2001-03-15_REVISION - M1977378 (3)

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Terry Tunnel Near Surface Bulkhead Construction Certification Report Page 2 Bulkhead location preparation (scaling and washing) The bulkhead site was scaled clean of loose material and sandblasted to remove any surface coating that may have been present. It was then washed down and vacuumed clean of water, sand and rock residue. This stage of site preparation was adequate to maximize the potential for bonding between the rock and the concrete bulkhead and was also inspected by the design engineer, John F. Abel, Jr., and DMG during their respective pre -pour inspections. By -pass or diversion pipe The diversion pipe through the bulkhead is a Schedule 40 steel pipe fitted with one thrust collar (3/8" thick — 2" larger in diameter than the pipe) and two light gauge seep collars. The thrust collar was placed at a distance of greater than 5' from the downstream face to allow any loads to be distributed to the tunnel walls. The seep collars were placed between the thrust collar and the upstream face to minimize the ability of impounded water to travel along the outside of the pipe. Bars were welded inside the pipe (upstream side) to provide a stop for the grout pig to simplify grouting the pipe full upon completion of the bulkhead. The pipe entrance was extended upstream to a temporary cofferdam, placed to keep the bulkhead area dry during construction. The pipe system was adequate to keep the area dry until after the concrete had sufficient time to cure. Construction of concrete forms and erection of rebar cages The forms were constructed of vertical 8 "x8" S4S posts and horizontal 2 "x12" and 2 "x6" S4S lagging. 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 water -side rebar cage is #6 bars on a 12 "x12" grid and the air side rebar cage is #10 bars on a 6 "x6" grid. The minimum clear distance from the form to the water -side rebar is 3" ( #6 bars) and the minimum clear distance for the air side is 3.5" ( #10 bars). The minimum bulkhead length was specified to be 7' and the actual length was 7'3 ". 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.