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An initial estimate of a safe level criterion is possible from the <br />particle velocity strain comparisons frvm figures 6 and 8, and extrapolating <br />particle velocities corresponding to 150 to 239 /lin/in from table 5, the <br />strains corresponding to 18 pct of minimum yield strength. Minimum peak <br />particle corresponding to class B, x42 and x56 pipelines are then 5, 6 and <br />8 in/s, respectively, for vertical vibrations and sliyhtly higher for radial. <br />It is important to consider if this approach is conservative. The <br />18 pct criteria allowed for traffic still includes a safety factor, the <br />Specified Minimum Yield Strength (St1YS) itself tras a safety factor in that it <br />is a "minimum", and the blast data are well contained by the maximum value <br />envelopes. Strains ar•e calculated as worst-case biaxial. Furthermore, the <br />low frequency (and potentially higher strain-producing vibration) found Ire re <br />(5.6 liz) is about as low as could be expected for such close-in blastiny <br />(ref. 9). On the other hand, the pipeline may not yet be fully coupled after <br />only 6 months in ttre ground. The soil over tfre pipelines was softer than <br />nearby undisturbed ground even after six months. <br />Blasting Criteria for PVC Pipeline <br />Unlike the steel pipeline, the specified maximum pressure produces far <br />less hoop stress than 72 pct of St1YS (table 5). !t is likely that there is <br />some other limiting factor, such as the couplings. The strain corresponding <br />to the maximum operating pressure of 160 lb/inZ is 4800 Itin/in, contrasting <br />strongly with tire yield failure strain of 17,500 frin/in. Again, a rough <br />estimate of particle velocity is possible from the strain figures and a <br />duubling for circumferential strain, wiriclr was not monitored on the PVC. (ln <br />retrospect, it would have been better to forgo some longitudinal gages for. <br />additional circumferential ones). Assumirry a strain equal to 5 pct of that <br />produced by pressurization, or 1.35 pct that of yield, and tfre worst case <br />maximum strain envelope (from fig. 7), the corresponding peak particle <br />velocity would be about 10 in/s. Because of the lack of actual <br />circumferential strains this level should be further reduced urrlil more data <br />are available. Possibly, users of PVC pipe have an environmental criterion <br />similar to the 18 pct SMYS suggested for steel. <br />CONCLUSIONS <br />This paper describes a study of full-scale blasting near pressurization <br />pipelines and contains an preliminary analysis of results. The authors expect <br />provide an additional comprehensive report (BuMines Rl, likely) with all <br />measurements, additional analyses, and comparisons with other analytical <br />studies and predictions. In the interim, it is suggested tfrat 5 in/s be <br />permitted far large surface mine blasts at Class B or better steel pipelines. <br />Also those of Class 6 or better PVC. It is suggested that this criterion not <br />be applied at construction sites iF experience Iras shown that higher particle <br />velocities are tolerable. Also, in the interim, rrv adjustnierrt is needed for <br />pipeline age assuming the protective coating is intact and unless the pipeline <br />is known to be at higher risk from previous damage or other cause. <br /> <br />13G <br />