EGL Ref: 8983 23 June 2022 Page 15 WAI-985-000-REP-LC-0004_Rev0.docx This report shall only be read in its entirety. The tailings at Waihi typically consolidate to a low permeability soil. Laboratory permeability tests undertaken in 2010 and 2017 indicate values from 7 x 10-11 to 6 x 10-9 m/s. However, higher values are indicated through consolidation modelling of the settlement measured in Storage 2. It indicates typical tailings permeabilities in the range from 1 x 10-9 to 1 x 10-7 m/s. 10.0 DESIGN BASIS 10.1. Dam Design Criteria Guidelines for the design, construction and operation of dams have been produced by the New Zealand Society on Large Dams (NZSOLD), a technical group of Engineering New Zealand. The guidelines are referred to as the New Zealand Dam Safety Guidelines (NZDSG Ref.4). The latest version of the guidelines was published in 2015. It represents current best practice and adherence with the guidelines has become mandatory by Building Consent Authorities, Regional Councils and Territorial Authorities. The NZDSG has a dam classification system that reflects the consequences of failure and includes engineering design advice appropriate to the hazard posed by the dam. A dam’s classification is termed its Potential Impact Classification (PIC). There are three classes (Low, Medium and High). A High PIC classification has been used in developing the design standards and criteria for the new TSF. Details of the adopted design criteria are summarised in Table 1. Table 1: SUMMARY OF PROPOSED DAM DESIGN CRITERIA Design Parameter Design Criteria Flood (In Flow Design Flood) Runoff from PMP (72 hour) rainfall event Earthquake • OBE Probabilistic 150 year return period • SEE 84th percentile level for the CME developed by a deterministic approach and need not exceed the 1 in 10,000 AEP ground motions developed by a probabilistic approach. Aftershock of one magnitude less than the SEE within one day. • Aftershock 1 in 10,000 AEP ground motions developed by a probabilistic approach. Aftershock of one magnitude less than the SEE within one day. Stability • Static • Seismic -End of construction Factor of Safety (FOS)≥1.3 -Long term operational steady state FOS≥1.5 -Long term post closure steady state FOS≥1.5 - Rapid drawdown FOS≥1.3 - Post-earthquake conditions FOS 1.2 OBE: The performance requirement for the OBE is
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