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• <br />March 2000 <br />APPENDIX D <br />-12- <br />5.1 Remedlation of Isolated Shafts, Stopes, And Shallow Surface Mines <br />993-2099.150 <br />Based on observations made in the Phase IV area, none of the shafts appear to be more <br />than approximately 12 feet square in plan dimensions (many are S feet or less), although <br />some are very deep. The general approach to remediate isolated shafts and shallow surface <br />mines are as follows: <br />? For open excavations where the depth to bedrock is less than 7 feet to <br />the final Soil Liner Fill subgrade surface: Backfill open shafts with <br />Coarse Shaft Backfill to approximately 10 feet below the finished surface <br />grade and then place concrete, cemented rockftll, and Structural Fill as <br />discussed below. <br />0 <br />? For open excavation where the depth to bedrock is greater than 7 feet to <br />the final Soil Liner Fill subgrade surface: Backfill the open shafts with <br />Coarse Shaft Backfill to 3 feet below the soil/bedrock interface. Then <br />place concrete, cemented rockfill, and Structural Fill as discussed below. <br />? For collapsed excavations where the depth to bedrock is less than 7 feet <br />to the final Soil Liner Fill subgrade surface: Excavate collapsed <br />materials from shafts to a depth of 25 feet below finished grade, then <br />backfill with Coarse Shaft Backfill to approximately 10 feet below the <br />finished grade, and then place concrete, cemented rockfill, and <br />Structural Fill as discussed below. <br />? For collapsed excavations where the depth to bedrock is greater than <br />7 feet to the final Soil Liner Fill subgrade surface: Excavate collapsed <br />materials from shafts to a depth of 25 feet below finished grade, then <br />backfill with Coarse Shaft Backfill to approximately 3 feet below the <br />soil/bedrock interface, and then place concrete, cemented rockfill, and <br />Structural Fill as discussed below. <br />? Excavate shallow surface mines to rock or to 25 feet below the final Soil <br />Liner Fill subgrade surface. The shallow surface mines will then be <br />backfilled with compacted Select Structural Fill and/or Structural Fill to <br />the final subgrade elevation. <br />40 <br />1:19WC09RMAL REPORT%MAPPD.DW Golder Associates