| Drilling and blasting method is universally adopted in various projects of mining rock mass excavation,especially in underground tunnel driving projects such as traffic tunnels,mine roadways,and hydraulic tunnels.In the process of blasting driving of underground tunnel,good cutting blasting effect is the key to realize efficient blasting driving.However,for hard rock mass,the fracture range caused by explosive blasting is limited.Thus,the rock mass in the cutting cavity could not be effectively broken and disintegrated,and it is difficult to be thrown out form the cutting cavity,which ultimately leads to poor cutting blasting effect.To improve the cutting blasting effect of hard rock,a kind of annular slit charge was proposed to directionally strengthen the fracture of rock mass in the cutting cavity.Then,the rock mass in the cutting cavity could be fully destroyed to form the broken rock pieces with reasonable fragmentation and easy to throw,hence achieving good cutting blasting effect.In order to explore the blasting mechanism of annular slit charge,the distribution features of hole wall pressure and the mechanism of directional fracture blasting after annular slit charge blasting were analyzed theoretically.Using the high speed schlieren and shock wave overpressure combined testing system,the propagation characteristics of detonation products and shock wave and the distribution features of explosion pressure were investigated after the explosion of ordinary column charge and annular slit charge with different tube materials in the air field,and the tube material of annular slit charge was optimized and designed.Through single-hole blasting experiments,the difference of explosive strain distribution and blasting crack distribution between ordinary column charge and annular slit charge was studied.Based on the numerical simulation,the distribution features of hole wall pressure and the formation process of guided crack for the annular slit charge were presented intuitively,and the slit width of annular slit charge was optimized and designed.Then,the cutting blasting experiment and field application experiment were carried out to explore the influence of annular slit charge on hard rock cutting effect and the engineering applicability of annular slit charge cutting blasting technique.The main achievements are as follows:(1)The existence of annular slit tube would reduce the hole wall pressure at the non-slit position and increase the hole wall pressure at the slit position.Under the intense impact of strong shock wave,the rock mass corresponding to the annular slit would be destroyed to form a long and narrow fracture zone,which was similar to the annular horizontal guiding crack.Under blasting stress wave,the stress concentration effect would be generated at the tip of the guided crack,which would make the guided crack preferentially extend forward.In the subsequent action stage of explosive gas,a greater stress intensity factor could be produced at the tip of the blasting crack at the annular slit position,thus the blasting crack at the annular slit position could continue to extend preferentially and rapidly.(2)After the explosion of ordinary cylindrical charge,the detonation products and explosion shock wave propagated evenly around the charge center,and the explosion pressure was symmetrically distributed along the charge center,which meant that the explosion energy was evenly distributed along all directions around the charge.In the early explosion stage of annular slit charge,both detonation products and explosion shock wave preferentially propagated outward from the slit position.The existence of annular slit tube would increase the explosion pressure in the slit direction and reduce the explosion pressure in the non-slit direction,which indicated that the annular slit charge had a certain energy gathering effect in the slit direction.The energy gathering effects of annular slit tubes made of different materials are different to some extent.From high to low,SS tube,PVC tube,FRP tube,and PMMA tube were in order.However,after considering the energy gathering effect,usage cost,and safety,the PVC tube was recommended to be used.(3)The explosion strain around the ordinary cylindrical charge was symmetrically distributed along the hole center,while the existence of a annular slit tube could increase the explosion strain in the slit direction and decrease the explosion strain in the non-slit direction.The sharp contrast between the explosive strain distribution features of the two charges confirmed the energy gathering effect of the annular slit charge in the slit direction.After ordinary column charge blasting,three radial blasting cracks were formed around the blasting hole.The radial cracks had no specific propagation direction,and the length of the radial cracks was basically about 100 mm.After the annular slit charge blasting,a horizontal blasting crack penetrating the whole blasting model was formed at the horizontal height of the annular slit.This horizontal blasting crack extended to the edge of the blasting model,and the development degree of the horizontal crack in the slit direction was obviously higher than that in the non-slit direction,which indicated that the crack propagation ability in slit direction was improved obviously.(4)Numerical simulation results showed that the peak values of hole wall pressure were basically the same at the non-slit position,and the peak value of hole wall pressure at the slit position was obviously higher than that at the non-slit position.Because of the high initial pressure on the hole wall at the slit position,the rock mass corresponding to the annular slit would rapidly destroy to form a crushing zone similar to annular horizontal guided crack.With the increase of the extension distance of the annular horizontal guided crack,the width of the guided crack gradually decreased to form the crack tip.Moreover,the optimum slit width was determined to be 4mm by analyzing the variation of hole wall pressure and guided crack length with slit width.(5)When the ordinary column charge was used in cutting holes,the hole utilization rate of cutting blasting was about 75%,and obvious large rock pieces was produced.When the annular slit charge was used in cutting holes,the hole utilization rate of cutting blasting was more than 95%,and the rock fragmentation after blasting was uniform and reasonable.The results indicated that the use of annular slit charge could significantly improve the cutting effect of hard rock.Then the field application results showed that the use of annular slit charge in cutting holes could obviously improve the cyclical footage and hole utilization rate,and prominently reduce the unit consumption of explosive and detonator.It not only accelerated the blasting driving speed of hard rock roadways,but also reduced the blasting driving cost of hard rock roadways.The results proved that the annular slit charge cutting blasting technique had a good applicability in blasting driving of hard rock underground tunnels.Figure 98 Table 23 Reference 212... |
