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Koehler Tunnel Bulkhead Certification Report Page 3 Construction of concrete forms and erection of rebar cases The forms were constructed of vertical 8"x8" S4S posts and horizontal 2"x12" and 2"x6" S4S lagging. The form interior was lined with'/4" plywood for additional strength. Bracing consisted of angle iron and pipe anchored to the ribs, sill and back of the drift. The form construction and bracing was adequate to prevent movement or failure during filling of the forms. The rebar cages were supported by dowels (rebar) grouted into the rib. The upstream rebar cage is #6 bars on a 12"x12" grid and the downstream rebar cage is #10 bars on a 14"x 14" grid. The minimum clear distance from the form to the rebar is 3.5". The minimum bulkhead length was specified to be 12' and the actual length was 12'. Trim bars (5' long) were placed at 45° to the rebar around the cutouts in the rebar cage for the pipe. All minimum clearances, dimensions and spacings met design criteria and were inspected by the design engineer prior to filling of the forms. Perimeter area irregularity The rock contact perimeter area irregularity required to develop the design compressive strength of the concrete when subject to the maximum design thrust was determined to require a projection of 0.14" or more. Quantification of a minimum perimeter area irregularity was not specifically calculated due to the blocky irregularity on the back, ribs and floor extending more than 1 ft. into the tunnel cross section. Pumpins of concrete, fillinE of forms and concrete compressive strength The following concrete mix was used for this bulkhead. The concrete mix was as follows: #/cu. vd. Portland Type V 720 Sand 1692 Fine Aggregate - 3/8" 1093 Fly Ash, Class F 115 Water 324 Delay Set The concrete was batched from the portable Sandco batch plant that was set up in Silverton. This is the same plant and concrete supplier used for the American Tunnel