Study On Influence Law And Prediction Methed Of Pre-splitting Crack Parameters On Vibration-reduction Effect

Blasting vibration has a serious impact on the normal production activities of open-pit mines and the surrounding environment,so reducing the effect of blasting vibration has become an important problem that needs to be solved urgently in the practice of blasting engineering.Pre-split blasting is widely used in deep-hole bench blasting in open-pit mines because of its good shock absorption and shock isolation effect.The seismic waves generated after blasting encounter pre-splitting,reflection,refraction and other phenomena occur,which effectively reduces the damage to the rock and soil.In this paper,the pre-splitting crack parameters is taken as the research object to study the response characteristics of the vibration reduction effect to the multi-parameters of the pre-splitting crack deeply and systematically,and a method for predicting the vibration reduction effect of the pre-crack parameters is proposed,which is useful for guiding the design of pre-spl itting blasting and reducing blasting vibration.Harm is of great significance.The characteristics of blasting seismic waves are analyzed theoretically from amplitude,frequency,and duration of vibration,and by studying the propagation of seismic waves when entering the pre-splitting crack at different angles,the relationship between effect ofvibration reduction and the wave resistance of the propagation medium as well as the width of the pre-splitting crack is obtained.Through indoor physical simulation tests,it is found that the width of pre-splitting crack increases from 2cm to 4cm,the downward trend of the velocity attenuation curve is steep,and the damping rate monitored at each measuring point increases significantly;afterwards,the width continues to increase,and the downward trend of the velocity attenuation curve is gentle.With the increase of the length and depth of the pre-splitting crack,the shock absorption rate of each monitoring point shows an increasing trend,and the effect of vibration-reduction is improved.At the same time,with the increase of the distance range behind the crack,the degree of vibration change is weakened by the interference of the pre-splitting crack,and the influence of the increase of the crack parameters on the seismic reduction effect decreases.Through AUTODYN numerical simulation,the sensitivity of each parameter of the pre-splitting crack to the damping effect in descending order is:width,length,and depth.The change of width plays a major role in controlling the damping effect.Traditional neural networks such as BP and ELM are optimized by particle swarm optimization.Width,depth,length of pre-splitting crack,fracture source distance and impact energy are used as the influencing parameters,and the shock absorption rate is evaluated as the index.A prediction model of vibration reduction effect combining particle swarm algorithm and neural network is constructed.The comparison and analysis of the prediction results show that the prediction results of the PSO-ELM model have the highest accuracy and the lowest error.The application of this predictive model has important theoretical value and practical significance for blasting vibration control.