Research On Dynamic Evolution And Crack Propagation Law Of Rock Bidirectional Cumulative Tensile Blasting

The research and application of bidirectional cumulative tensile blasting technology originated in World War I,and it was mainly used in weapons and equipment at the beginning.With the development of blasting technology,bidirectional cumulative tensile blasting was gradually applied to geotechnical engineering,blasting molding and other fields.Because of the more and more extensive application of bidirectional cumulative tensile blasting in underground blasting engineering,slope blasting engineering and military blasting,the requirements for the connectivity of cracks and the linearity of cracks in the direction of shaped blasting are also continuously improved.However,at home and abroad,the focus of research on rock directional fracture focuses on slit-cut blasting and slot-cut blasting.Moreover,underground geological conditions are complex and changeable,and the rock mass in the range of pre-splitting is not composed of a single rock layer,but a combination of soft and hard rock layers,which causes great difficulties to the effect of rock directional blasting.The shaped device has a great influence on the effect of bidirectional cumulative tensile blasting.However,at present,the influence law of shaped hole on the effect of shaped charge blasting is not very clear,which brings some troubles to the further optimization of the shaped charge device and also causes some obstacles to the wide application of the bidirectional cumulative tensile blasting technology.This project through the theoretical research,numerical simulation and experimental research,to reveal the dynamics process of bidirectional cumulative tensile blasting which can stretch blasting and the radial and axial parameters,optimization design,design of radial and axial evolutionary dynamics of shaped blasting of rock mass and the investigation of the rule of crack extension,has important scientific significance and practical significance.The main research contents of the project include the following aspects:(1)By means of theoretical analysis,the dynamic process of bidirectional cumulative tensile blasting is divided into three stages,and the dynamic evolution process of bidirectional cumulative tensile blasting in these three stages is deeply analyzed.The dynamical action process and the formation mechanism of directional crack of bidirectional cumulative tensile blasting are expounded.(2)By means of theoretical analysis,numerical simulation and field test,the filling medium with axial parameters in bidirectional cumulative tensile blasting is studied.The results show that the energy transfer efficiency of water is much higher than that of air,and the cumulative effect of water(the ratio of the peak stress in the direction of accumulated energy to the peak stress in the direction of unaccumulated energy)is better than that of air.(3)This paper used theoretical analysis and numerical simulation to study the influence of the energy angle on the crack propagation law in the energy-concentration direction.It was found that the energy release rate in the direction of energy accumulation after blasting was the main determinant of crack propagation and bifurcation in the direction of energy accumulation,and it decreased with the increase of the shaped energy angle.When the energy release rate in the direction of energy absorption exceeded a certain critical value,the stress intensity factor K at the crack tip would be affected by the impact load more than the bifurcation toughness K_B,resulting in bifurcation of the crack in the direction of the energy.The SPH method was used to simulate and analyze the energy blasting of four different shaped energy angles.(4)This paper took the coal-containing composite roof of the 12201 working face of Halagou Coal Mine as the engineering background,and based on the technical principles of roof cutting pressure releasing gob-side entry retaining,comprehensive used of theoretical analysis,field experiments and other means,carried out in-depth research on the shaped energy blasting method and parameter design of the coal-containing composite roof.The results show:Through theoretical analysis,in the process of shaped energy blasting,the air column in the hole can reduce the peak blast pressure,which can effectively prevent the weak surrounding rock in the hole from being damaged in the non-cumulative direction and enhance the pre-splitting effect.During detonation at the bottom,the instantaneous pressure in the blast hole is lower than that of detonation at the top,and the action time of blast pressure is longer than detonation at the top.When the buried depth of the explosive(near the blast hole)is less than the critical depth,a"V"-shaped blasting funnel will be formed after the rock blasting,and the critical depth is proportional to the charge.Besides,field tests have shown that when shaped energy blasting is carried out on soft and hard rock formations,the stemming separation in the shaped energy tube at the interlayer position can ensure the directional pre-cracking effect of hard rock,while effectively avoiding damage to the weak rock formation in the non-cumulative direction.