Experimental Study On Dynamic Caustics Of Smooth Blasting Parameters In Roadway Excavation

The effect of blasting parameters on the blasting effect is studied through the double-hole blasting test with the dynamic caustics test system.Use plexiglass material(PMMA)to make 5 sets of PMMA test panels with a diameter of 5mm for single-hole initiation experiments and 8 sets of PMMA test panels for double-hole initiation tests to study crack formation and blasting fragmentation effects under blasting load,and use uncoupled charges On this basis,set different hole distances and light blasting layer thicknesses,and use the controlled variable method to design the experiment to study the effect of hole distance changes and light blasting layer thickness changes on the smooth blasting effect.Combine the high-speed camera to carry out the explosion process.Shooting and capturing,through the comparison and analysis of the post-explosion effect of the specimen and the characteristic quantity represented by the focal speckle.Through single-hole initiation experiments,it is concluded that the change of the hole distance mainly affects the penetration ability of the cracks between the holes,the expansion ability of the cracks on the hole center line and the change of the crushing zone;the change of the thickness of the optical blast layer mainly affects the blast hole The number and length of crack propagation between the free surface and the infinite medium direction.Through the double hole initiation experiment to study the effect of the hole distance and the thickness of the light explosion layer on the crack propagation mechanism,it is found that when the hole distance increases,the penetration capacity of the cracks between the holes decreases.When the hole distance is 40 mm,the cracks between the holes show a hooked penetration.When the distance is 45 mm,the crack between the holes presents a linear penetration,when the hole distance is 50 mm and 55 mm,there is a contact type penetration.When the hole distance is greater than55 mm,the crack between the holes does not penetrate;when the hole distance between the two holes on the test piece increases,The length of the crack in the direction away from the adjacent hole gradually decreases,and the diameter of the crushed zone also decreases.Combining the crack penetration effect,the crack length in the direction away from the adjacent hole,and the change rule of the crushing zone range can be obtained.The time-surface blasting has the best seam effect between40 mm and 50 mm aperture;When the thickness of the optical explosion layer increases,the length of the crack in the direction of the infinite medium increases,so the degree of damage to the material in the direction of the infinite medium also increases.In the double-hole initiation experiment,it is found that the thickness of the optical explosion layer is35 mm.A crack penetration was formed between the free surfaces and a 6mm under-excavation part appeared.At 40 mm,a crack penetration was formed between the blast hole and the free surface and an over-excavation depth of 8.5mm was formed.When the thickness of the optical blast layer is 45 mm,the gun There is no crack penetration between the hole and the free surface and there is no over-under-excavation phenomenon.Therefore,combining the blasting fragmentation range obtained from the single-hole initiation experiment,it can be obtained that the thickness of the light blasting layer is set between 50 mm and 55 mm.The time surface blasting effect is better.In summary,the larger the hole distance,the weaker the crack penetration between holes,and the weaker the interaction between blast holes.When the thickness of the optical blast layer increases,the crushing effect of the main blast zone is weakened and the damage to the material in the direction of the infinite medium is weakened.Increased,the hole pitch is set between 40 mm and 50 mm,and the thickness of the light blasting layer is set between 50 mm and 55 mm.The surface blasting effect is better.