Study On Dynamic Response Law And Control Measures Of Filled Subgrade Under Blasting Load

In recent years,with the rapid development of China’s economy and the acceleration of urbanization,infrastructure construction has also been rapidly developing.In order to solve the problem of urban surface traffic congestion,the development and utilization of underground space have developed rapidly.When tunnels pass through fill areas and are constructed using blasting methods,if reasonable blasting control measures are not taken,it may cause safety accidents such as fill roadbed collapse and tunnel arch collapse,Due to the significant loss of life and property,it is of great significance to study the impact and control measures of underground tunnel blasting construction on the filled roadbed.Based on the research background of a subway tunnel project under a fill subgrade in Chongqing,this thesis studies the dynamic response law and control measures of the fill subgrade under blasting load by referring to relevant domestic and foreign literature and supporting engineering data,combining theoretical analysis and numerical simulation methods.The main research results are as follows:(1)Based on Hypermesh&Ls dyna finite element analysis software,a three-dimensional numerical model was established for calculation and analysis,revealing the propagation law of seismic waves in the form of wavefront spreading and attenuation along the filled subgrade,and finally tending to disorder,and the velocity response of the surface and slope was studied.The results show that the peak vibration velocity of surface particles occurs at the projection position of the arch,mainly in the vertical direction;The vibration velocity of slope particles increases with elevation,resulting in a "amplification effect".Within a certain height difference range from the slope surface,the vibration velocity of slope particles is greater than that of the slope body,which does not comply with the general law of blasting vibration attenuation.(2)Using the control single variable method,the overall peak kinetic energy of the filled soil roadbed and the peak vibration velocity of typical monitoring points were used as evaluation indicators to explore the dynamic response changes of the roadbed under different cyclic footage,filling height,and maximum single segment dosage.As the cyclic footage increases,the peak kinetic energy of the roadbed and the peak vibration velocity of the monitoring points rapidly increase;When the filling height increases,the peak kinetic energy of the roadbed is basically the same,and the peak vibration velocity of the monitoring points shows a decreasing trend,and there is a hysteresis phenomenon;Increasing the maximum single segment dosage increases the peak kinetic energy of the roadbed and the peak vibration velocity of the monitoring points,and the trend of dynamic response changes remains basically consistent;When the blasting parameters take a cyclic footage of 1m and a maximum single segment charge of 9kg,the effect of reducing the surface vibration speed of the roadbed is optimal.(3)Selecting the vertical vibration velocity at the projection position of the arch as the evaluation index,and using the optimal combination of blasting parameters,the peak particle vibration velocity is 3.16cm/s at the most unfavorable filling height,which is greater than the vibration velocity control threshold of 2cm/s.Based on the actual construction situation,it is necessary to adopt engineering control measures such as vibration reduction ditches.When the height of the vibration reduction ditch is 1.5m,the influence of the depth of the vibration reduction ditch and the filling height on the vibration reduction rate was analyzed;As the depth of the damping ditch increases,the damping rate increases;Under the action of the damping ditch,an increase in filling height will lead to a decrease in the damping rate.After comparing and analyzing different working conditions,it was finally determined that the reasonable depth of the vibration reduction ditch is 1m.At this time,the peak particle vibration velocity at the most unfavorable filling height is 1.65cm/s,which is less than the control threshold.