Generator sole plate supports were designed for the synchronous out-of-phase torque which was 16 times normal torque. In addition, these soleplates were located so that they spanned across passageways below. Anchor bolts for the soleplates were shortened so that they would not project into lower placements. The use of shortened bolts was approved by the generator manufacturer.

Specifications allowed the contractor the option of using prepacked or conventional concrete in the second-stage construction. Although the prepacked option had been included in Bureau specifications for some time, Trinity and Clear Creek Powerplants were the first Bureau structures in which it was utilized by a contractor.

A discussion on prepacked concrete is contained in section 104.

Conventional design procedures and allowable strengths were used in the design since prepacked concrete was considered a construction technique.

203. Superstructure. (a) Superstructure Structural Steel. --The design of the superstructure structural steel for both Trinity and Clear Creek Powerplants is contained in subsection 105(a).

(b) Reinforced Grouted Masonry Walls. --Details of the reinforced grouted masonry walls are shown on figure 168. The walls consist of an inner and outer masonry facing with grout filling the void between. The thickness of the wall, size and type of masonry units and high-lift or low-lift construction were options permitted in the specifications. These options were permitted in order to obtain the most favorable bid.

The high-lift option allowed the contractor to construct masonry facing a maximum of 12 feet in height before placing the grout in the void between. The maximum allowable lift of grout was 3 feet in the high-lift option and one brick tier in the low-lift option. Short time intervals were required between lifts. A minimum of 4 inches clearance between masonry facings was required in the high-lift option and 2 inches minimum in the low-lift option.

The transformer deck along the b-line was raised to the top of the concrete parapet to facilitate handling of the transformers from trucks. The resulting joint between the wall and concrete deck was a possible point of water seepage from the deck into the powerplant. A curb, which was made integral with the wall, was provided to prevent this seepage and subsequent damage to the interior finish. Electrical conduits were permitted to run in any direction in the grout between facings and resulted in a neater overall appearance from that of exposed conduit.

Reinforced grouted masonry walls were selected for the plant due to its location in an area of seismic activity, which indicated the need of a structural wall. Accordingly, they were designed to withstand all applicable loads as shown on figure 165. Analysis was similar to that employed for reinforced concrete with proper adjustments for the type of construction and materials employed.

It was assumed that the walls spanned in the vertical direction only. Horizontal masonry wall reinforcement was designed only for temperature stresses and to tie the structure together. Metal anchor straps on 16-inch horizontal centers were placed at approximately 12-foot vertical centers to decrease the vertical span. These straps were designed as both tension and compression members. A horizontal beam was assumed in the masonry wall at their line of embedment. A steel beam was placed between main columns to support the straps.

Horizontal masonry wall reinforcement was specified as 3/16-inch deformed side bars with 1-1/8inch-diameter deep welded crossties at right angles to the side bars. Drips were not allowed in the crossties since they had to withstand the hydrostatic load due to grouting the center portion of the wall. The steel had a yield stress of 80,000 pounds per square inch and the design was based on the high-lift method. The design was not revised for the low-lift method selected by the contractor.

(c) Takeoff Structure. --The design of the transformer takeoff structure for both Trinity and Clear Creek Powerplants is contained in subsection 105(c).

204. Powerplant Afterbay Control Structure and Channel. The elevation of Clear Creek Powerplant is such that control of the tailwater is a requirement when the water surface in Whiskeytown Reservoir is below certain levels. The tailwater is controlled at these times by the afterbay control structure shown on figure 169. The elevation of the weir crest of the control structure is 1186.00. This crest will develop a tailwater elevation of about 1190 for a discharge of 1,900 second-feet from the plant when Whiskeytown Reservoir water level is low enough to avoid submerging the flow over the weir.

The retaining walls of the afterbay are designed to carry the differential loading which will result from a sudden decrease in flow from the plant. The conditions for this loading are considered most critical when the full load of the plant is lost with the weir controlling the tailwater depth.

Poor quality of rock in the afterbay area required paving the floor with a concrete slab. A portion of the slab is anchored to the foundation with bolts and all of the slab is provided with weepholes.

The channel downstream from the afterbay control structure, as shown on figure 169, is a significant feature only if Clear Creek Powerplant is operated at a time when the water level in Whiskeytown Reservoir is low. It is possible that detritus and trash may be carried into the tailrace channel by flows from Clear Creek. Where these deposits occur to the extent that discharge from the plant is affected, it may prove desirable to clean them out of the channel.

