| With the rapid development of transportation infrastructure in China,the number of highway tunnels in mountain areas is also increasing.The application of small spacing tunnel in highway tunnel is increasing gradually because of the flexible wiring outside the hole,which can better adapt to the terrain conditions in the mountainous area.At present,the construction of the mountain tunnel is still mainly based on the drilling and blasting method.However,when the small spacing tunnel is in the drilling and blasting construction,due to the small clearance between two adjacent tunnels,the vibration effect of the following tunnel in the blasting excavation will inevitably affect the safety of the adjacent former tunnel structure,and the vibration effect is more prominent for the tunnel with poor surrounding rock geological conditions.Therefore,in order to reduce the risk of tunnel construction,it is of great practical significance and value to study the dynamic response and control measures of adjacent former tunnel under the action of blasting vibration.In this paper,taking Yunlongshan small spacing two-line tunnel in Beijing as the research background,the blasting vibration monitoring and numerical simulation are used to study the vibration effect of following tunnel blasting construction on adjacent former tunnel and its vibration control measures.The main research work is as follows:(1)Combined with the on-site blasting construction,the blasting vibration waveform diagram and data obtained from the monitoring were analyzed and processed,and the attenuation law of the axial vibration velocity of the former tunnel in front of the following tunnel blasting palm are obtained.At the same time,the dominant frequency of blasting vibration is analyzed,and the dominant frequency distribution and attenuation law of the vibration signal are obtained.(2)Based on the principle of wave packet analysis,the optimal wave base "sym8" is selected.The time-frequency characteristics of blasting vibration signals measured in adjacent tunnel are analyzed by using wavelet packet transform method.The reconstructed waveforms and spectrum of vibration signals in different frequency bands are obtained.At the same time,the energy distribution characteristics of vibration signals are studied.(3)The three-dimensional model corresponding to the actual project is established by using the finite element software LS-DYNA.The peak vibration velocity of the particle in the adjacent tunnel is obtained by calculation,and compared with the measured vibration velocity,which verifies that the numerical simulation method is feasible.On this basis,the influence of blasting on the vibration of the adjacent former tunnel lining under different surrounding rock grade is studied,and the variation law of axial vibration speed,stress and displacement of the former tunnel and the vibration response of the lining after the excavation of the lower step are further analyzed.(4)Through numerical simulation method,the cutting hole charge is divided into multiple sections according to different proportions for millisecond blasting.The effect of blasting vibration of different millisecond time intervals in the case of two-section and threesection cutting on the adjacent former tunnel is studied.The optimal millisecond time interval is obtained by comparing and analyzing the peak vibration velocity of particles with different time intervals.At the same time,the influence of arranging the vibration damping ditch with different parameters on the vibration damping effect is discussed.According to the calculation results,the blasting plan of the following tunnel is optimized specifically for the cut hole,and a series of vibration reduction treatment methods are proposed to provide guarantee for safe construction. |
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