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Figure 21. --Canal outlet works--Gate chambers and stilling well details.
(Sheet 2 of 2.) From drawing 328-D-951

Sump pump discharge

-Sta. 7+68.00

(3) Embankment dry (optimum moisture content); conduit filled with water and reservoir water surface at elevation 2785.0.

(4) No lateral loads on outside of conduit; a full hydrostatic pressure for reservoir water surface at elevation 2785.0 applied on inside.

The loading conditions that resulted in the most critical stresses were used in the design of concrete and reinforcement. The moments, thrusts, and shears were computed with Beggs Deformeter coefficients and checked graphically. A shell thickness of 21 inches was determined by the requirement for shear, so that no stirrups would be necessary for circumferential reinforcement.

28. Emergency Gate Chamber. The emergency gate chamber is a dome-shaped structure with its centerline at station 4+80.00. (See sec. 25 and fig. 21.) In the design of the emergency gate chamber, vertical and lateral loads were considered. The vertical load was assumed to be uniformly distributed on a horizontal projection of the gate chamber dome and equal to the weight of the embankment material above the top of the dome. The lateral loads were assumed to have a trapezoidal distribution and be equal to one-third of the vertical load intensity at any elevation considered.

The encasement for the high-pressure gate frames was designed for stresses produced by a hydrostatic head corresponding to a reservoir water surface at elevation 2785.0. This hydrostatic head was also used for determining stresses for reinforcement design. The dome was assumed fixed to the mass concrete encasing the high-pressure gate frames, and the stresses used for determining the concrete thickness and reinforcement bar sizes were computed for an assumed loading condition by conventional methods for statically indeterminate structures.

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29. Horseshoe Conduit.

The 8-foot 2-inch horseshoe conduit mentioned in section 25 extends from station 4+90 to station 7+27.58, or from the emergency gate chamber to the control house. This conduit accommodates a walkway, a 56-inch-diameter steel pipe, and a ventilating duct.

(a) Loadings. - In the design of the conduit no internal loads were considered and the embankment was assumed to be saturated to the phreatic line for normal reservoir water surface elevation 2752.0. In addition, the following loading conditions were considered:

(1) Vertical loads distributed uniformly at top and bottom of conduit; trapezoidal distribution for lateral loads on both sides of conduit.

(2) Vertical loads distributed uniformly at top of conduit and at the bottom of a triangular distribution ranging from twice the load intensity assumed for the top at each edge to zero at the vertical centerline of conduit; a trapezoidal distribution for lateral loads on both sides of conduit.

(3) Vertical loads distributed uniformly at top and bottom of conduit; no lateral loads on conduit.

(b) Design Considerations.-- The vertical loads at top and bottom of the conduit were considered equal to the weight of the embankment above the elevation of the centerline of the conduit. Stresses produced by the various loading conditions were used in the design of the concrete reinforcement. Moments, thrusts, and shears were computed and checked by the method indicated in section 27.

X30. Outlet Pipe. - The 56-inch-diameter outlet pipe, located inside the horseshoe conduit, extends from the emergency gate chamber to the control house, a distance of approximately 244 feet. The upstream and downstream ends of the pipe are bolted to metal transitions near the gates. Plate-steel supports, spaced about 36 feet apart and welded to the steel pipe, provide support for the pipe above the invert of the conduit. The supports rest on base plates attached to concrete piers which have been constructed in the bottom of the conduit. Provision was made in the design of the supports to permit axial movement of the pipe caused by temperature changes. An expansion joint, located about halfway between the upstream and downstream ends of the pipe, compensates for changes in the length of pipe resulting from temperature change. Manholes located near the upstream and downstream ends of the pipe provide access to the interior.

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The pipe was designed in accordance with the 1943 edition of API-ASME code for the 'Design, Construction, Inspection and Repair of Unfired Pressure Vessels for Petroleum Liquids and Gases. At maximum reservoir water surface elevation 2785, the maximum head at the axis of the pipe is 113 feet. The minimum shell thickness required to provide sufficient rigidity for handling and transportation was the determining factor in the selection of the pipe shell thickness, as this thickness was greater than that necessary to resist design load stresses. A thickness of one-fourth inch was selected for the pipe shell and one-half inch for the inner sleeve of the expansion joint The pipe was fabricated from low-carbon steel plates in lengths ranging from about 15 to 36 feet. Each section of shop-fabricated pipe, including the expansion joints, was given a hydrostatic pressure test at 100 pounds per square inch. The interior surface of the pipe was coated with coal-tar enamel, and the exterior surface was painted with coal-tar paint. This work was done in the field under specifications No. 3047

