advance of completion of the dam or the postponement of grouting until after the completion of the dam as required to control the load conditions at the time. of grouting the contraction joints. The load distribution between the arch and cantilever elements is found by the trial-load method which has been in use by the Bureau of Reclamation engineers for several years. This method has been improved recently by the use of unit loads which have reduced the work materially. GATE INSTALLATION The gate installations in the dam include sluicegate outlets at elevation 2,370, needle valve outlets at elevation 2,470, and power penstock outlet at elevation 2,570. High water in the reservoir is at elevation 2,670 and the top of dead storage is at elevation 2,590. The sluice-gate outlet will consist of three outlet conduits, each conduit being controlled by two 4 by 5 foot cast-iron sluice gates, arranged in tandem alignment and operated by oil-pressure cylinders from a gallery in the dam. The needle-valve outlet will consist of three cast-iron lined conduits, each conduit being controlled by a 48-inch balanced needle valve and a 4 by 4 foot high-pressure emergency gate. The needle valves will be mounted at the downstream end of the conduits and the emergency gates will be located near the upstream face of dam. Operation of emergency gates will be by oil-pressure cylinders from a gallery in the dam. A 4-ton traveling crane will be installed in the valve house to serve the needle valves. The power penstock outlets will power penstock outlets will consist of two 6-foot conduits, each controlled by a 5 by 6 foot cast-iron emergency gate. The gates will be operated by oil-pressure cylinders from a gallery near the upstream face of the dam. The outlet The outlet conduits will bend downward and enter the canyon wall within the base of the dam, terminating in a common penstock tunnel at a distance of about 50 feet from the base of the dam. The penstock tunnel and power plant are not to be constructed at the present time. TRASH-RACK STRUCTURES All of the different outlets from the dam are protected by trash-rack structures of the same general design. These consist of a reinforced concrete semicylindrical structure, carrying rack bars of structural steel. The bars are 6 by 8 inch steel bars spaced 6 inches on centers in the sluice-gate and needle-valve outlet and 6 by 1⁄2 inch steel bars spaced 34 inches on centers in the power penstock structure. The rack velocities in sluice-gate outlet will vary from 2.1 feet per second under a 50-foot head to 5.3 feet per second under a 300-foot head. In the needle-valve outlet the rack velocities will vary from 0.9 foot per second under a 25-foot head to 2.6 feet per second under a 200-foot head. The rack velocities for the power outlet will be less than 1 foot per second. DIVERSION TUNNEL The designs provide for a 22-foot diameter horseshoe tunnel 1,005 feet long, for diversion of the river during construction, the greater part of the tunnel being utilized for the permanent spillway. The tunnel intake is designed with provision for temporary closure utilizing headwall grooves, and keyways are provided upstream from the spillway shaft for final closure by means of a concrete plug. Studies of the capacity curve of the diversion tunnel as compared with the maximum river discharge of record indicate a height of cofferdam of about 60 to 75 feet. SPILLWAY The spillway will consist of a vertical shaft connecting with the diversion tunnel at a point 240 feet below the tunnel intake. The spillway shaft will be controlled by a 60 by 12 foot spillway ring gate operating in an annular pressure chamber formed in the spillway crest structure. The ring gate is a floating type crest similar in operation to the drum gate but designed with much better hydraulic conditions for flow into a vertical spillway shaft. The gate will be of structural-steel construction embodying 12 shop-riveted segments, which are riveted together in the field to form the complete ring gate. The operation of the ring gate will be controlled automatically by a needle-type valve in the same manner as the recent drum-gate installations of the Bureau of Reclamation. The application of the ring gate for spillway control is believed to be new, and the engineers who developed this device are making application for patents on the gate and some of the control features. This type of gate effected a material saving in cost as compared with the usual drum-gate installations. Concrete in needle-valve house, trash-rack struc tures, etc.. Placing reinforcing steel, ..cubic yards.. ...pounds__ Installing pipe and fittings for grouting radial con traction joints.... Installing and painting gates and purtenant metal work.......... 825 675,000 are being made with the Idaho Power Co. to transmit power generated at the Government power plant at Black Canyon Dam over the company lines as far as ---pounds__ the Ontario-Nyssa substation and from this point the 115, 000 valves with apGovernment is constructing a 66,000-volt single-circuit ---pounds. 1, 760, 000 wood-pole transmission line to the dam site. A 2,000kilovolt-ampere step-down substation will be provided at the dam site and power will be sold to the contractor at 2,300 volts at rates to be stated in the contract. Installing and painting structural steel ring gate with appurtenant metal work. ---pounds.. Installing and painting trash-rack steel_____do____ CONSTRUCTION RAILROAD 440, 000 A railroad for transporting construction materials to the dam site is already under construction, having been contracted to the General Construction Co., of Seattle, Wash., for completion November 21, 1928. This railroad will run from its junction with the Homedale branch of the Oregon Short Line Railroad near Dunaway Siding, Oreg., to the dam site, a distance of about 24 miles. The railroad will be of standard gauge with 70-pound rails, having a maximum grade of 0.5 per cent toward the dam and 1 per cent from the dam. ELECTRIC POWER FOR CONSTRUCTION Electric power for construction purposes will be available at the dam site at 2,300 volts. Arrangements SAND AND GRAVEL PITS Excellent sand, gravel, and cobbles are available for the construction of the dam from natural deposits in the vicinity of Dunaway Siding, Oreg. The construction railroad connects with the Homedale branch of the Oregon Short Line Railroad at this point. The gravel pits are owned by the Government and no charge will be made to the contractor for the materials used in the construction of the dam. Preliminary tests indicate that practically all of the materials in the pit, with the possible exception of a small percentage of sand, can be utilized in the concrete and that the material will make durable concrete of high strength. Cobbles up to 8 inches in diameter will be utilized in the concrete. HIGH-PRESSURE RESERVOIR OUTLETS By C. M. Day, Mechanical Engineer, Denver Office, Bureau of Reclamation A COMPREHENSIVE record of