Experimental And Finite Element Simulation Of Directional Expansion Cracking Behavior Of Rock-Like Material With A Single Hole

Explosive blasting is a common method of crushing construction in engineering constructions,but it is often limited by the sensitive area of engineering.Therefore,static rock breaking technology is gradually developed.The vibration induced by borehole dilatation and rock breaking is small,which does not exert the influence on the surrounding high-rise buildings,tunnels,reservoirs and subway structures.At present,borehole dilatation and rock breaking have been widely used in engineering practice,but there is little research on rock breaking mechanisms.Therefore,it has important guiding significance to the study of borehole dilatation and rock breaking.In this paper,the self-regulating splitters were adopted,and concrete was taken as rock-like material.Through laboratory dilatation test and numerical simulation,the peak load characteristics and crack propagation law of specimens under different hole shapes and grooving methods were analyzed under the loading of the splitter.Particularly,the stress distribution around the hole was further studied.The following laws were found.(1)Compared with the specimen of circular holes,the peak load of the specimen with elliptical holes,rectangular holes and rhomboid holes decreased to varying degrees.When the specimen shape and the ratio of hole are the same,the peak load of specimens containing diamond hole are less than those of specimens with elliptical hole and rectangular hole.Under the same hole shape,the peak load of both elliptical and rhomboid specimens decreases with the increase of the ratio of long and short axes(diagonal lines).For rectangular cavity specimens,the peak load increases first and then decreases with the increase of side length ratio.(2)Compared with the ungrooved specimens,the peak load of grooved specimens decreased to varying degrees.When the groove angle is constant,the decreasing amplitude of specimen peak load decreases with the increase of the grooving number,and that is,?F(double notch)>?F(three notch)>?F(four notch).When the number of groove keeps constant,the decreasing amplitude of specimen peak load increases with the increase of groove angle,and that is,?F(30~o)<?F(45~o)<?F(60~o).The two-factor analysis of variance shows that changing the groove angle has a significant effect on the specimen peak load,while changing the groove number has no significant effect on the specimen peak load.(3)Compared with the circular cavity,the tips of elliptical cavity,rectangular cavity and rhomboid cavity all have a guiding effect on the crack initiation on the specimen.Among them,the crack propagation of specimen with circular cavity is relatively random,the specimen with elliptical cavity or diamond cavity produces two macroscopic cracks along the tips of the long axis(long diagonal),while the specimen with rectangular cavity produces two or four cracks along the tips of the rectangle.For the same hole types,the guiding effects of elliptic or rhomboid hole on the crack increase with the increase of the ratio of long and short axes(diagonal lines),while the guiding effect of rectangular hole does not change significantly with the change of the side length ratio.In terms of crack guiding effect,rhomboid hole is better than elliptic hole,and elliptic hole is better than rectangular hole.(4)Notch has a guiding effect on the initiation of crack,and at least one crack in V-shaped grooving specimen initiates along the grooving.When the grooving angle is constant,the guiding effect of grooving increases first and then decreases with the increase of the grooving number.Namely,the three-grooving specimens show the most obvious crack guiding effect,the number of cracks produced by the specimen along the grooving is the most,and the concrete crushing effect is the best.At the same time,the effect of changing groove angle on crack guidance is limited.(5)The extended finite element method was used to simulate the cracking on the specimens,finding that the crack propagations of the numerical modelling are in good agreement with the laboratory test results.Stress distribution around the hole shows that stress concentration occurs at the tips of the hole when the hole shape is changed or grooves are cut around the hole.Moreover,the variation trend of the stress concentration degree is consistent with the peak load variation trend of laboratory dilatation test specimens.