Study Of Vibration Testing And Numerical Simulation On Metro Tunnel Excavation Blasting

With the rapid development of urban transportation industry, a large number of subways will be constructed, and part of the subway tunnels need to be excavated by drilling and blasting due to the restriction of engineering geological conditions. But the subway tunnels are mostly located in the centre of city, in which the ground surface buildings are numerous and the environment is complicated. The vibration effects produced by blasting may endanger the safety of ground surface buildings, which make the blasting construction more difficult. As a result, it is very important both in scientific significance and application value for studying the propagation characteristics and attenuation laws of blasting seismic wave on the ground.In this paper, based on the safety monitoring of Guang-Hu section tunnel excavation blasting in WuHan metro line 2 project, lots of the monitoring data are obtained through the real-time monitoring during excavation blasting, which established the practical base for the paper. The collected vibration data are analyzed and combined with the calculation of numerical simulation software. The main contents and conclusions are as follows:(1) The regression analysis is used to analyze the surface vibrating velocity in front and back of the tunnel face by the least square method, and the parameter values k and a in the empirical formula which is fit for the area are determined. There is a good correlation when the surface vibrating velocity along the tunneling direction is fitted by Sadaovsk formular, and it can be forecasted by the formula, whereas the fitting correlation is poor in the opposite direction and the formula is not suited to forecast the blasting vibration intensity. The primary frequency of blasting seismic wave is analyzed by the statistical method. It is found that the primary frequency is mainly concentrated between 10-60Hz, which is far greater than the natural frequency of the building, basically the resonance phenomenon will not be occurred.(2) Contrasting the surface vibrating velocity in front and back of the tunnel face, it is found that the surface vibrating velocity in back of the tunnel face which has been excavated is larger than that in front, therefore, the amplification effect of surface vibrating velocity in the tunnel must be taken into account when the choice of blasting scheme will be determined, otherwise it is likely to endanger the safety of ground surface buildings which is in back of the tunnel face.(3) When the charge weight per delay interval is constant, the experiment results demonstrate that the peak partical velocity of blasting seismic wave is exponentially augmented with the increase of scale distance.of explosive under even ground, but gradually diminished with the increase of explosive distance, the attenuation of the blasting seismic wave is faster when it is near the explosion source, while that will be slower when it is far from the explosion source, and there is an amplified phenomenon. The primary frequency is appeared randomly and decreased with the increase of propagation distance on the whole.(4) The formula of charge weight per delay interval in the process of tunnel excavation blasting is put forward, also the relationship between explosive distance and charge weight per delay interval is fitted under the condition of different allowable peak partical velocity.(5) The cut-hole blasting of tunnel excavation blasting is simulated by dynamical finite element program ANSYS/LS-DYNA, and the propagation laws of tunnel excavation blasting are gained, but the vibrating velocity in numerical simulation is larger than that in practical monitoring, and the waveform is relatively simpler. The studies are carried out on the characteristics of surface vibration and the attenuation law of vibration wave. It shows that the results of numerical simulation agree well with the spot experimental monitoring results. It is proved that the established simulation method is effective when it is used to predict and analyze the vibration of engineering blasting.