"6-6" Longe 3'0" cra

See Section 8.B

SECTION H-H

DETAIL
(For Trinity only)

NOTES

@ 16" crs. vertically. (Locate directly above existing

masonry anchor slet in concrete base wall)

TYPICAL ANCHORAGE
FOR FUTURE PARTITIONS

Figure 168. --Trinity and Clear Creek Powerplants--Detail of reinforced grouted masonry walls.

Figure 169. --Clear Creek Powerplant afterbay and tail race channel--Plan, profile, and sections.

2. Building Facilities

205. Sanitary System. (a) Sewage Ejector.--A single pneumatic sewage ejector is provided in the powerhouse for handling sewage to the septic tank. It is rated at 30 gallons per minute when operating at a total discharge head of 30 feet. It consists of one 30-gallon receiver tank complete with necessary operating valves, electrodes and controls. Provision is made for installing a second ejector if found necessary.

(b) Septic Tank. --The tank is located above grade on the north wall of the powerhouse. It is designed for a flow of 500 gallons per day with a 36-hour retention period. Effluent is discharged into an absorption trench located at the edge of the service area.

206. Access Area Drainage Plan. The access area drainage plan for both Trinity and Clear Creek Powerplants is discussed in section 107.

3. Major Hydraulic Equipment

207. Hydraulic Turbines. (a) Description and Operating Requirements.--The turbine installation for the powerplant consists of two vertical-shaft Francis-type, 225-r. p. m. hydraulic turbines with shop-welded plate steel spiral cases in five sections having welded-on cast-steel flanges for assembling in the field. The elbow-type draft tubes have welded plate steel liners down to the pier noses. Each turbine has a capacity of 99,000-horsepower at full gate and best efficiency head of 535 feet. At this best efficiency head and when developing 93,500-horsepower, the manufacturer's warranted efficiency of the turbine is 90.2 percent.

The effective head on the turbines will usually vary between 500 and 670 feet, with an expected average head of 535 feet. The controlling design water surface elevations, in feet, are as follows:

The estimated head loss from forebay to each unit is approximately 136 feet with a total discharge through the units of 3, 200 second-feet. At the manufacturer's rated head of 514 feet and full gate output, the predicted discharge from each turbine is 1, 740 second-feet.

(b) Turbine Design. --The turbines were furnished by Hitachi New York, Ltd., of New York City, N. Y., in accordance with the requirements of invitation No. DS-5277. The turbines were designed and built by Hitachi, Ltd., of Tokyo, Japan. Their operating characteristics and design information are summarized on the hydraulic turbine data sheet, figure 170. Figure 171 shows a sectional assembly view of the turbine. Material specifications of the stress-carrying parts and the maximum unit stresses allowed in the design are as given in section VIII of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code. The turbine spiral case was designed for an internal hydrostatic pressure of 465 pounds per square inch which is the maximum expected operating pressure including water hammer. It was tested in the shop and again in the field with a hydrostatic pressure of 700 pounds per square inch. A pressure of 230 pounds per square inch was maintained within the casting while the concrete surrounding it was placed.

Each turbine is designed and constructed so that all removable parts can be removed from above through the circular opening beneath the generator and through the bore of the stator. Provision was made in the design to permit the rotor, runner and main shaft as a whole to be jacked up one-fourth inch for removal or adjustment of the generator thrust bearing. The turbine shaft and runner may be lowered fiveeighths inch from their normal position to clear the generator shaft when the coupling bolts are removed. When so disconnected, the runner with the turbine shaft will rest on a ledge in the discharge ring provided for this purpose. The runner is designed to support only its own weight and the weight of the turbine shaft when in this position.

The turbine runner is of welded construction with 18-8 cast stainless steel buckets and cast carbon steel crown and band, made in one piece. It has a maximum diameter at the top and bottom of 11 feet 55/64 inches and a discharge diameter of 8 feet 1-45/64 inches. It is designed and constructed to safely withstand the stresses due to a speed of 433 revolutions per minute, which is the runaway speed under an effective head of 670 feet. The design clearance of the upper and lower runner seals is 0. 049 inch.

The turbine shaft is made of forged steel and is designed to operate at full runaway speed without vibration or objectionable distortion. A 6-inch-diameter hole is bored axially through the shaft for visual inspection. The upper end of the hole is permanently plugged. The turbine shaft is polished where it