| With the development of the national economy,people's demand for mineral resources and infrastructure construction is increasing.As a fast,economical and efficient excavation method,blasting is widely used in engineering practice.However,in the process of blasting and excavating open-pit mines and urban underground spaces,blasting vibration,which is the most harmful effect of blasting,is a problem that cannot be ignored.And the blasting vibration has an elevation effect with the increase of the elevation difference.Therefore,it is of great theoretical significance and practical engineering value to explore the mechanism of elevation effect and attenuation law of blasting seismic waves in the propagation process,and to seek economical and reasonable blasting mining technology on the basis of ensuring the safety of the final slope and adjacent buildings.In this paper,theoretical analysis,model test,numerical simulation,field monitoring and other methods are used to study the vibration elevation effect of bench blasting.A geometric model of the steps is established and the reflection law of vibration waves on the free surface of the steps is analyzed.Concrete models with different step heights and inclination angles were poured,and the influence of step height,inclination angle and explosive amount on the elevation effect was studied.A numerical model of the steps was built,and the dynamic response characteristics of single-hole and multi-hole blasting were analyzed.Field monitoring and statistical analysis of blasting vibration are carried out.The prediction and evaluation method before blasting vibration and the calculation method of safe charge are proposed,and verified in the field engineering.The main research results obtained in the thesis are as follows:(1)The elevation effect of blasting vibration is actually caused by the reflection and superposition of blasting vibration waves on free surfaces.At the same time,by simplifying the vibration velocity ratio of the measuring points with the same horizontal distance from the explosion source but different vertical distances,combined with the Sadowski formula,a formula suitable for predicting the peak vibration velocity of the step terrain is derived.Furthermore,the concepts of step positive formula and step negative formula are proposed.(2)Through the similar model blasting test,it is concluded that the existence of positive and negative elevation steps mainly attenuate the blasting vibration,and an amplification effect appears at individual measuring points.?At the positive stage,the larger the explosive quantity,the more obvious the amplification effect.The higher the height of the steps,the farther the position of the maximum value of the ratio between the vibration speed of the steps and the ground vibration speed,is from the explosion source.Steps with a slope of 60° are more conducive to the elevation amplification effect;? In the negative step,the step closest to the blasting source has the most obvious attenuation effect on blasting vibration,and the greater the height of the step,the more obvious the attenuation.As the step inclination angle decreases,the attenuation effect on the vibration velocity gradually weakens.(3)Through the numerical simulation of single-hole and multi-hole blasting,it is revealed that during the process of blasting vibration propagating on the step slope,the measuring point of the maximum effective stress and the measuring point of the maximum vibration velocity are not necessarily the same.That is,the maximum effective stress and the peak vibration velocity are not synchronized.When the delay time is 6ms,the blasting vibration velocity magnification is the largest.At the same time,the effect of elevation magnification is more likely to appear on the positive step,and it appears earlier on the negative step.(4)Through the analysis of the vibration velocity of the field monitoring,the relative error of the step formula is 36.8%,and the accuracy of the step formula in predicting the vibration velocity of blasting vibration is higher than that of the Sadowski formula(58.2%).Compared with positive elevation,negative elevation is more helpful for attenuation of blasting vibration.The area where the magnification effect is obvious is that the positive elevation is at a horizontal distance of 500-600m,the vertical distance is 50-100m,and the negative elevation is at a horizontal distance of 100-500m,the vertical distance is 60-80m.The main vibration frequency of positive elevation is mainly concentrated in 5-15Hz,and the main vibration frequency of negative elevation is mainly concentrated in 10-20Hz.Positive elevation is more helpful to suppress and weaken high frequency harmonics.(5)Based on the normal distribution function,a prediction and evaluation method of blasting vibration before blasting is proposed,which can quantitatively describe the influence degree of a blasting on the protected target.At the same time,according to the importance of the target facility,a probability algorithm can be used to obtain the maximum single-shot dose.(6)Using the step formula,vibration propagation law,blasting vibration evaluation,and safe charge calculation method obtained from the above research,the blasting plan for the diversion of Jinou Open-pit Coal Mine and the road cutting of Dianzhang Highway was designed.The monitoring results of blasting vibration and the width of house cracks showed that the blasting did not cause damage to the office building of Jin-Ou Open-pit Coal Mine and residential houses near Dianzhang Road.It is proved that the above research results are feasible for bench blasting engineering and have high practical value.The research results of this paper have important theoretical and practical significance for the understanding of the propagation law of bench blasting vibration,the mechanism of elevation effect,the design of open bench blasting,the prediction and evaluation of blasting vibration,and the calculation of safe charge.The paper has 122 pictures,49 tables,and 142 references. |
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