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Koehler Tunnel Bulkhead <br />Certification Report <br />Page 2 <br />Bulkhead Buffer -Lime Placement <br />One ton of hydrated lime was placed between the cofferdam and upstream face of the <br />Bulkhead. <br />Bulkhead location preparation (scaling and washing) <br />The bulkhead site was scaled clean of loose material and sandblasted to remove any <br />surface coating that may have been present. It was then washed down and vacuumed <br />clean of water, sand and rock residue. This stage of site preparation was adequate to <br />maximize the potential for bonding between the rock and the concrete bulkhead and was <br />also inspected by the design engineer, John F. Abel, Jr., and DMG during their respective <br />pre-pour inspections. <br />Removal of fractured rock resulted in a height that exceeded the original design <br />assumption. In order to check the validity of the design, John Abel Jr., the design <br />engineer, was asked to check the design using actual dimensions. His report, attached, <br />verified that the original design with #10 rebar on 14 inch centers on the downstream side <br />and #6 rebar at 12" centers for the upstream side. <br />BV-pass or diversion pipe <br />The diversion pipe through the bulkhead is a 4" Schedule 40 -stainless steel pipe fitted <br />with one thrust collar (3/8" thick - 2" larger in diameter than the pipe) and two light <br />gauge seep collars. The thrust collar was placed at a distance of greater than 5' from the <br />downstream face to allow any loads to be distributed to the tunnel walls. Two seep collars <br />were placed, upstream and downstream of the thrust collar, to minimize the ability of <br />impounded water to travel along the outside of the pipe. The pipe entrance was extended <br />upstream to a temporary cofferdam, placed to keep the bulkhead area dry during <br />construction. The pipe system was adequate to keep the area dry until after the concrete <br />had sufficient time to cure. <br />The outlet end of the by-pass pipe was equipped with a stainless steel gate valve and <br />blind flange. At the owners stipulation, the pipe was not grouted closed in order to <br />accommodate drain-down of the mine pool at a future date in the event the owner desires <br />to re-open the Koehler Tunnel. <br />