Study On Vibration Velocity Analysis And Vibration Reduction Measures Of Primary Support Structure Of Tunnel Under Blasting Condition

In the process of tunnel excavation by drilling and blasting,the impact and damage of blasting on surrounding rock mass and structures has been a widespread concern of relevant researchers.It is difficult to accurately predict the impact of blasting due to the randomness and complexity of blasting stress wave.Taking Yunlongshan Tunnel in Beijing as the background,based on the field measured data,combined with the regression method,continuous wavelet transform and numerical simulation method,the vibration velocity attenuation law of tunnel blasting is obtained,the information contained in the vibration velocity curve is found,and the optimal setting value of vibration damping parameters is proposed.Firstly,the blasting vibration velocity curve measured on site is de noised by wavelet denoising,and the peak value of vibration velocity is extracted;the attenuation law of peak value velocity is obtained by regression analysis.With the help of dimensional analysis method,the traditional Sadowski formula is modified,and the modified parameters are introduced as follows: free surface area,minimum resistance line and hole depth and diameter.The vibration velocity attenuation formula in line with the full face multi-stage blasting is obtained.Then,the non-stationary signal of blasting vibration is analyzed and deconstructed by continuous wavelet transform.It is found that the chromatogram obtained by continuous wavelet transform can reflect the energy distribution of blasting vibration,and the optimal scale can also reflect the frequency of blasting vibration velocity curve.With the help of the wavelet coefficients under the optimal scale,the blasting vibration velocity curve can be divided in the time domain,and different wavelet bases can correspond to different curve characteristics,so we can further study the non-stationary signal in mathematics.Finally,the measured curves before and after vibration reduction of three vibration reduction methods(vibration reduction hole method,staggered phase interference method and compound cut method)are compared and analyzed.It is concluded that the vibration reduction hole method has the best effect among the three vibration reduction methods.With the help of numerical simulation method,the influence of setting parameters of three kinds of vibration reduction measures on the vibration reduction effect is studied.It is concluded that increasing the depth of damping holes,decreasing the spacing of damping holes and increasing the number of rows of damping holes will enhance the damping effect.The conservative value of the depth of damping holes is 3.5m,and the vibration velocity attenuation rate is 17.9%.The spacing of holes and the number of rows of damping holes can be determined according to the actual needs of the site.The best time interval is 2.5ms and the vibration velocity attenuation rate is 22.1%.The results show that the vibration reduction effect is the best when the distance of shallow cut hole is 3.6m,and the vibration velocity attenuation rate is 20.8%.The above research results provide a reference for the vibration velocity test and attenuation law research of similar projects,and have a positive guiding significance for the implementation of related vibration reduction schemes.