Dynamic response analysis of caverns in opencast-underground combined mining

The dynamic response of underground caverns under open blasting loads was simulated with FLAC^3D software.On the basis of data from seismic waves measured with an IDTS3850 tester,blasting vibration parameters in the case of the maximal charge amount of explosives and the shortest blasting distance were calculated with Sadowsky's empirical formula.By conversion of the velocity-time history into the stress-time history and by use of the Fish function built-in FLAC^3D software,dynamic loading was carried out by inputting the dynamic load-time history at boundary nodes or internal nodes.After comparison between the dynamic simulation and static analysis of plastic zones,displacement and stress,the corresponding impact of dynamic loads on the stability of caverns was assessed.It is shown that blasting vibrations can magnify the vertical displacement of caverns,especially in intersect zones,and on the other hand,the stress concentration under static action is alleviated when a dynamic load is applied.Besides,it also aggravates the wall fall of cavities,but cannot result in overall destruction.