The Theoretical Study On Distribution Characteristics Of Stress Field In Smooth Blasting

Smooth blasting has the characteristics of smooth excavation contour,effective reduction of overbreak and underbreak,improvement of self-supporting ability of surrounding rock,and ensuring the stability of surrounding rock.It is widely used in transportation,water conservancy,mining and other projects.Due to the insufficient understanding of the mechanism of smooth blasting and the complex characteristics of rock blasting,the blasting effect can not meet the expected requirements in the actual blasting process,which often results in overbreak and underbreak of tunnel surrounding rock.The blasting stress field determines the formation process of blasting cracks,thus affecting the blasting effect.Therefore,it is necessary to study the stress field of smooth blasting in order to reveal the mechanism of smooth blasting in essence and provide reference for related projects.Firstly,the development history and mechanism of smooth blasting are summarized and analyzed.Based on the approximate formula of acoustics and the principle of isentropic adiabatic two-stage expansion of explosive gas,the initial impact pressure and quasi-static pressure of borehole wall under the condition of coupled charge and air uncoupled charge are theoretically analyzed,and the quasi-static pressure of explosive gas in borehole is studied with the theory of thick-wall cylinder.The distribution of quasi-static stress field between adjacent boreholes under different borehole spacing is theoretically analyzed.Secondly,based on LS-DYNA3 D finite element software,the constitutive model and parameters suitable for rock blasting materials are selected,and the dynamic propagation process of blasting stress wave under single-hole charge and double-hole charge is simulated by ALE algorithm.The results show that under the condition of double-hole charge blasting,the stress peak value of the midpoint stress wave between the boreholes is far lower than that at the borehole wall even after superposition;when rock is only under the action of stress wave,cracks begin to expand at the borehole wall,which confirms the deficiency of the theory of stress wave action.Finally,the dynamic stress field under different smooth blasting parameters is studied by using the method of parameter analysis.The results show that the change of borehole spacing and thickness of smooth blasting layer has little effect on the peak stress;when borehole spacing or thickness of smooth blasting layer is small,the superposition effect of stress field is enhanced;when borehole spacing or thickness of smooth blasting layer is large,the superposition effect of stress field is weak;the stress wave can be weakened by using small diameter cartridge in actual blasting process.It can be used to control the damage of surrounding rock and obtain good smooth blasting effect.