Abstract
3-D particle-based discrete element method (PB-DEM) was employed to numerically study the mechanical and progressive failure characteristics of pre-fissured marble specimens under conventional triaxial unloading conditions. The microscopic parameters of PB-DEM for marble materials were calibrated using comparison with the previous experimental data. To systematically investigate the mechanical properties and the progressive failure characteristics of pre-fissured marble specimens under the unloading conditions, a series of numerical specimens were simulated. The effects of fissure geometric conditions, initial confining pressures, and unloading rates on the mechanical and failure behaviors were explored via simulations. The present numerical results indicate that peak strength increased as the initial confining pressures increased or the unloading rate decreased. Crack coalescence types and the ultimate failure modes in the pre-fissured marble specimens were significantly affected by the unloading stress paths. The present numerical results provide a better understanding of unloading mechanical and failure characteristics to scientists and engineers in rock mechanics and rock engineering.
Highlights
In nature, geologic tectonic activities result in the formation of different scale of discontinuous structures, such as pores, fissures, joints, and faults, in rock masses, which have significant influence on the mechanical properties, stability, and safety of rock masses in geotechnical engineering, such as mineral engineering, foundation pit engineering, tunnel engineering, and deep energy engineering [1,2,3].On the other hand, rock masses with discontinuities are located in a three-dimensional state in situ before being excavation
Setup pre-fissured marble specimens of Type-A ~ Type-D, crack lengths were fixed as 24 mm, and ligament lengths were fixed as 33 mm, which resulted in various ligament inclination angles in these marble specimens, as shown in Figure 6 and Table 2
When the initial fissure inclination angle α and initial fissure length a were fixed, it can be found from Figure 8a,e,f that the mixed tensile–shear crack coalescence appeared in the rock bridge region, which resulted in the ultimate mixed tensile–shear failure of pre-fissured marble specimens
Summary
Geologic tectonic activities result in the formation of different scale of discontinuous structures, such as pores, fissures, joints, and faults, in rock masses, which have significant influence on the mechanical properties, stability, and safety of rock masses in geotechnical engineering, such as mineral engineering, foundation pit engineering, tunnel engineering, and deep energy engineering [1,2,3]. Some scholars investigated crack propagation and coalescence behaviors and mechanism of rock specimens with two or multiple pre-existing fissures under uniaxial and conventional triaxial compressive loading conditions [5,6,7,8,9,10,11,12,13,14,15,16,17,18]. Wang et al [30] developed stress-based failure criteria in the non-ordinary state-based peridynamics to investigate the crack initiation, propagation, and coalescence in the pre-fissured rock specimens under uniaxial and biaxial compressive loading. Zhou et al [36,37] implemented the phase field model into COMSOL to study the fracture behavior of rock specimens with pre-existing fissures subjected to the uniaxial compressive loads.
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