31. Control House and Stilling Well. - The control house and stilling well were constructed monolithically. The combined structure is located at the downstream end of the 8-foot 2-inch diameter horseshoe conduit. The control house is rectangular shaped in plan and contains a chamber for a 4- by 4-foot high-pressure gate. Provision is made for access to the 56-inch outlet pipe from this structure. The stilling well is an octagonal, vertical shaft with the bottom at elevation 2666.75, an inside distance of 16 feet between parallel sides, and a discharge lip elevation of 2700.00 For distribution of flow, dentates are provided in the inside of the stilling well on the side opposite the gate opening. A view of the control house and stilling well is shown in figure 22. A trapezoidal outlet channel with a 16-foot bottom width, 1-1/2 to 1 side slopes, and protected by riprap for the first 65 feet downstream from the stilling well is provided for the canal discharge.

(a) Design Considerations. -- In the design, the walls of the gate chamber were considered as fixed at the stilling well shaft. The walls were designed for moments produced by floor and roof loadings. The stilling well floor was assumed to be loaded with

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base pressures computed for the stability analysis. The stilling well shaft was considered as being subjected to a horizontal saturated-earth-fill load and a thrust at the walls of the gate chamber. The fill behind the stilling well wing walls was considered saturated to the top of the walls, elevation 2709.0. A saturated fill and a horizontal equivalent fluid load was considered acting at the heel of the wall. The toe and front face of the wall was considered unloaded. The walls of the gate chamber from elevation 2678.92 to elevation 2708.17 were considered loaded with horizontal earth pressure equal to one-half of the vertical load for the elevation considered. For settlement conditions in fill or structure, a horizontal load equal to three-fourths of the vertical load was investigated.

For design of the control house roof and floors at elevations 2695. 67 and 2708. 17, the following loadings were used:

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The gate frame and conduit liner encasement were designed for a hydrostatic head for a maximum reservoir water surface elevation of 2785.0.

32. High-Pressure Gates. Two 4- by 4-foot high-pressure gates are installed in the canal outlet works, one in an emergency gate chamber and the other in a regulating gate chamber in the gate control house. The gate in the emergency gate chamber is for emergency use only and is provided with a semiautomatic gate hanger for holding the gate in the wide open position. The gate in the control house is for regulating the flow of water through the outlet works and is provided with a hydraulic gate hanger for holding the gate at any required opening. Gate installations are shown on figure 23. With the gates 100 percent open, the reservoir water surface at elevation 2720.0, and the canal water surface at elevation 2705, the canal outlet works has a capacity of 300 second-feet.

Air inlet connections, connected to vent pipes, are provided on the downstream frames of both gates. There are two flanged bypass openings on the left side of the horizontal centerline of both upstream and downstream frames of the emergency gate. An 8-inch pipe with control valve provides a connection between these openings and is used for filling the outlet conduit when the emergency gate is closed and prior to opening of the emergency gate.

Each gate is operated by a hydraulic cylinder hoist, having a capacity of 85,000 pounds with the oil pressure in the oil cylinder at 750 pounds per square inch. The design of these canal outlet gates and hoists is the same as discussed for the river outlet gates and hoists in section 24.

33. Miscellaneous Equipment. Two identical pump units are provided for lifting water from a sump, located at the downstream end of the conduit and under the control gate chamber, and discharge it through piping into the outlet canal. The sump collects seepage and/or drain water from the conduit, the stilling well and control gate chamber floor. Each pump unit consists of a vertical-shaft, turbine-type pump, directly connected to a vertical-shaft, 5-horsepower electric motor. Each pump is designed for a discharge of 200 gallons per minute against a pumping head of 46 feet. The pumps are supported from the floor of the control house at elevation 2708.17 and discharge water at elevation 2706.0 into the outlet canal. The discharge piping is provided with check valves which prevent backflow through the piping from tailwater in the canal and also prevent backflow through one pump while the other pump is running. A

The control for each motor permits either manual or automatic operation through a float-controlled switch and alternator arrangement. Under automatic control, one pump starts and stops at sump water elevations 2667.0 and 2665.0, respectively, and the other pump starts and stops at sump water elevations 2668.5 and 2666.0, respectively. By means of the alternator the pump starting sequence is transposed at the beginning of each successive pumping cycle.

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