Numerical Simulation Research On The Effect Of Free Surface Conditions On Blasting Action

The free surface conditions in rock mass blasting play a decisive role in the blasting effect.The use of free surfaces to expand the rock breaking efficiency and decomposition of blasting vibration has always been one of the hotspots in blasting engineering research.However,the reasons for the influence of free surface conditions on the blasting effect have not been systematically reviewed.Mainly through the numerical simulation of dynamic finite element software,the study of different free surface conditions on the crack propagation,fragmentation effect and blasting depth in the blasting effect.Therefore,studying the influence of free surface conditions on the blasting effect can promote the blasting theory and blasting design.The effect of vibration.First,according to the theory of rock mass blasting and fragmentation,the influence of free face blasting stress wave propagation and blasting effect is analyzed,and the energy distribution law of blast shock wave and the theory of blasting line expansion are studied.Fragmentation effect.Research shows that the reflection wave generated by the free surface gradually promotes and guides the development of the fracture zone,and the rock mass fragmentation within the range of the reflection wave of the free surface accelerates.Then,from the energy point of view,the rock fragmentation under the condition of the free surface is analyzed.The mechanism and quantitative study of the influence of the free surface on the parameters of the blasting stress wave showed that the existence of the free surface changed the distribution characteristics of the explosion energy,resulting in an increase in the breaking energy and a corresponding decrease in the energy of the blasting vibration,and the free surface would cause the front end of the blasting stress wave The acceleration of the stress decay and the slower the decay of the front end velocity of the particle also change the loading waveform of the blasting stress wave.With tunnel engineering as the background,the mechanism of the influence of the number of free surfaces on the blasting effect is studied through numerical simulation.The research shows that the number of free surfaces significantly affects the vibration speed of the tunnel structure and surrounding rock during blasting and excavation.For the ratio of section excavation and excavation,the larger the number of free surfaces,the smaller the pre-vibration velocity caused by blasting.It is recommended that the influence of the number of free surfaces should be considered in the blasting design.Combining with the fact that water often accumulates in the working face during vertical shaft driving and blasting,the influences of two types of free surfaces,anhydrous and with water,on the blasting effect and vibration speed are analyzed.It shows that the existence of free surfaces will accelerate the attenuation of the blasting shock wave,thereby affecting the demolition.The rock effect has an impact.And free area water has an attenuation effect on the blasting vibration velocity,and the specific value of its attenuation is related to the wave impedance of water and rocks.Through the numerical experiments of straight,concave and convex free surface blasting,the crushing effect and efficiency analysis of the three are compared,and it is found that the blasting broken volume when the convex free surface is the largest,and the influence of the curvature of the free surface on the blasting broken volume is further analyzed.For this reason,a concept of critical curvature is proposed.When the curvature of the free surface is higher than the critical curvature value,the cavity expansion crushing zone near the charge pack and the reflection stretching wave forming failure zone can be interchanged.It is clear that the curvature parameters should be considered when designing the blasting parameters.,Appropriate modification of the free surface shape can improve the blasting effect.