Study On The Attenuation And Influencing Factors Of Dominant Frequency Induced By Blasting Vibration

As an economic,efficient and widely applicable construction method,engineering blasting is widely used in the excavation of dam foundation,slope and tunnel of water and hydropower projects.It brings convenience and economic benefits,but also induces a series of harmful effects.The prediction and control of blasting vibration,which is the first public hazard,is the focus of people's attention.At present,peak particle vibration velocity and blasting vibration frequency are the two most important criteria for evaluating blasting safety.Due to the complexity of the frequency components and their variation rules of blasting vibration signals,the study on the prediction of the dominant frequency of blasting vibration are much less than that of the mature and in-depth study on peak particle vibration velocity.Therefore,the study on the attenuation and influencing factors of dominant frequency induced by blasting vibration is of great positive significance for effectively controlling the harmful effects of blasting vibration.Aiming at the prediction and control of the dominant frequency of blasting vibration,a systematic study has been carried out by combining theoretical analysis,numerical simulation and field experiments.The relationship between the dominant frequency of blasting vibration and structural response has been analyzed.The spectrum characteristics of the frequency of blasting vibration and its influencing factors have been studied,and the relationship between the dominant frequency and the development of plastic zone has been revealed.On this basis,the attenuation formulas of dominant frequency for tunnel drilling and blasting excavation and cylindrical explosive source are proposed respectively,and the proposed formulas have been verified and discussed by fitting of the dominant frequency obtained in field tests.The relationship between blasting vibration frequency and structural response is revealed by the calculation and analysis method of structural dynamics.The results show that with the increase of the ratio of exciation frequency to system natural frequency,the ratio of zero-crossing dominant frequency to system natural frequency increases.When the exciation frequency approaches the natural frequency,the peak frequency of vibration is mainly controlled by the natural frequency.When the exciation frequency is far away from the natural frequency,the peak frequency of vibration is mainly controlled by the exciation frequency.Based on the analytic solution of stress wave induced by spherical cavity in infinite rock mass,the analytical expressions of natural frequency and the velocity amplitude spectrum of rock mass system under the excitation of spherical blasting source are deduced.Based on the calculation expression of velocity amplitude spectrum,the effects of blasting load peak,load rising time,load duration,distance and radius of elastic cavity on the dominant frequency of blasting vibration are analyzed respectively.The results show that,in addition to the peak explosive load,other factors have influences on the dominant frequency of blasting vibration to varying degrees.The numerical models of spherical charge and cylindrical charge are established by numerical simulation method.The results show that both zero-cross dominant frequency and fourier dominant frequency decreases with the increase of elastic cavity radius,and the dominant frequency of blasting vibration increases linearly with the increase of the ratio of rock longitudinal wave velocity to the elastic cavity radius C _P/a.The changing rules of dominant frequency of blasting vibration induced by spherical blasting source is similar to that of natural frequency of rock mass damper system under spherical excitation.Charge weight does not directly affect the dominant frequency of blasting vibration,but changes the main frequency of blasting vibration by changing the radius of elastic cavity formed by blasting.Based on the analysis method of structural dynamics and dimension analysis,the attenuation formula of dominant frequency induced by tunnel blasting vibration,which is suitable for the approximate spherical blasting source,is deduced.The validity of the formula is verified by fitting of the dominant frequency obtained by numerical calculation and field experiments.On this basis,two parameters,elastic cavity radius a and charge weight per delay Q,are compared.The results show that the elastic cavity radius a is better than charge weight Q in fitting the attenuation law of the dominant frequency obtained by tunnel blasting and excavation.Based on the theoretical solution of elastic spherical wave propagation and the method of dimensional analysis,the elastic cavity formed by cylindrical explosive source blasting is equivalent to the explosive source.Referring to the modification of cylindrical wave theory in the attenuation formula of particle peak vibration velocity,the attenuation formula of dominant frequency by cylindrical charge blasting is derived.The formula is verified by fitting the dominant frequency obtained by numerical calculation and field experiments.By comparing and analyzing the fitting results of the measured radial vibration and vertical vibration,it is proved that different kinds of seismic wave components will affect the attenuation of the dominant frequency of blasting vibration.Although the attenuation formula is derived from the radial vibration,a favorable correlation coefficient also can be obtained for the fitting of the measured blasting vibration.On this basis,by comparing other existing attenuation formulas of dominant frequency with the proposed formula by this paper,the results show that the fitting correlation coefficients of the attenuation equation proposed in this paper are better than other existing formulas,which can not only obtain a good fitting correlation,but also more concise in form and easy to use.