Agenda - 10-14-1993 - D 1 - Laserfiche WebLink

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and RJ 8507 are the current standards for defining methods of monitoring ground motion and air blast respectively. The U.S. Bureau of Mines has developed standards for ground motion caused by blasting events. These standards were developed as a result of extensive testing and analysis of various blasting conditions and are calculated so that damage to properly built structures will not occur if sucn standards are met. According to U.S. Bureau of Mines, Bulletin 656, blasting limit of 2.0 inches per second peak particle velocity is a safe level of ground movement for structures. The Nortri Carolina Division of Mines has adopted regulations reducing this ground motion limit to 1 inches per second. Martin Marietta has set an internal company limit for ground motion of inches per second. A history of seismograph recordings at the American Stone site show trat Martin Marietta has never exceeded this .50 inch per second limit, An independent analysis for ground vibration performed in October 1992 measured two locaticrs within the American Stone Company property during two separate blast events. At the vicfn,*i of the quarry main office (approximately 1800 ft. from the blast) the maximum estimated magnitude of ground velocity was 0.1 in./sec. At the rim of the pit (approximately 925 ft. away from the blast), the maximum estimated magnitude of ground velocity was 0.2 in./sec. The damage threshold (the magnitude of ground vibration at which damage can be expected) is in./sec., and therefore typical blast events at the quarry are not likely to cause any structura/ damage to nearby residential property. North Carolina Division of Mines guidelines for air blast limits are set at 128 dBL. A history blast waves monitoring indicates that American Stone Company has never exceeded this limit the quarry property. American Stone Company maintains files with respect to blast activities ar monitoring. These records are available for inspection. 3-28