Effects of Axial Air Deck on Blast-Induced Ground Vibration.

The technique of air-deck charge has been applied in open-pit blasting for a long time. However, the effects of axial air deck in borehole on blast-induced ground vibrations have not been well investigated. In this study, the influences of axial air deck on blast-induced peak particle velocities (PPVs) are investigated based on field tests and numerical simulations. Five blasting tests with the ratios of top axial air deck (i.e., defined as the air-deck volume in borehole divided by the borehole volume) of 0/16, 1/16, 2/16, 3/16 and 4/16 are implemented in an open-pit mine. PPVs and their attenuation trends corresponding to different air-deck ratios are analyzed and discussed. The test results show increasing air-deck ratios can decrease near-field ground vibrations to some extent. In addition, numerical models with single borehole are built and validated with blasting test results. The influences of air-deck positions, air-deck ratios and air-deck numbers in single borehole on near-field ground PPVs are investigated with the calibrated numerical models. It is found that near-field ground PPVs induced by the top air-deck charge are lower than those induced by the bottom and middle air-deck charges when the air-deck ratio is the same. Meanwhile, the variation of air-deck ratios located at the top of borehole has a greater influence on near-field ground PPVs than that located at the middle and bottom of borehole. With the increase of the number of air-deck layers in one borehole, near-field ground PPVs induced by the top air-deck charge increase, while those induced by the middle and bottom air-deck charges decrease. [ABSTRACT FROM AUTHOR]