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~S ~ <br />~ 1 ~V nU <br />Southwestero Portla¢d Ceme¢t <br />Mi¢i¢g Impacts o¢ Mo¢tgomery School <br />SHB AGRA Project E93-7038 <br />Page 4 <br />' The study by King and Algermissen (1985) is the referenced source for establishing the 0.079 <br />inJsec allowable vibration criteria used in the U.S. Geological Survey sponsored studies of <br />' archeological ruins and historic adobe structures. This ground vibration compliance limit was <br />established based on the summary of the literature, with no dynamic analysis of the actual <br />stresses and strains induced ground vibrations for comparison with the structure's tolerance. In <br />' a subsequent report (King et al., 1991), it was noted that "The general vibration standazd is set <br />for structures that can be repaired without loss of historical significance. Because of the <br />irreplacebility of the (subject) structures, the historic contents and the absence of knowledge of <br />~' the cumulative effects of low to medium level vibrations on adobe construction, a conservative <br />level of 2 mm/sec (0.079 in/sec) was established at Hovenweep, Chaco Canyon and Mesa Verde <br />National Pazks". The 0.079 in/sec vibration value is essentially an acknowledged conservative <br />value selected from the literature with consideration to the fragile nature and historic value of <br />the structures to which it has been applied. <br />4.0 RECOMMENDED LIMITS FOR BLAST RELATED EFFECTS <br />The most restrictive ground vibration compliance values found in the literature is the 0.079 <br />in/sec level recommended by the U.S. Geological Survey for fragile stone masonry azcheological <br />ruins. This compliance level was established without a valid technical basis, but was rather an <br />' acknowledged lower bound level that provides a high degree of safety for fragile and unique <br />structures. Considering the nature of the construction of the Montgomery School Building and <br />the current and previous uses of the building, it does not appear that the 0.079 in/sec vibration <br />' limit is applicable. As previously discussed, monitoring by Siskind et.al. (1980) has established <br />that normal occupancy of a building results in maximum vibration levels of over 1.0 in/sec and <br />levels frequently exceeding 0.5 in/sec. <br />' Based on this, it is overly conservative to restrict an occupied structure such as the Montgomery <br />School to allowable blasting related vibrations of 0.079 in/sec while normal occupancy can result <br />' in vibrations in excess of 1.0 in/sec. A more realistically conservative limiting ground vibration <br />can be established that limits the blast induced building vibration to levels comparable to those <br />which the building is subjected to due to current and historic occupant activity. Using a limiting <br />' value of 0.5 in/sec for vibration in the structure and conservatively assuming the building can <br />amplify the ground motion by a factor of two, a 0.5 inJsec vibration in the building would be <br />induced by a 0.25 in/sec ground vibration. Accordingly, a limiting blast-induced ground velocity <br />' of 0.25 inlsec would be a realistically conservative compliance value to apply to a historical <br />structure such as the Montgomery School relative to blasting induced ground vibrations. This <br />ground vibration level would limit structural vibrations to the levels that would be comparable <br />' to vibration associated with normal occupancy. <br />As previously noted, the controlling requirement for limitation of air over pressure is the <br />' potential for glass breakage which would be independent of the historic construction of the <br />Montgomery School Building. Compliance with air over pressure limits as discussed in the <br />' Blasting Vibrations Analysis report (SHB AGRA, 1993b) must be meet at the nearest structure <br />L, A G R A <br />' Eerth & Environments/Group <br />