Abstract
Failure behavior of pillars in deep mines is affected by various cyclic loads that cause initial pre-damage. Pillars will be further damaged and developed in the long-term compressive stress until they are destroyed. To reveal the strength characteristics and crack damage fracture laws after rock pre-damage, uniaxial compression tests were carried out on granite specimens damaged by cyclic loading using the digital speckle correlation method. The experimental results indicate that the mechanical properties of pre-damaged specimens show large damage differences for different cycles. The damage variable of the pre-damaged specimens increases with the increase of cycle number and confining pressure. The damage of specimens is primarily due to the strength weakening effect caused by cycle numbers, and the confining pressure restriction effect is not obvious. The evolution laws of uniaxial compression damage propagation in the pre-damaged specimens show differences and obvious localization phenomenon. Pre-damaged specimens experienced three failure modes in the uniaxial compression test, namely tensile shear failure (Mode I), quasi-coplanar shear failure (Mode II), and stepped path failure (Mode III), and under different pre-damage stress environments with high confining pressures, the failure modes are dominated by Mode II and Mode III, respectively.
Highlights
Published: 28 September 2021Instability in rock engineering is primarily due to the further expansion of joints, faults, and cracks [1]
Chen et al [9] analyzed the crack propagation laws of the granite in three fatigue stages during uniaxial cyclic loading, and the results showed that distinguishing crack growth was identified in quartz grains at the initial degradation stage
Wang et al [14] studied the effects of volumetric change on the granite fatigue performances under triaxial cyclic loading, and they found that the stress level corresponding to the transition from volumetric compaction to volumetric dilation could be considered as the threshold for fatigue failure
Summary
Instability in rock engineering is primarily due to the further expansion of joints, faults, and cracks [1]. Wang et al [14] studied the effects of volumetric change on the granite fatigue performances under triaxial cyclic loading (confining pressure was 3–10 MPa), and they found that the stress level corresponding to the transition from volumetric compaction to volumetric dilation could be considered as the threshold for fatigue failure. Liu et al [15] studied the effects of the confining pressure (2–50 MPa) and frequencies on the sandstone damage evolution during cyclic loading and unloading. Sun et al [19] combined uniaxial compression tests with DSCM to research deformation field evolution laws of backfill specimens. Uniaxial stress-resistance tests were conducted on granite specimens with various cyclic loading numbers, and the strength characteristics, damage evolution, specimens were first subjected to a triaxial compression test. (c) uniaxial compression rigidity testing machine; (d) DSCM acquisition system
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