Research Of Reasonable Millisecond Delay Time With Tunneling Blasting

The effect of millisecond blasting is related to the position of blast hole,the condition of rock and geologic,and others,the selection of delay interval millisecond is the core section of the blasting design.In tunneling minisecond tunneling,the research results about the reasonable delay time of tunneling blasting are relatively few in recent years.That the design of the millisecond time still depends on engeneering experience.During the tunnling,it happens a lot that the effect of blasting is not ideal.Therefore, it contains important significance that how to select the millisecond time deliberately.Based on the surrounding rock(grade Ⅲ) excavation blasting engineering of HeXin tunnel,the main research methods include investigation analysis and numerical simulation.From the point of the mechanism of blast rock,according to the physical forming process of blasting funnel gives mathematical model that it could caculation reasonable delay time.The results of study show that:the forming physical process of tunnel rock blasting include detonation stage,crushing stage,throwing stage.The time of detonation stage depends on the detonation velocity and the length of the charge;the time of crushing stage depends on the rock fracture development process;the time of throwing stage depends on the rock throwing speed that are proportional to the size of the explosive energy for throwing rock.Finally the reasonable delay time that be calculated for this project is 39.2ms-164ms.The numerical simulation software, named Midas/GTS,which was used to discuss the vibration influence of tunneling blasting.When simulating the blasting vibration the model does not reflect the hole shape,the blasting load on the bound of crushed zone are equivalently converted and then be loaded on the surface that defined by tunnel excavation contour.Focus on comparative analysis the influence on vibration velocity,stress of surrounding rock and tunnel structure to discuss five kinds of blasting scheme that have different cut hole millisecond time.The results show that when the blasting delay time is 75ms,100ms,millisecond blasting can effectively reduce the vibration velocity of surrounding rock and reduce the damage range of sprayed concrete structure under tension loading.