Study On The Influence Of Smooth Blasting Parameters On Blasting Crack And Fragmentation

Smooth blasting technology plays a great role in reducing the damage of surrounding rock and maintaining the stability of surrounding rock.However,with the development of smooth blasting technology,the requirement for the effect of smooth blasting is getting higher and higher.How to reduce the damage of surrounding rock,maintain the stability of surrounding rock and slope and control the fragmentation after smooth blasting so that it can meet the requirements of engineering is the key to improve the quality of smooth blasting.Tunnel smooth blasting often occurs in a large range of smooth blasting layer is broken and collapsed,which brings difficulties to the loading and transportation of follow-up projects.At the same time,large-scale secondary blasting also affects the construction safety and increases the cycle operation time.Therefore,exploring the distribution characteristics of blasting cracks in smooth blasting and the formation mode of blasting fragmentation has a positive promoting role and practical significance in reducing the fragmentation of smooth blasting and enriching the theory of smooth blasting.In this paper,the influence of smooth blasting parameters on blasting crack and its fragmentation is discussed by theoretical analysis,model test and numerical calculation.The results show that: The uncoupling coefficient can significantly reduce the damage to surrounding rock.When the radial uncoupling coefficient is 2,there is basically no macro damage to the wall of surrounding rock.The spacing of blasting holes,the minimum resistance distance and the length of blocking section can affect the maximum size of blasting fragmentation.When the resistance distance is small,the maximum size of blasting fragmentation on cross section is mainly determined by the spacing of blasting holes,and the maximum size of blasting on vertical section is mainly determined by the length of blocking section.Increasing the borehole spacing and reducing the resistance distance within a certain range can make the block size distribution more uniform and reduce the maximum block size.The main factor affecting blasting fragmentation distribution is linear charge density,followed by borehole spacing,and the uncoupling coefficient has the least effect.Charge quantity and borehole density coefficient can not completely determine blasting fragmentation distribution.Blasting fragmentation distribution is also affected by other important factors.In the direction of the borehole connecting center line,the stress wave will superimpose and form a higher effective stress,which will decrease with the increase of the borehole spacing and the cracks first appear from the borehole wall rather than from the midpoint of the borehole connection line.When the hole spacing is 70 cm,the effective stress of the element near the midpoint of the borehole connecting center line under the action of stress wave is only 1.42 MPa,which is less than the tensile strength of the rock and will not form a through crack.The stress wave will superimpose in the direction of free surface,and the peak value of effective stress will decrease with the increase of the minimum resistance distance.Its maximum value is 2.92 MPa.Spallation may occur only when the resistance distance is 40 cm.Therefore,the stress peak value superimposed near the free surface is less than the tensile strength of the rock,and no sheet fall will occur.The results show that the spacing between holes and the minimum resistance distance can affect the propagation and fragmentation of blasting cracks.Therefore,the research in this paper has a certain reference value for the design of blasting parameters.