Abstract
Crack initiation is an important stage in the failure process of rock masses. In this paper, crack initiation behaviors (crack initiation model, crack initiation location, crack initiation angle, and crack initiation stress) of granite specimens containing crossing-double-flaws with different lengths were investigated using PFC2D software. Crack initiation models were all tensile wing cracks, which did not exactly initiate from the main flaw with a length of 30 mm. They can initiate from the secondary flaw with a length 20 mm at α of 30° (included angle between main flaw and horizontal direction) and β of 90° (included angle between main and secondary flaws) and from main and secondary flaws at α of 30° and β of 60°. These were mainly induced by the superposition of stress fields around the main and secondary flaws as β varied from 0° to 90°, especially the tensile force concentration zones superposition. The tensile forces concentration zone around flaw shrank towards flaw tips with the increase of flaw’s inclinations measured horizontally. Under stress field superposition effects, the crack initiation stress decreased firstly and then increased with β at α of 30° and 45°. Crack initiation locations were close to flaw tips but not restricted to them. The distances between crack initiation locations and flaw tips, and the crack initiation angles depended on the flaw where first macrocracks initiated from. Microdisplacement field distributions of granite specimens to reveal the mesomechanism of crack initiation behaviors were discussed.
Highlights
The uniaxial compression tests on the granite specimens containing crossing-double-flaws with different lengths were simulated by Particle Flow Code (PFC). eir crack initiation behaviors were the main target of this investigation, including the crack initiation model, crack initiation location, crack initiation angle, and crack initiation stress
The secondary flaws tips became more and more close to the tensile force concentration zone close to main flaw tips. erefore, the tensile force concentrations close to secondary flaw tips were enhanced with β, which were crowded by less black segments and more red segments, especially at α of 30° and β of 90°
The uniaxial compression tests on granite specimens with crossing-double-flaws of different lengths were simulated by PFC. e crack initiation behaviors of granite specimens were studied. e following conclusions were achieved: (1) Crack initiation models were all tensile wing cracks
Summary
The rock masses contain various discontinuities such as joints, fissures, cracks, and faults [1,2,3,4,5,6,7,8]. e failure process of rock masses is characterized by several distinct deformation stages, including the crack initiation, propagation, and coalescence. The investigations on crack initiation behaviors have been conducted on the rock or rock-like specimens with artificial flaws by the laboratory tests and numerical simulations Most of these studies have been performed on different materials containing single flaw [11,12,13,14], two or more parallel flaws [15,16,17,18,19], two or more nonparallel flaws [20,21,22,23], three flaws [24,25,26], and threedimensional (3D) flaws [27,28,29]. Ere are few studies on the crack initiation behavior of rock specimen containing crossingflaws In this investigation, the uniaxial compression tests on the granite specimens containing crossing-double-flaws with different lengths were simulated by Particle Flow Code (PFC). The uniaxial compression tests on the granite specimens containing crossing-double-flaws with different lengths were simulated by Particle Flow Code (PFC). eir crack initiation behaviors were the main target of this investigation, including the crack initiation model, crack initiation location, crack initiation angle, and crack initiation stress
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