Infrasound induced by blasting in a limestone mine propagates to the houses in a neighboring village and vibrates their windows, doors, furniture and so on. This infrasound causing vibration becomes an apparent problem for the limestone mine near a village. The most effective way to reduce the vibration is to reduce the blasting scale, but this cannot be performed because of low efficiency for mining. Another effective way is to shift and reduce the dominant frequency of infrasound by changing the delay time of blasting caps so that it may not overlap the resonance frequencies of vibrated objects, but the necessary conditions to do so have not been shown. In this paper, in order to propose the necessary conditions for setting an optimal delay time of blasting caps to reduce the vibration, the infrasound of many patterns of blasting was measured in the face of Ube-Isa Limestone Mine and at a neighboring house of the mine. At the neighboring house, the windows vibration was also measured. From the analyses of these measured data, it was found that the longer delay time of blasting caps is necessary to reduce the lower frequency component causing a large vibration, and shorter one is necessary to shorten the duration of blasting and reduce the resonant vibration. Then, in order to satisfy these conflicting conditions, a varied delay time of blasting caps was proposed and tested. As a result, the windows vibration was reduced 60% in total energy and 24% in maximum displacement compare to the minimum vibration of usual blasting using a fixed delay time of blasting caps.
