Study on the effect of slit length of borehole on blasting effect

Abstract

The dynamic caustics system combined with numerical simulation is used to study the effect of the slit in the borehole on the blasting effect. The result show that: slit blasting of the borehole has a significant directional fracture effect when compared with ordinary blasting, the length of cracks in the slit direction is significantly larger than that of ordinary blasting, and the length and number of cracks in the non-slit direction are significantly smaller than that of ordinary blasting. The slit in the borehole wall causes the blast energy to be released mainly in the slit direction and suppressed in the non-slit direction. Crack inhibition zone exists at the root of slit in the borehole wall. Once blasting produced the direction cracks in the slit direction, the surroundings of the blast hole wall will not produce cracks. Slit blasting can inhibit cracks near the slits, so as to achieve the purpose of controlling the direction of rock fracture. As the slit length increased, the major crack propagation length of the slits decreased before increasing. When the slit length increased to 5mm (diameter to length ratio of 1.2), the crack propagation length was the largest, then the slit length continued to increase, the crack extension length did not change much. With the increase of the slit length, the peak value of the slit main crack propagation stress intensity factor and the peak value of the velocity show the trend of decreasing and then increasing, and the two peak values are the lowest when the slit length is 3 mm. The horizontal incident tensile wave reflected by rock mass defects and blasthole unloading waves increase the stress intensity factor and crack propagation rate, promoting crack propagation. Considering the blasting effect, the cost and time of drilling slits, it is more appropriate to choose a slit length of 0.5mm (diameter to length ratio λ is 12). The research results provide a certain significance of guidance for the slit blasting of the borehole wall in practical engineering.