基于三角孔应力集中效应的岩桥破断机制研究

Research on fracture mechanism of rock bridge based on stress concentration effect of triangular hole

确定三角孔与软岩裂隙间的合理距离及夹角,对提高静力膨胀法破裂软岩的效率有重要意义。通过对三角孔带单裂隙的类软岩试样进行静力膨胀试验及数值模拟,详细分析了预制裂隙与三角孔之间不同间距、不同走向条件下贯通岩桥后的试样断裂程度。结果表明:试样只沿三角孔的角平分线方向发育3条主裂纹;45°~90°范围走向的预制裂隙试样破裂后的裂纹数量比0°~30°范围的裂纹数量增加了30.4%~44.2%;0°走向试样的分形维数和断裂密度远低于45°和90°走向试样的分形维数和断裂密度;45°~90°走向的预制裂隙有利于试样的破裂,裂隙与孔之间的距离对破碎试样的效果影响较小;在0°~30°走向范围内,预制裂隙起着屏蔽作用,阻碍着试样的断裂,在2倍等效半径内,屏蔽作用明显,大于2倍等效半径时屏蔽作用基本消失。

This paper aims to determine the reasonable spacing and angle between the triangular hole and the soft rock fissure according to the stress concentration effect of the triangular hole,so as to accelerate the formation of the rock mass fissure network and improve the efficiency of the rock breaking.The static expansion test was carried out on the soft rock-like sample with triangular holes,and the static strain gauge and digital image system were used to monitor the expansion test process in realtime.Then,the PFC software was used to perform extended studies.Finally,based on the strain curve,fractal dimension,fracture density,and the number of cracks,the fracture degree of the specimens after penetrating the rock bridge under different conditions(e.g.,different strikes,and different spacings between prefabricated cracks and triangular holes)was quantitatively analyzed.The results show that prefabricated cracks can change the direction of crack development,while this effect is not as good as the directional crack formation effect of triangular holes.The sample only had three main cracks along the angle bisector of the triangular hole and it eventually broke into three pieces.The fractal dimension and fracture density of the prefabricated fractured specimens in the 0°strike are much lower than those in the 45°and 90°strikes.When the spacing is constant,the number of cracks after the failure of the specimens in the strike range of 0°to 30°is similar,and the difference is within 8%,while the difference in the number of cracks in the specimens in the strike range of 45°to 90°is less than 10%.However,their number of cracks increases by 30.4%44.2%compared with the specimens in the 0°30°strikes.The prefabricated cracks in the 45°90°strikes facilitate the fracture of the specimen,while the spacing between the crack and the hole has little effect on the fracturing effect of the specimen.In the strike range of 0°30°,the prefabricated cracks play a shielding role and hinder the fracture of the specimen.This shielding effect is significant within 2 times the equivalent radius,and it disappears when the radius is greater than 2 times the equivalent radius.