Figure 8. Blast mats were lifted and positioned by a crane. Vibration Considerations Vibration concerns had to be factored into the blast design. There was a 100-year-old railroad bridge 170 ft (52 m) downstream parallel to the existing bridge. Calculations to predict the vibration intensity at the bridge told us that we could expect minimum levels of disturbance from the planned explosive loads at that location. However, the prime contractor who was working under time constraints, continued with building the supports for the new bridge. The plans called for 6 1/2 ft (2 m) diameter reinforced concrete shafts drilled about 20 ft (6.1 m) into the sandstone bedrock that would serve as the foundation of the new structure. Scheduling of pier demolitions needed to be planned around the curing of the concrete in the new piers. One of the new columns was only 27 ft (8.3 m) from one of the piers to be demolished. An equation that was used to predict potential vibrations indicated that the PPV expected could be in the 7 inch (18 cm) range. Research of the appropriate literature indicated that vibration levels of more than twice that amount would not cause any damage to this type of reinforced concrete structure. After the holes were loaded and the connections secured Available in the Blasters' Library MICROMETER CRACK RESPONSE TO VIBRATION AND WEATHER BY CHARLES H. DOWDING PUBLISHED BY ISEE A Must-Read for those in the explosives industry. Anyone dealing with the effects of vibrations will value this book! Regulators Gain an appreciation of the degree of conservatism in the current control limits and explore the possible use of autonomous micrometer crack measurement to explain to the public why they are more sensitive to vibration than are structures. Litigants Explore the large effect of natural phenomena on crack response and its effect on questions of causation. Owners of Vibratory Sources Investigate the use of graphical display of crack response to educate neighbors about various natural phenomena that affect their house. Engineers Explore use of micrometer crack response to study the response of structures to natural phenomena as well as for the control of the construction process. Instrumentation Specialists Learn how to measure micrometer crack response and how to integrate the process with seismological systems and instruments. ISEE Member: $92 Non-Member: $114 Order online at www.isee.org ISEE * 30325 Bainbridge Road * Cleveland, OH 44139 * (440) 349-4400 * Fax (440) 349-3788 January/February 2015 The Journal of Explosives Engineering 13http://www.isee.org