the original rock stress state before mining. Due to the existence of tectonic stress, the stress of rock mass in a stratum is generally in the true triaxial state (σ1 > σ2 6= σ3 ) [1,2]. Research on the law of rock mechanical properties under true triaxial loading and unloading stress paths can faithfully reflect changes of the triaxial stress state of rock, thereby revealing the failure mechanism of underground rock excavation. Haimson and Chang [21,22] developed a new true triaxial test system and obtained that an increase in the intermediate principal stress (IPS) could enhance the strength of rock. The strength variation characteristics and failure criteria of rock under complex stress paths with continuous and dynamic IPS change still need to be further explored. Based on the test results, the influence of continuous IPS changes on the deformation characteristics of red sandstone was discussed, and the failure criteria of red sandstone under four stress paths were explored. It is verified that the Mogi–Coulomb criterion is suitable for true triaxial loading tests and has a good linear relationship for rock strength under true triaxial continuous loading and unloading conditions
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