Similar Model Test And Numerical Simulation Of High-step Throwing Blasting

To investigate the influence rule of pitch-row,array pitch and inter-row delay time to the high bench casting blast effect,in this paper we deduced the similarity criterion that high bench model blast test should follow using dimension analysis method on the basis of similarity theory.The Mortar similar material was made using raw materials such as cement,quartz sand,and water in designed proportion.A two-row-hole casting blast mortar model was established at test site.In observing bench slope using high-speed photography,the velocity law of slope "bulging" center motion and the velocity field law of slope were analyzed.Ultra dynamic strain test technology was adopted to test signal of blast strain wave in mortar,so that radial and tangential strain waves at different test points were obtained.Finite element program was used to simulate bench model blast under different inter-row millisecond delay times,and to analyze the stress,strain,and time-dependent change law of displacement of feature unit in mortar.The high bench blast model test showed that there existed certain particular holes and array pitches that were conductive to bench model casting blast.When density coefficient of hole m met 1.4<m<1.6,bench model casting blast can achieve better throwout rate.Compared with pitch-row,array pitch had larger impact on the longest cast distance Lm.Lm decreased with the extending of inter-row delay time ?t,and such tendency of decreasing gradually tended to be stable.So,regarding high bench cast blast inHeidaigou open-pit coal mine,the hole distance should be set within 9.5?11m,and the row distance should be set as 7.5m.High-speed photography observation results showed that motion speed of bench slope "bulging" center experienced changing process of "acceleration,deceleration,acceleration,uniform speed,and deceleration".The blast fragment in the middle of bench had the largest casting speed(8.2m/s),while fragments at bench slope top and slop foot had smaller casting speeds(1.7?2.4m/s).Ultra dynamic strain test results showed that in the propagation process of blast strain wave,it will cause both radial and tangential strains of medium.When mortar materials were in tensile fracture,the tension strain peak value reached over 1.6×10-4.According to numerical calculation results,it is suggested to set inter-row delay time between 75?102ms for high bench casting blast of Heidaigou open-pit coal mine.