At present, the mainstream blasting method is controlled blasting, which includes directional blasting, smooth blasting, splitting blasting, and millisecond blasting [6-8].
Air-uncoupled charging can be used in peripheral eye blasting in smooth blasting to reduce the surrounding rock damage.
where [[rho].sub.0] represents the density of explosive (g/[cm.sup.3]); D represents explosive velocity (m/s); y represents the isentropic exponent of explosive, usually takes 3; [d.sub.c] represents the charge diameter; [d.sub.b] represents borehole diameter; [l.sub.e] represents the length of blast holes; [l.sub.b] represents the length of charge column; here smooth blasting holes take [l.sub.e] = 0.6[l.sub.b] and auxiliary holes take [l.sub.e] = 0.8[l.sub.b]; n represents pressure increasing factor when the detonation gas expansion collides with hole wall, n = 8-11, and it takes 10 for emulsion explosive.
Electronic detonator is used for initiation delay to reduce the blasting vibration and improve the effect of rock fracture in many engineering experiments [18,19], and at present the minimum delay has already reached 1 ms, so I used MS1 and MS9 electronic detonators to achieve initiation delay for auxiliary blasting holes and smooth blasting holes.
Taking the blasting excavation of the protective layers of rock-anchored beams in the underground main power house of the right bank of the dam as an example, the blasting excavation of protective layers of rock-anchored beams drills the vertical smooth blasting holes, oblique smooth blasting holes, and auxiliary blast holes manually in the rate of 20.4 m excavation length each time.
The blasting load is exerted on lines of centers of auxiliary holes first and then on lines of centers of smooth blasting holes.
Due to the fact that the V-shape grooving has been done on part of smooth blasting holes in the blasting excavation process of rock-anchored beam on site, two-dimensional crack forming model of blast holes is added in order to compare the effect of crack forming of grooved blast holes with that of circular blast holes.
In 1950s, the smooth blasting method has been put forward in Sweden.
However, the effect of the smooth blasting in the left side is not so good.
Correspondingly, there is less phenomenon of over excavation around the tunnel, and the smooth blasting effect is improved.
Du et al., "Reasonable smooth blasting factor used in tunnel," Journal of Chongqing University: Natural Science, vol.