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~I(~IPJ~ ~ ~~lVIR(~NM`~,`~i ~',_ ~"E~~II~~S PLC <br />2.6 Earthquake <br />An important factor in the design of a water impoundment such as a dam or a <br />mine bulkhead is the determination of the integrity of the structure under possible <br />earthquake conditions. This calculation considers the effect of the water <br />impounded in a direct line of sight behind the bulkhead being accelerated under <br />conditions of the design basis earthquake. <br />Design basis earthquake accelerations for use in the calculations were obtained <br />in accordance with the 2003 National Earthquake Hazards Reduction Program <br />(NEHRP) Seismic Design Provisions, using the United States Geological Survey <br />Java Ground Motion Parameter Calculator, Version 5.0.8. The results of this <br />computer run are documented near the end of the Structural Calculations, under <br />Tab 3. <br />The acceleration used was 0.239 g, corresponding to the expected maximum <br />earthquake acceleration under a 0.2 second interval. <br />2.7 Concrete specifications and mix design <br />The Concrete specification is located at Tab 7. The concrete specified for the <br />project was intended to meet several constraints: <br />• Self-compacting characteristics, to eliminate the need for vibration of the <br />mass pour; <br />• Low heat of hydration; <br />• High sulfate resistance; <br />• Good pumpability. <br />Concrete mix design data is included at Tab 9. <br />The formwork specifications and shop drawings are included at Tab 8. In <br />general, the critical issue with the formwork is that it must withstand the forces of <br />the concrete (full hydrostatic head for self compacting concrete) plus the forces <br />imposed by the pump overpressure, assumed to be 50 psi at the delivery point. <br />2.8 Grouting plan and specifications <br />The MES proposal to Cotter identified two options: contact grouting only, or an <br />enhanced grouting program, intended to pressure-grout the blast-shattered, <br />jointed rock of the adit perimeter. <br />To maximize protection of the environment, Cotter elected to have MES <br />implement the more advanced grouting program alternative, to further reduce the <br />potential leakage flow around the bulkheads. <br />7 <br />