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  Effect of Free Surface on Ground Vibration and Burden for Blasting Excavation

  Urban rock excavation requires low vibration and rapid excavation. The existing free surface of the blasting excavation affects the level of vibration and the excavation efficiency. In this study, an in-situ experimental test was performed to verify the free surface effects. A continuous free surface was generated with different burden using abrasive waterjet cutting technology. The blasting process was conducted after generating a deep free surface along the projected excavation line (i.e., the tunnel perimeter). Blasting-induced ground-vibration was measured using geophones and the vibration results were compared with those from a conventional blasting method. In addition, overbreak and under-break levels were measured and analyzed in order to optimize the burden under a free surface condition. This alternative blasting method with an artificial free surface can provide minimal blasting vibration and maximal burden. These conditions allow reduction of the number of holes drilled for explosive charges and the total weight of explosives needed.

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