Study On Dynamic-staic Rock Fracture Mechanism Of Blasting And Blasting Dynamic Behavior Under High Stress Condition

The dynamic and static action effect of blasting stress wave and blasting gas generated by the explosive are the main driving forces for rock fragmentation,and it is always an important topic in rock blasting theory and practice.Until now,there remain different views on respective proportions of blasting stress wave and blasting gas and their distribution in time and space.In addition,the development of rock blasting theory and technology has always served the exploitation of mineral resources.With the development of the deep mining trend of mineral resources,the environment for resource mining is more complicated,and the theory and technology of rock blasting have ushered in new challenges.The high stress condition(in-situ stress)of the deep rock mass affects the distribution of the blasting stress field and the propagation of blast-induced crack,which makes the rock blasting effect significantly different from that of the shallow rock mass.Therefore,the theoretical analysis,model experiments and numerical calculation method are comprehensively used to reveal the action effect of blasting stress wave and blasting gas,and to explain the dynamic blasting behavior under the high stress condition in this dissertation.The main research contents and results are as follows:A workman must first sharpen his tools if he is to do his work well.Combining the digital image correlation method and high-speed camera technology,the experimental system of the high-speed digital image correlation is established,and the feasibility of the experimental system in the study of super-dynamic problems such as blasting is verified.It provides a reliable experimental method for related research in this dissertation.Theoretical and experimental analysis shows that the blasting stress wave is the direct cause of the formation of the crushing zone,and the blasting gas is the main driving force for the formation of the fracture zone.With increased distance from the borehole center,the stress state of medium gradually turns from mainly circumferential tensile to mainly radial compressive in the elastic vibration zone.The results of water jet test show that the blasting stress wave cannot cause the water jet,and the energy of the water jet comes from the work of the blasting gas.Under the combined action of blasting stress wave and blasting gas in a double-borehole blast,the stress component in the direction of the connection line of the two boreholes is mainly compressive,while that in the direction perpendicular to the connection line is mainly tensile.The strengthening effect of blasting stress superposition on the stress component in the direction perpendicular to the connection line(mainly tensile)is significantly less than that in the direction of the connection line(mainly compressive).The results of model experiments and numerical calculations show that crack initiation and propagation in the stress superposition area between the two boreholes have relatively “demanding” requirements for the explosive parameters,rock properties and borehole spacing.Decoupled charge structure is an important method to adjust the action effect of blasting stress wave and blasting gas on rock fragmentation.Decoupling coefficient and filling medium are the two key factors affecting the blasting effect of decoupled charge structure.The numerical simulation results show that,in terms of the peak pressure at the borehole wall under blast loading,the change of the charge structure from coupled to decoupled is a qualitative process.Analysis of model experimental results indicates that for decoupled charge blasting,the filling medium plays a buffering and weakening role in the transmission of blasting energy,which significantly inhibits the formation and development of the crush zone and reduces the damage degree of the entire blasting zone.The effect of different filling media on the fracture zone and elastic vibration zone shows significant differences.Choosing a reasonable filling medium and decoupling coefficient can make better use of the action effect of blasting stress waves and blasting gas,which is conducive to the formation of more and longer blast-induced cracks,increasing the range of fracture zone,and improving the blasting fragmentation effect.The high stress condition of deep rock mass changes the stress state of blast-induced crack and the evolution law of blasting strain.Based on theoretical analysis,a loading device capable of coupling static stress and blasting stress is designed,and the model experiment is performed to simulate the dynamic response of blasting in deep rock mass under high stress condition.The experimental results show that the static stress field has a guiding effect on the propagation of blast-induced cracks.The larger the static stress,the higher the stress concentration at the crack tip,so that the main crack can propagate along the static stress direction at a higher speed,forming a larger propagation length.Moreover,larger static stress induces a greater fractal dimension of the blast-induced crack,and thus a greater damage degree of the medium.In the fracture zone,the static stress increases the fractal dimension and the damage degree along the direction of static stress,but reduces the fractal dimension and the damage degree perpendicular to the static stress direction.In addition,the static stress field reduces the plastic strain and its decay rate in the peripheral region of the fracture zone.As a kind of directional fracture control blasting technology,slit charge blasting plays an important role in blasting construction of deep rock mass.Theoretical analysis indicates that the stress concentration around the borehole under high stress condition shows a distribution characteristic of “high strength and small area”.This stress distribution characteristic significantly affects the crack initiation and early propagation behavior of the slit charge blasting.When static stress is perpendicular to the slit direction,crack initiation occurs in the zone of compressive stress concentration around the borehole and the crack initiation is relatively more difficult.In the subsequent stage of crack propagation,the action of static stress causes the crack surface to close and crack propagation is inhibited.It causes the energy at the crack tip decays rapidly,eventually reduces the crack propagation time and shortens the crack propagation length.When static stress is parallel to the slit direction,cracks initiate in the zone of tensile stress concentration around the borehole and crack initiation occurs relatively more easily.In the subsequent stage of crack propagation,static stress reduces crack propagation resistance and the energy at crack tip decays slowly.This makes the crack propagation time longer and the crack propagation length larger.In the roadway blasting of deep rock mass,the blasting parameters such as the charge amount of slit charge,the borehole spacing and the slit direction need to consider the effect of the high stress condition of the deep rock mass.Defects such as cracks and voids are unavoidable in natural rock mass.The high stress condition of deep rock mass also has a significant effect on the blasting fracture behavior of rock mass with defects.The results of caustic experiments show that the blasting stress wave plays a leading role in the crack initiation and early propagation of the blast-induced crack at the end of the original crack,while the static stress has an important effect on the crack propagation in the later stage.The vertical static stress causes the blast-induced crack to have a velocity component perpendicular to the original crack.With the increase of the angle between the original crack and the horizontal direction,the propagation time of the main blast-induced crack gradually decreases,the moment for significant shear failure to occur is delayed,but the displacement value along the direction of the original crack gradually increases,and the propagation path tends to be straight.In addition,the theoretical criterion based on the minimum strain energy density factor can well predict and explain the initiation behavior of the compression-closed crack under blast loading.The static stress enhances the degree of shear failure during initiation of the crack and promotes the formation of a larger initiation angle.