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• <br />?J <br /> <br />APPENDIX D <br />March 2000 -13- 993-2099.150 <br />Any laterals off of the shafts will be remediated as identified in Section 5.2. These <br />recommendations are based on Golder's experience in underground mining applications <br />and the experienced gained during the Phase III remediation program. The Structural Fill, <br />which is supported by the concrete and cemented rockfill, is designed to form the VLF <br />Foundation. The concrete and cemented rockfll plugs are designed so that the plugs are in <br />compression and develop frictional resistance along the sides of the excavated opening. <br />For the shafts that are proposed to be backfilled in the upper portion with concrete and <br />cemented rockfill, the upper layer of Coarse Shaft Backfill will be compacted using a <br />method specification. A three feet layer of construction grade concrete will then be placed <br />on top of the compacted Coarse Shaft Backfill. The role of the concrete is to form a <br />competent base to the cemented rockfill plug above the backfill. The design requirements <br />for the concrete are that if the backfill beneath the concrete settles or is dislodged in any <br />way, the cemented rockfill will not unravel. The cemented rockfill plug above the <br />concrete will be inverted cone shaped, and even if the backfill settles, the vertical loads <br />from the VLF will largely be transmitted through the cemented rockfill and into the <br />surficial soils and bedrock. The walls of the shaft will be naturally sufficiently rough that <br />the concrete layer will not move under gravity loading if the backfill settles. <br />While the cemented rockfill is capable of spanning across the shaft opening (or even larger <br />openings) without any concrete layer beneath, it is proposed that cement be added to the <br />rockfill above the concrete layer as a conservative redundancy in the event the concrete <br />layer moves for some unexpected reason. It is routine practice in many underground <br />mines to completely undercut cemented rockfill of this nature over exposed spans of <br />20 feet or more without experiencing any instabilities of the fill. The concrete layer <br />provides added security that unraveling of the cemented rockfill cannot occur. <br />More detailed descriptions of the proposed remediation of the shafts and shallow surface <br />pits are presented below. <br />1:%991I09MNAL REPORT1 MA"D.DW Golder Associates