Numerical Simulation Research On Blasting Of Hollow Hole And Wedge-shaped Cutting

In the tunnel cut blasting technology,wedge cutting has many advantages,such as smaller number of drilling hole and low requirements,better blasting effect and larger groove cavity generated.The layout of the holes in the cut blasting can not only provide the expansion space for the broken rock,but also make use of the free surface effect of the empty hole to improve the internal stress distribution in the rock mass,thereby increasing the recycling footage.In order to improve the rationality of parameter setting of hollow hole in wedge cut blasting,finite element analysis software LS-DYNA was used to simulate wedge cut blasting with empty hole.The influence of different empty hole conditions on the distribution of stress field in wedge cut blasting was analyzed.The main research contents of this paper include:(1)According to the classic theory of explosive mechanics,the rock fragmentation and throwing mechanism during wedge cutting blasting are analyzed.The distribution of stress field in the rock under different void diameters is discussed.(2)The finite element software LS-DYNA was used to build a two-dimensional wedge undercut blasting bottom calculation model.The broken through process at the bottom of the wedge cut blasthole was simulated by single blasthole and multiple blasthole.By changing the diameter of empty hole,the distribution of the maximum principal stress around the empty hole under different diameters and the crack status are analyzed.The results show that the growth rate of reflection tensile stress near the hole becomes slower when the diameter of the empty hole exceeds 2 times the diameter of the blasthole under the action of single hole.Under the effect of multiple holes,due to the superposition of stress waves,the two holes with smaller hole spacing first penetrate and the stress superposition zone will induce the propagation direction of the cracks throughout.As the diameter of the empty hole increases,the region of greatest concentration of the principal stress near the empty hole becomes smaller.(3)The calculation model of three-dimensional wedge cut blasting with empty hole is established.The simulation of cutting blasting under different hole diameters and depths is analyzed.The influence law of void diameter and depth on the distribution of explosion stress field is found.The results show that the size of the stress concentration zone near the hole fluctuated and the stress concentration intensifies first and then decreases in the hole wedge cut blasting.The larger of the hole diameter,the more obvious of the phenomenon.When the ratio of depth of empty hole to depth of cut is in the range of 0.92-1.0,the increase of depth of empty hole will weaken the stress peak of the bottom rock.(4)The calculation model of wedge cut blasting with empty hole with bottom charge structure is established.Compared with the calculation model without bottom charge structure,charge blasting at the bottom of empty hole can obviously improve the stress field strength at the bottom of cut and it also can overcome the rock blasting clamping force of the bottom resulte in a better wedge cut cavity effect.