Discussion on “Impact of orientation of blast initiation on ground vibrations” [J Rock Mech Geotech Eng 15 (2022) 255–261]

Recently, Garai et al. (2022) published a paper on the impact of orientation of blast initiation on ground vibrations. However, some of the claims are not supported by the results of the given tests. In Fig. 1 (see Fig. 8 in Garai et al., 2022), there are contours of measured vibration velocities in 4 directions (every 90°) and an incorrect interpretation between them. By placing all measured vibration velocity values (Gerai et al., 2022) at well-defined points on a single figure, it was not possible to precisely determine the type of vibration velocity, such as radial, tangential and vertical vibration velocities, with their different shapes. An incorrect conclusion was also drawn about the direction of the highest vibration velocity. The paper by Garai et al. (2022) measured the vibrational velocity of the medium through which the seismic wave passed, but used the incorrect term shock wave. The shock wave would have destroyed the seismic measuring instruments. A superposition of the vibrational velocity was considered, but not combined with the vibrational frequency of the seismic wave. This paper presents a method for selecting the time delay between successively initiated explosive charges to the measured frequency of the seismic wave, so that the direction of initiation of the explosive charges does not affect the vibration velocity of the ground through which the seismic wave passes. The theoretical and measured shapes and waveforms of radial velocity and tangential velocity in an opencast lignite mine are then presented. Moreover, the conditions for the formation of shock wave, transition wave and seismic waves are presented.