Vibration Effect And Safety Control Of Tunnel Blasting Excavation

Blasting vibration has always been a hot issue in blasting safety construction.How to realize effective prediction of blasting vibration and effectively reduce blasting vibration by optimizing blasting scheme has great practical significance in engineering.This article relies on“Tail Water Discharge Channel Project contract Section 2 Works of Wastewater Treatment Plant in the Core Area of Gui’an New Area in the core area of Gui’an New Area”,based on the theme of "vibration effect and safety control of tunnel blasting excavation",field blasting tests were carried out,and vibration of tunnel side wall and surface along the tunnel were monitored respectively.Based on the measured data,the peak velocity of blasting vibration,main frequency,frequency band energy,vibration reduction measures and safety control standards are studied.The main research contents and conclusions are as follows:(1)The lateral wall vibration velocity of the tunnel shows that the horizontal radial vibration velocity is the largest,the horizontal tangential vibration velocity is the second,and the gravitational vibration velocity is the smallest.The surface vibration velocity along the tunnel shows that the gravity direction is much larger than the horizontal transverse and horizontal longitudinal direction.Under the conventional blasting construction,the peak vibration velocity usually appears in the secondary cut or the primary auxiliary hole,which is between 005 s and 0.13 s.It mainly comes from the secondary cut blasting or the superposition of the secondary cut and the primary auxiliary hole blasting vibration.Therefore,the cutting section is the key to vibration control,and the wave superposition between the vibration wave produced by the second cutting hole and the first auxiliary eye should be avoided.(2)Based on the measured data,the predictive formulas are fitted by using the Sadovsky formula model,the USBM model,the Indian model and their common basic formulas.Fitting degree shows from high to low as follows: basic formula forecasting model,Sadovsky Formula forecasting model,USBM forecasting model,India forecasting model.Among them,the fitting effect of Sadovsky formula is very close to the basic formula.The comparison between the peak vibration velocity of the inner wall of tunnel and the peak vibration velocity of the surface along the tunnel shows that the maximum vibration velocity of the surface along the tunnel is about 1.25 times of the maximum vibration velocity of the side wall of tunnel under the same blasting parameters and blasting distance.Considering the randomness of blasting vibration,the relative error of predicting vibration velocity(REBVV)is defined,by introducing the theory of normal distribution,the prediction model of vibration velocity of tunnel side wall and surface along the line is obtained.(3)The blasting vibration signals are transformed by Fast Fourier Transform(FFT)and Hilbert-Huang Transform(HHT).In the range of 25-100 m from the explosion source,the frequency is concentrated in 50Hz-300 Hz,and the main frequency is concentrated in 50Hz-150 Hz.The relative error of main vibration frequency prediction(REMVF)is defined,and the normal distribution theory is introduced to obtain the prediction model of the surface in the tunnel and along the tunnel.The correctness of the prediction distribution is verified based on the "3 σ criterion".Based on the Intrinsic Mode Function(IMF)obtained by Empirical Mode Decomposition(EMD),the actual blasting delay is identified by the envelope of Intrinsic Mode Function(IMF).Based on the HilbertHuang Transform(HHT),the effects of detonation center distance and the amount of homogeneous explosive on the energy ratio in different frequency bands were studied.(4)Based on the actual situation of the project,the vibration reduction measures of "double V-cut in two-stage large jump section" are put forward,and the vibration reduction mechanism of double V-cut in two-stage large jump section is explained from three angles of "providing free surface","reducing maximum single-stage charge" and "avoiding superposition of vibration signals in different sections".The influence of optimization on the prediction formula of blasting vibration velocity is mainly manifested in K value,which is about 65% before optimization.The three-dimensional timefrequency spectrum of blasting vibration signals before and after optimization is obtained based on Hilbert-Huang Transform(HHT).The results show that the energy of the first four segments(1 segment,5 segment,7 segment,11 segment)after optimization is relatively balanced,and the vibration amplitude corresponding to the maximum instantaneous main frequency after optimization is much smaller than that before optimization.(5)The concept of confidence level is introduced.The confidence level is 95%.Based on the prediction model of vibration velocity,a set of safety assessment and control model of blasting vibration is established.According to the blasting safety regulations(GB6722-2014),the safety control standard of civil houses and communication signal towers is 2.5cm/s.Based on the stress wave theory,considering the vibration speed regulation of newly poured concrete(GB6722-2014)according to blasting safety regulations,the allowable vibration speed of Nanhuan Expressway is 8.0cm/s.Based on the established safety assessment and control model of blasting vibration,the safety construction scheme suggestions for the section through the stone slab town pump station,the section through the communication signal tower and the section under the South Ring Expressway are given.Vibration monitoring on site shows that the vibration speed is controlled within the set safety control standard.