OceanaGold Waihi North Project Vibration Performance Assessment Page 5 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 Figure 5 - Plan of the WUG Development 3. EFFECTS FROM BLASTING Drilling and blasting have been used to fragment rock for all mining at Waihi over the previous 30 years. The method is highly efficient and allows the rock to be broken in manageable size fragments for excavation. Because the explosive detonates very quickly, a great quantity of energy is introduced into a relatively small volume of rock, which in turn creates a vibration pulse that propagates through the rock mass. Vibration remains the key assessable effect from blasting with other effects such as overpressure, flyrock and blast fumes identified as relevant although not necessitating the same level of assessment. As the vibrational pulse travels outward from the source, it diminishes or attenuates. With increasing distance, the affected area greatly increases, but the energy becomes widely dispersed. In general, the amplitude (size) of the vibration can be expected to decrease by approximately two-thirds for every doubling of the distance. Many factors are known to affect the way that a vibration pulse propagates from the blast. Different rock masses affect the rate at which the vibration reduces with the distance from the blast. Competent, high strength rock masses allow more efficient transmission of vibration whilst weaker and softer materials generally attenuate vibration to a greater degree and vibration levels are lower at the same distance from the blast. Other factors, such as water, faults and fractures, open voids and so on, together with the explosive properties, impact on how vibration propagates. Combined, it is not uncommon for the same blast design to generate very different levels of vibration, depending on the combination of factors present in different ground. A two-fold difference in vibration level for a similar blast design at similar distances is typical. A substantial database of vibration levels as a function of blast design and distance from the blast has been developed. In addition to vibration, other impacts from blasting include overpressure (air borne vibration) and flyrock. The potential impacts depend upon the nature of the operation (open pit or underground) as well as the scale of blasting and the proximity of the activities to sensitive receivers. Neither overpressure nor flyrock are relevant to underground operations, perhaps except for those blasting activities that may be required for the initial development of a decline near to the surface portal. Both vibration and air overpressure will occur to varying extents from the open pit blasting associated with WNP. Through appropriate blasting practices and blast design guidelines that vary the scale of
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