Historically, Project Owners and Regulators have used very conservative criteria when blasting in the vicinity of dams and hydropower structures typically reverting to "residential level" peak particle velocity (PPV) limits based implicitly on work by the US Bureau of Mines that was concluded in the late 1980's. Unusually restrictive acceleration criteria may also be set for electronic and electrical components using spectra that are well above the range typically measured when blasting. These criteria significantly restrict the potential for blasting to be effectively used and typically steer Contractors towards mechanical breakers and other less productive, more expensive rock breakage methods. This paper will examine, explore and detail approaches to demonstrating how close-in blasting can be "engineered" to meet Owner's objectives. It will also examine blast monitoring and geotechnical instrumentation systems that can be used to demonstrate that the Owner's structural performance objectives are met. Case studies will be presented where higher than typically allowable PPVs have been permitted and a case where limits were not raised but blasting was successfully performed, albeit at a higher cost. Recorded PPV data on structures of concern are included and compared against scaled distance and predicted PPVs. Ultimately, this paper will demonstrate that when proper planning, blasting design criteria, and review are incorporated into a comprehensive specification and blasting program around critical structures, higher PPV criteria can be established for more economical and effective project construction. The Authors hope that this paper will be of help to Owners planning for and/or engaged in rock excavation near critical structures.
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