OceanaGold Waihi North Project Vibration Performance Assessment Page 27 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 Water Sprays Although a review of the literature has not returned any information on the success of fine mist water sprays as a technique for controlling overpressure from tunnel blasting, there is some evidence to suggest that it has been successfully used in European civil applications. It may be possible to model the effects of water sprays using very high humidity levels with environmental noise models. Developing the Favona decline showed that elevated levels of overpressure could occur during the initial stages of establishing the decline. Any blasting associated with developing the portals and initial stages of the WUG access decline will involve monitoring the level of overpressure. Mitigation measures like those used at Favona will also be trialled. The geometry of the tunnel with the bend approximately 100 metres from the portal is expected to be the most effective method of limiting elevated overpressure values for the remainder of the tunnel blasting. 14. MITIGATION MEASURES The analyses have reasonably guaranteed that the levels of vibration and overpressure from the blasting will comply with the proposed criterion at potentially sensitive locations. If the analyses have underestimated the level of vibration as a result of the geology differing from that which has been used in the calculations to develop the relationship between vibration level, distance and explosive quantity, or other unknown factors lead to increased levels of vibration, several mitigation procedures are available and could include: Limiting the quantity of explosive by further reducing the length of the blasthole; Using multiple explosive decks per blasthole, each separated by a column of inert material, to reduce the quantity of explosive contributing to the peak vibration level; Incorporating an air deck above the explosive column to reduce the overall quantity of explosive loaded into the blasthole, but maintain the same blasthole length; Adjustments to the mine design to limit the length of the explosive column initiated at single nominal time; Adjustments to the method of mining, such as using cut and fill or other smaller scale methods; Reducing the blasthole diameter; Adjustments to the initiation sequence; and Alternative explosive types, including both low density products and cartridge explosives. Similar types of adjustments have on occasions been previously implemented as part of the mining process at Waihi. Variations in the ground type have often necessitated changes to the blasting approach. Importantly, the mine design has shown flexibility and adaptability to account for these changes. There are no aspects of the WNP designs that suggest similar mitigation measures could not be implemented should they be necessary to reduce vibration impacts to ensure compliance with the proposed vibration criteria. 15. VIBRATION MONITORING The method for assessing the impact of vibration from the blasting for the project will differ according whether the blasting is for the GOP and the access drive between the processing plant, or for the WUG blasting. In both scenarios, the monitoring and analyses of the data will remain largely consistent with the approach that OceanaGold has implemented for the Correnso, REX, Martha and other orebodies at Waihi. 15.1. Access Tunnel Vibration Monitoring The monitoring equipment for demonstrating vibration compliance for the GOP and access tunnel will remain unchanged from current practices which have been shown to be appropriate. Vibration monitoring systems capable of reporting the vibration level from each of three orthogonally arranged sensors together with the instantaneous vector sum value will continue to be used to record the
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