OceanaGold Waihi North Project Vibration Performance Assessment Page 24 of 41 Project Number: HP2006-2 Heilig & Partners Save Date: 21/06/2022 5:55:00 PM ABN 56 082 976 714 File Name: WAI-985-000-REP-LC-0018_Rev 0 The vibration contours for WUG show levels of vibration similar to that modelled to occur from the Golden Cross mining activities. The contours are similar to the blasting in the Golden Cross areas where dominant frog populations received levels of vibration around 8 to 10mm/s. The modelling results are provided in Appendix D. No blasting at WUG will be noticeable to occupants of properties around the area. Unlike Correnso where properties were located above the stopes, the production blasting for the WUG will occur more than 5 kilometres in plan distance from properties. When compared to previous blasting at Favona, Trio and Correnso, the explosive quantities are similar to the modelled weights for WUG. The blast designs required to achieve the necessary production rates will therefore be similar also. Given the method of mining and permissible range of explosive weights, the modelling confirms WUG can be effectively blasted and remain compliant with conditions based around the herpetologists’ recommendations for the Archeys Frog. 12. GLADSTONE OVERPRESSURE ASSESSMENT Overpressure monitoring has been completed infrequently at Waihi. The data set is therefore small and insufficient to develop a site-specific regressed relationship between the measured level, distance and explosive quantity. Other groups like the United States Bureau of Mines (USBM)5 have proposed relationships showing the expected level of overpressure as a function of distance and explosive quantity. A common reference equation for estimating the overpressure is shown below: = 163−24 × � √ 3 � The form of the overpressure relationship is consistent with the Australian Standards AS2187.2. These relationships have been used elsewhere in assessing blasting impacts and they provide an indication of the likely level, noting that it is generally accepted that overpressure prediction is more difficult than estimating vibration levels as there are multiple other factors that impact upon the maximum measured level. The location of the receiver relative to blast affects overpressure levels with those receivers in front of the blast commonly measuring 6dBL higher than those behind. Similarly, receivers downwind can measure 6dBL higher than those upwind of the same blast. Blasting from the Martha open pit has generated low and compliant levels of overpressure when monitoring has been undertaken. Given the increased separation distance between the GOP blasting and the nearest receivers, when compared to the Martha open pit blasting, and the requirement that blasting is controlled to generate minimal movement of the blasted rock, overpressure levels are expected to remain low and have been confirmed by the overpressure modelling results. Plate 1 in Appendix E shows the modelled levels of overpressure from blasting in the upper area of the GOP where the pit geometry is not as beneficial in shielding and reducing overpressure levels as would occur at the deeper areas of the pit. The overpressure relationship is consistent with that given above and estimated from other sites where controlled quarry scale blasting has been undertaken which necessarily involves larger bench heights with appreciable burden movement. The relationship is therefore expected to result in predictions that lie at the upper end of measured results. The modelling is based on an explosive weight of 16 kilograms per blasthole. When blasting at the crest of the GOP, the minimum separation distance between the blast and the properties is around 300 metres. With an explosive weight of 16 kilograms, the expected overpressure levels will be less than 115dBL. 5 Siskind, D.E., Stachura, V.J., and Stagg, M.S., 1980. “Structure Response and Damage Produced by Airblast from Surface Mining”, United States Bureau of Mines, Report of Investigations No 8485.
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