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<br />March 2000 <br />APPENDIX D <br />-15- <br />993-2099.150 <br />? Backfill the shaft with Coarse Shaft Backfill to an elevation <br />approximately 10 ft below the final Soil Liner Fill subgrade surface in <br />areas with a soil thickness of 7 feet or less. If the soil thickness exceeds <br />7 feet, backfill the shaft with Coarse Shaft Backfill to 3 feet below the <br />soil/rock interface. <br />? Compact final layer of Coarse Shaft Backfill. <br />? Remove weak weathered rock and surficial soils at the collar to form a <br />cone with minimum side slopes of 0.511:1 V. <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 />Any shafts identified on Drawing Nos. 1 and 2 that cannot be located on the surface will <br />• be remediated by placing geogrid over an area sufficiently large to account for inaccuracies <br />in precisely locating the portals on surface (approximately 50 feet x 50 feet). The geogrid <br />will be designed to span across potentially opening sizes of 10 to 12 feet at the entrance to <br />the tunnel. <br />The proposed approach for remediation of shallow shafts and pits is as follows: <br />? Excavate feature down to rock or 25 feet below the final Soil Liner Fill <br />subgrade surface. <br />? Backfill with compacted Select Structural Fill and/or Structural Fill to <br />final Soil Liner Fill subgrade surface. <br />C1 <br />1AM099WWAL REPOR7UMAPPD.DOC <br />Golder Associates