47. GENERAL. River outlets having a capacity of 15,000 cubic feet per second with the reservoir at elevation 3490, which is the minimum water surface for power operation, were installed in the dam near the left abutment. The river outlets provide for releases for downstream commitments when the powerplant is not in operation and during the period of final closure of the diversion tunnels. The outlets will also be used to maximum capacity during maximum flood releases. The centerline of the intake is at elevation 3374 which is about 30 feet above the estimated 100-year silt level in the reservoir. The outlet works consists of four 96-inch-diameter steel pipes with cast iron bellmouth intakes, hollow-jet valves for regulation, and ring-follower gates for emergency closure. A bulkhead gate, which operates under balanced head, is provided at the upstream face of the dam to provide access for servicing the ring-follower gates. A reinforced concrete trashrack structure with structural steel bars protects the entrance. The location of the outlet works is shown on figures 109 and 110. To avoid excessive velocities in the outlet pipes, a criterion was established limiting the maximum discharge of each outlet pipe to 3,750 cubic feet per second except in cases of emergency. Discharge curves are shown on figure 111. best 48. SELECTION OF LOCATION. The arrangement for the outlets in the dam was found to be two parallel outlets in each of two 60-foot-wide blocks. The centerline distance between the outlets in the dam, 15 feet 7 inches, was dictated by the required clearance for the bulkhead gate frame metalwork around the bellmouth intake. The minimum distance between the centerlines of the outlets and the radial contraction joints in the dam was set at 1-1/2 outlet diameters. Radii of bends are 4 diameters except where lack of space required using a bend of 3 diameters. The ring-follower gates are located in a chamber (fig. 112) in the dam 60 feet downstream from the face of the dam. To facilitate installation of the gates, blockouts were provided in the gate chamber floor. A vertical shaft from the chamber to the roadway at the top of the dam was provided for removing gate parts for servicing. Special expansion joints in vaults, to allow for movement in three directions, were designed for the outlet pipes where they leave the dam. These joints accommodate the movements of the dam when the dam is fully loaded (fig. 113). Since the powerplant structure occupies the entire bottom of the canyon from abutment to abutment, it was necessary to locate the outlets in the mass concrete beneath the service bay and machine shop as they leave the dam. In this area, they were set two above each other at minimum spacing. Beyond the machine shop the outlets were encased in concrete and located below the powerplant parking area. The hollow-jet regulating valves are located about 700 feet downstream from the axis of the dam. In this area, the outlet pipes are spread apart and are all brought to elevation 3175. The layout of the downstream end of the river outlets is shown on figure 114. The location of the valves and their operation were studied in a hydraulic model.1 49. STRUCTURAL DESIGN. (a) General. --The design of the river outlets was based on concrete having a compressive strength of 3,000 pounds per square inch at 28 days for structural concrete and 2,500 pounds per square inch at 28 days for mass concrete. The allowable working stresses are shown on figure 71, except that the allowable stress in the reinforcement around the pipes in the dam was increased to 25,000 pounds per square inch. (b) Trashrack Structures.-The concrete trashrack structures (fig. 115) were designed for a differential waterload of 20 feet, temperature effects, and dead load. (c) Outlet Pipes.-The reinforcement requirements around the outlets and in the surrounding mass concrete were as follows (fig. 110): (1) Bellmouth casting at intake. It was assumed that the casting could take no tensile stress; therefore the opening was reinforced for the total tensile forces due to dam stresses, internal bursting pressure, and temperature effects. (2) From the downstream end of the bellmouth intake to the upstream edge of the ring-follower gate blockout and from the "Hydraulic Model Studies of the Spillways and Outlet Works-Glen Canyon Dam." Hydraulic Laboratory Report No. 469, Bureau of Reclamation, February 18, 1964 (unpublished). £ 3179 00: Outlet No 2-- PI NO.6 "PI NO ? PI No 2 163 62 Machine shop and service bay E: 3179 00 PI No. 6. -El 3175.00 El 3168 50 PI NO 2 PI. No 5: -18.00" 472 44 Contraction joint 10: 58 P! NO 3 -2" Expansion joint Expansion joint -270 68' Contraction joints PROFILE-OUTLET NO. 3 El 3266 82~ -9610 outlet. "pipe -Mochine shop and service bay. PI No.3. Outlet No 3 -P! No 4 EI, 3179.00. -Outlet No 4 -PL NO. 6 Outlet No. 3 EI, 3175 00 94 80 2°Expansion joint E. 3168 50Expansion joint Contraction joints PI. No. ·280 44 18.00 14.56' PROFILE-OUTLET NO. 2 RIVER OUTLETS-EXPANSION JOINT VAULT COVER SLABS-PLAN AND SECTIONS........................... RIVER OUTLETS-OUTLET PIPES PLAN AND PROFILES-NOI AND NO. 2. RIVER OUTLETS-96" RING FOLLOWER GATE CONTROLS INSTALLATION RIVER OUTLETS- CONTROLS FOR 96 HOLLOW JET VALVE-INSTALLATION LIST OF DRAWINGS El. 3179.00 PI, No. 4 235.80 PI. No. 5 -62.83PI. NO. 6 * 41.04 K-18.00 -£1,3175.00 Figure 110.-Profile of river outlets. PROFILE-OUTLET NO. 4 2-18-56 ADDED CONTRACTION JOINT AND REVISED EXPANSION JOINT DRAWN DENVER, COLORADO, SHEET & OF |