The Characteristics Of Pressure On Borehole Wall For Decoupling Charge

Blasting technique is widely used in infrastructure construction such as water conservancy and hydropower engineering,mining,transportation,municipal administration,etc.Decoupling charge blasting is even more an important means for excavation contouring and blasting effect control.The borehole pressure characteristics of the decoupling charge blasting directly affect the damage range of the rock mass and the contour forming quality.It is the key parameter for the design of contour blasting and the numerical simulation analysis of the non-fluid-solid coupling blasting.Therefore,it is of great theoretical significance and engineering application value to comprehensively analyze and determine the borehole pressure characteristics of the decoupling charge blasting.The paper combines theoretical analysis,fluid-solid coupling dynamic finite element numerical simulation and explosion test to study the borehole pressure characteristics of the decoupling charge blasting.The detailed research content and results are as follows:According to the mass conservation,energy conservation,momentum conservation equation of the shock wave,as well as the polytropic equation of state and boundary conditions,the interaction process between the air shock wave and the borehole is analyzed in detail and the ratio of transmission pressure p₃ to incident pressure p₁ is deduced.It is concluded that the peak pressure of shock wave in decoupling charge blasting is related to borehole medium condition,decouple coefficient and explosive performance,in which decouple coefficient and explosive performance have a great influence on the peak value of shock wave pressure,while the influence of borehole medium condition is small.Based on numerical simulation of fluid-solid coupling dynamic finite element method ls-dyna,the blast air shock wave increase factor of three rock medium conditions:granite,limestone and sandstone,two kinds of contour blasting commonly used explosives:emulsion explosive and porous granular ammonium explosive,five common contour blasting decoupling charge structures:25/42,25/50,32/76,32/90,32/110,three axial charging coefficient:1.0,0.6 and 0.3 are studied.The results show that the explosion shock wave pressure increase factor of contour blasting is not a constant,and the ranges corresponding to the above conditions is from 6 to 31.The pressure increase factor is related to the characteristics of explosive,medium condition of porehole,decoupling charge coefficient,etc.Among them,the decoupling coefficient and the performance of explosives are greatly affected,and the influence of the rock media condition is small.Statistical analysis of the simulated shock wave peak pressure shows that the ratio of the shock wave peak pressure of the axial decoupled charge to the axially coupled charge is approximately equal to the axial charge coefficient.Based on the simulated shock wave peak pressure,combined with theoretical derivation results and common blasting shock wave peak pressure calculation form,a new type of decoupling charge blasting shock wave peak pressure calculation method is suggested.The indoor explosion container test was carried out to test shock wave peak pressure and verify the accuracy of the suggest calculation formula.Combined with numerical simulation results,existing research results and high-speed photography data of on-site blasting test,the blasting load action time is analyzed.It is concluded that the shock wave action time of the decoupling charge blasting load is about dozens of microseconds,and the time of the explosive gas action is about 10 milliseconds.