Micro-meter crack response to rock blast vibrations, wind gusts & weather effects

Micro-meter dynamic crack responses in a two story structure to rock blasting- and wind gust-excitation are compared to those induced by long term climatological effects. These measurements substantiate the conservancy of the 12.5 mm/s (0.5 in./s) blasting vibration control to protect residential structures against cracking. The test structure was instrumented with both velocity transducers to measure superstructure motions as well as special micro-meter displacement sensors to measure crack expansion and contraction. Crack responses to 48 to 64 km/hr (30-40 mph) wind gusts were equal to those generated by blasting vibrations of 11.5 mm/s (0.45 in./s) or 90% of the control limit. There are few reports of wind responses in the rock blasting literature because the long period of the wind "drift" motions produces low structural velocity responses, which are below the noise (and thus trigger levels) of most standard seismographs. The paper closes with an assessment of the frequency of occurrence of significant wind gusts during an average weather year.