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• APPENDIX D <br />March 2000 -14- 993-2099.150 <br />The proposed approach for remediation of open shafts is as follows: <br />? Backfill the shaft with Coarse Shaft Backfill (12 inch minus) to an <br />elevation approximately 10 feet below the final Soil Liner Fill subgrade <br />surface where the soil thickness is 7 feet or less. In areas with soil <br />thicknesses greater than 7 feet, the shaft is to be backfilled with Coarse <br />Shaft Backfill to 3 feet below the soil/rock interface. The 12-inch minus <br />Coarse Shaft Backfill material should be suitable to minimize the <br />bridging across the void, and minimize the amount of processing <br />required to meet the specification. <br />? Compact final layer of Coarse Shaft Backfill using a method <br />specification approved by the construction manager and engineer. <br />? Remove weak weathered rock and surficial soils at the collar to form a <br />cone with minimum side slopes of 0.5H: IV. <br />• <br />? Place 3 feet of concrete as initial backfill. <br />? Backfill with 7 feet of compacted cemented rockfill (2 inch minus Fine <br />Shaft Backfill with 6 percent cement by weight). <br />? Backfill to grade, as needed, with Structural Fill. <br />The proposed approach for remediation of currently collapsed shafts deeper than 25 feet is <br />as follows: <br />? Excavate collapsed materials in the shaft 25 feet below the final Soil <br />Liner Fill subgrade surface. <br />? Compact upper layer of native material. <br />?71 <br />1A9A2099 V4AL AlPMr2099APPD.DW Golder Ass dales