Trinity River Division Features of the Central Valley Project, California: Design

Soils properties were selected from Laboratory Report No. EM-590.3/ Sample No. 33R-1 was considered to be representative of available impervious material and had the following properties:

For zone 2, a unit wet weight of 106 pounds per cubic foot was assumed along with a friction factor of 0.7 and cohesion equal to 0.

The least factor of safety of 1.7 occurred during the drawdown state. Zone 1 embankment was considered to be relatively incompressible, and the drawdown flow net sketched according to the Casagrande4/ method. Pore water pressures were estimated from this flow net. If an earthquake of sufficient intensity to generate an outward horizontal force of 0.05 gravity and a vertically downward force of the same magnitude were to act on the dam during drawdown, this factor of safety should decrease only slightly. Earthquake forces cited are those used on Trinity Dam. 5/ Since the embankment is founded on relatively sound rock, sliding through or along the foundation material was not believed possible under the designed stresses.

(f) Surface Settlement Points. --Surface settlement points will provide information on cumulative settlement and deflection of the surface of the dam with respect to the crest centerline. Settlement points are located on the surface of the completed embankment on four lines parallel to the crest centerline at the following approximate distances: 21 feet upstream, 19 feet downstream, 95 feet downstream, and 439 feet downstream.

306. Spillway. For spillway plan, sections, and details, see figures 239 through 243. The spillway consists of an approach channel, an uncontrolled crest at elevation 795.0, an open chute, a stilling basin, and an outlet channel. The discharge curve is shown on figure 239. The capacity of the spillway with the reservoir at maximum water surface elevation 809. 5 is 5, 260 second-feet.

307. Outlet Works. The outlet works, as shown on figure 244, consists of the following:

(1) An unusual intake structure which extends up the face of the dam to provide for raising the intake sill as sediment fills the reservoir. Sections of trashracks will be shifted to higher elevations and replaced by precast cover sections. Details for placing these sections are given on figure 245.

(2) A 6-foot-diameter circular conduit, a gate chamber with tandem high-pressure gates, an access shaft with elevator, a shaft house enclosing gate controls, a free-flow 6-foot 6-inch diameter flat-bottom conduit, a stilling basin, and an outlet channel.

The outlet works has a capacity of 710 second-feet with the reservoir water surface at maximum elevation 809. 5.

308. High-Pressure Gates and Motor-Operated Lifts. Four 2-foot 3-inch by 2-foot 3-inch stainless steel high-pressure gates are installed in the gate chamber of the outlet works. The two downstream gates are used to regulate the flow of water through the outlet works. The two upstream gates are used for emergency closure to permit inspection and repair of the two regulating gates. The gates will operate under a maximum head of 170.37 feet and are operated by electric-motor-driven gate lifts. The lifts were manufactured by the Philadelphia Gear Co. of Philadelphia, Pa. Each lift is designed to raise the gate at a rate of 6 inches per minute. See figure 246 for the gate installation.

Each motor is controlled by two local pushbuttons, one marked "Raise" and one marked "Lower." The lifts are equipped with limit switches to stop the gate at upper and lower extremes of gate travel. In addition, the regulating gates may be operated by supervisory control from Keswick Powerplant. Each lift has a position indicator to show the amount of gate opening, and a rotating stub shaft extending through the gearcase which is connected to a digital telemeter storage unit for transmitting the gate position to Keswick Powerplant.

309. Electric Elevator. A freight elevator is installed in the access shaft as a means of transportation for workmen, materials, and equipment between the control house and the gate chamber. The travel of the car is 171 feet 1-13/16 inches from the top landing in the control house at elevation 818.00 to the bottom landing in the gate chamber at elevation 646.85. There are no intermediate landings between these elevations. The elevator platform is 3 feet 4 inches wide by 2 feet 2 inches deep, and the car has a maximum

3/Snively, R. C., "Laboratory Tests on Proposed Embankment Materials, Spring Creek Debris Dam, Trinity River Division, Central Valley Project, California, " Earth Materials Report No. EM-590, Bureau of Reclamation, August 31, 1960 (unpublished).

4/Casagrande, A., "Seepage Through Dams, " Contributions to Soil Mechanics 1925-1940, Boston Society of Civil Engineers, p. 295.

5/Memorandum: "Seismic Resistance--Trinity Dam--Central Valley Project, California, " to F. C. Walker from E. E. Esmiol, Bureau of Reclamation, February 13, 1957 (unpublished).