Pre-splitting Blasting Test Research With Precise Time Delay (single) Hole One Shot

To study the influence law of change of blasting parameter in presplitting blasting effect and shaped crack mechanism of presplitting blasting,presplitting blasting test was carried out by preparing C25 plain concrete model on the test field.Meanwhile,the influence law of coupling coefficient?,maximum single fire dynamite Q_max,inter-hole delayt_k and guide hole with or without inter-hole for presplitting blasting effect was studied.Besides,the statistics of indexes including half-hole rate,pre-cracking width and longitudinal wave velocity of model was implemented.The presplitting crack propagation during model bursting test was observed through high speed photography system.The stress at center line of blast hole was tested by combining the dynamic strain test.Thus the propagation and crack forming mechanism of presplitting crack was obtained.In the end,the linear charge densityQ_l was further studied by combining BHG’s field test of presplitting blasting zinc and indium strip mineThe study on model test showed:half-hole rate is increased along with the increase in non-coupling coefficient and maximum single fire dynamite and the tendency of increase is gradually mitigated;The presplitting crack width is increased along with the increase in maximum single fire dynamite.Meanwhile,the damage to the model is also severer but it is reduced along with the increase in non-coupling coefficient;when the inter-hole delay is 12ms,the half-hole rate and width of presplitting crack is larger than that obtained under other delay time,and the presplitting blasting effect is the best.It could be seen from the high speed photography of blasting process that the delay of surface crack of model is18ms from forming to the overall application,the velocity of crack propagation is general 382⁵48m/s..Therefore,the inter-hole delay shall not be larger than 18ms.The existence of inter-hole guide hole will lead to increase in half-hole rate but doesn’t bring about great influence to the width of presplitting crack;The stress is reduced along with the increase in delay time and non-coupling coefficient.When the strain value is 318??⁴23.4??,the presplitting crack forming effect is good.Through analysis on influence of inter-hole delay and non-coupling coefficient on strain through response surface analysis,it is obtained that the non-coupling coefficient 2.91 is the optimal value when the inter-hole delay is 17.18ms.The study on field test shows:the presplitting blasting effect is desirable when No.1 rock emulsified explosive is used and linear charge density is 450g/m and 500g/m.By referring to the mass point vibration equation obtained through study on BHG zinc-indium strip mine and combining the mass point vibration velocity of the field test,the average vibration reduction rate of presplitting blasting is 66.7%and that of presplitting crack is 29.7%,when the inter-hole delay is 12ms,which can provide theoretical basis and guidance for presplitting blasting design.