Failure modes affected by stress concentration in gneiss: laboratory triaxial experiment and numerical reproduction

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Abstract
Since infrastructure development has increasingly encountered gneiss, and its complex mechanical characteristics have brought engineering much hardship, research on gneiss has been booming. However, the stress concentration effect in gneiss has seldom been studied. This work found an under-discussed phenomenon and tried to explain it by the stress concentration effect. Specifically, triaxial compression experiments with different confined pressures on gneiss samples with different embedded textures and an improved Cosserat constitutive model were employed to study the textures in gneiss. The constitutive model was meant to simulate the experiment by adjusting the stress concentration effect in the texture areas in gneiss samples. The phenomenon found in the experiment for discussion was that the different textures in gneiss can cause different failure modes but not necessarily affect its compression strength. The phenomenon was then successfully reproduced by the finite element method with the improved Cosserat model by setting different stress concentration degrees in the textures. The experimental and simulation results revealed a potential mechanism to explain the phenomenon: the diverse failure modes observed in gneiss samples with identical strength may result from variations in stress concentration distributions. Lastly, a new method to trigger strain localization by setting stress concentration regions is proposed based on the analysis. This work may provide a different understanding of the failures in rocks with directional textures and inspire studies in localized stress concentration effects.

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