Abstract
A series of numerical experiments have been conducted to investigate the intermediate principal stress effects on rock failure behaviors. The numerical results show that the strength and deformation of the rock samples are significantly affected by the intermediate principal stress. The effects are inconsistent in different intervals. As intermediate principal stress ratio b increases, the rock strength increases initially and finally decreases. When b is approximately equal to 0.5, the strength of the rock sample reaches the maximum. In the microlevel, the intermediate principal stress affects the number and distribution of microcracks. The increase of the intermediate principal stress makes the projection of the microcracks on the loading plane change from uniform to uneven. On the one hand, the intermediate principal stress restricts the propagation of microcracks in the normal direction along the intermediate principal stress (or with a component in this direction), which will lead to an increase in the strength of the rock samples. On the other hand, the propagation of microcracks along the normal direction with small principal stress (or with a component in this direction) is promoted, which leads to a decrease in the strength of the rock sample. End friction can make the intermediate principal stress effect more significant because the friction of the loading end to the rock sample can result in stress deviation between the actual value and experimental value. Inhomogeneity of stress field induced by the change of stress states or end friction forces is the external factor of the intermediate principal stress effect. Also, the inhomogeneity of rock material itself is the internal factor. Intermediate principal stress will promote or restrict the failure of certain directions, thus affecting the overall strength of the rock samples. The numerical results can be very meaningful for stability analysis of rock masses in practical engineering.
Highlights
Natural rock masses are generally in a three-dimensional stress state, which can be defined by three mutually perpendicular stress components (σ1, σ2, and σ3). It is an important subject in rock mechanics to study rock failure behaviors under three-dimensional stress conditions. e effect of the intermediate principal stress on rocks has been studied for many years, but it is still an unsolved problem
Three-dimensional unequal stress states are very common in engineering practice, and true triaxial rock strength measurements have shown that the intermediate principal stress does have an effect on rock strength
To provide a mechanism analysis from the microscopic level, a set of numerical experiments has been designed to conduct a detailed study on the intermediate principal stress effect on rock failure behaviors, including analysis of stresses, strains, failure model, acoustic emission (AE), crack developments, end frictions, and microuniformities
Summary
Natural rock masses are generally in a three-dimensional stress state, which can be defined by three mutually perpendicular stress components (σ1, σ2, and σ3) It is an important subject in rock mechanics to study rock failure behaviors under three-dimensional stress conditions. Tang and Hudson [10] have collected many simulation results using the RFPA code for studying the emergent properties of a heterogeneous microstructure In these numerical studies, the phenomenon of the intermediate principal stress effect has been reproduced. To provide a mechanism analysis from the microscopic level, a set of numerical experiments has been designed to conduct a detailed study on the intermediate principal stress effect on rock failure behaviors, including analysis of stresses, strains, failure model, acoustic emission (AE), crack developments, end frictions, and microuniformities. Based on the simulation results, the mechanism of intermediate principal stress effect has been discussed
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