the development of design, installation, and operation of highpressure reservoir outlets in dams constructed by the Bureau of Reclamation prior to the year 1921 is contained in a report issued in 1923, entitled "HighPressure Reservoir Outlets," by J. M. Gaylord, electrical engineer, and J. L. Savage, designing engineer. This report contains a brief historical sketch of ancient control works; typical designs of gates and of arrangement and design of outlet works; design data for gates, valves, and hoists; and a record of the design, installation, and operation of gates, hoists, valves, conduits, and other features in the principal dams constructed by the Bureau of Reclamation up to that date. There have been no radical changes in the design of high head outlets since the publication of the outlet report, the principal developments being in minor improvements in design of outlet works as a whole to avoid troubles previously experienced in operation, and in detail designs of gates and valves to improve their operation and reduce their cost. This chapter will be devoted to a description of the later designs and no attempt will be made to review the history of high-pressure outlets as contained in the report by Messrs. Gaylord and Savage. A high-pressure outlet is considered by the Bureau of Reclamation as one in which water is discharged from a reservoir under heads greater than 75 feet. Below this head the ordinary type of slide gate may be used for regulation of discharge, provided air vents in back of the gate are provided and assuming the gate is properly designed. For heads greater than 75 feet experience has shown that slide gates do not give satisfactory service, even though provided with air vents, as the unbalanced hydraulic conditions cause vibration and cavitation, and the gate deteriorates rapidly. For these reasons, for heads above 75 feet slide gates are in the main used only where the gate is operated fully open, for sluicing purposes or as emergency gates for protection of regulating valves below. HIGH-PRESSURE GATES A gradual process of evolution, commencing with the first installations, has occurred in the design, construction, and installation of these gates, and as experience and use have developed inherent weak nesses, improvements have been made that removed the undesirable features, improved operation, simplified design, and reduced the cost. This reduction in cost has resulted from a study of the stresses induced under installation and operation which has permitted rearranging and proportioning the parts so as better to distribute the forces and disseminate the stresses, thus reducing the amount of metal required. Consideration is constantly given to modern foundry and shop practice and the designs are so prepared that shrinkage strains are eliminated as much as possible in castings and unusually difficult machine operations are avoided. A typical design for a high-pressure slide gate is given in the accompanying illustration which shows a 5 by 5 foot emergency gate in the Gibson Dam on the Sun River project, Montana. The principal parts of such a gate are the upstream and downstream frames, forming the water passage for a distance below the gate leaf, bonnet, bonnet cover, and hoist cylinder. The upstream and downstream frames are recessed and fitted with bronze strips serving as seats on which the leaf moves. Similar bronze strips are provided on the face of the gate leaf, but of a different composition, the two compositions having been developed from experiments to determine the most suitable bronzes for carrying extremely high moving loads without abrasion. Tests showed that the two bronze compositions used by the Bureau of Reclamation, designated Class "C" and Class "D" bronzes, would successfully carry a load of 3,000 pounds per square inch, but for design purposes the maximum loading used is 500 pounds per square inch. The gate frames and bonnet are not designed to withstand the internal pressures to which they may be subjected. They are of rugged construction and heavily ribbed, to avoid strains and distortion in the foundry, but the internal pressures are taken by the concrete in which the gates are embedded, suitably reinforced for the maximum pressure to which the gate may be subjected. The bonnet cover is designed. to withstand full reservoir head of water on the under side, plus the stresses that may be induced when a pressure of 1,000 pounds per square inch is applied in the hoist cylinder for closing the gate. The hoist cylinders are designed for a working pressure of 1,000 pounds per square inch. They are bronze lined, and a system of weep holes in the cylinder, connected with a system of ducts between the lining and cylinder, is provided to eliminate possibility of oil leaking past the piston on the outside of the lining, thus destroying the lining. The gate stems are made of a high grade of rolled bronze having an ultimate tensile strength in excess of 100,000 pounds per square inch, thus avoiding requirement for a brass sheathing on a steel stem. crete and rock. All gates are now provided with air vents, the size depending on the service for which the gates are to be used. For instance, for a 5 by 5-foot gate used for emergency purposes only, an 8-inch air vent pipe, branching into two 6-inch connections at the gate, is used. Forgates used for sluicing purposes, which might be left open for a considerable period, a larger High pressure gates for Gibson Dam, Sun River project, Montana, undergoing shop tests vent pipe would be used. All emergency gates are provided with a bypass pipe for filling the conduit below the gate, thus permitting normal operation under balanced pressures. Emergency gates, however, are designed for closure under unbalanced pressures due to full reservoir head. Hydraulic operation of the gates is by means of a triplex pump capable of delivering from 1,000 to 1,200 pounds pressure, the capacity varying from 7 to 12 gallons per minute depending on the size of the hoist cylinder and the desired time for gate closure. A cheap grade of light lubricating oil is used as an operating medium. For control of gate operation a high-grade straightway plug type of valve has been found most satisfactory. The control-pipe system is of the open type, provided with an air chamber and relief valve. For outlet works of the type at McKay Dam on the Umatilla project in Oregon, where it is undesirable to place the pressure pump and motor, or engine, as the case may be, in the gate chamber, what is termed an "automatic gate hanger" has been developed by which the gates can be operated from the valve house at the tunnel outlet. This automatic gate hanger is mounted on top of the hoist cylinder, and has a locking device that supports the weight of the gate leaf, stem, and piston. This locking device is controlled by the oil A first-class commercial grade of graphited flax packing used in the hoist cylinder, which passes through suitis used in the stuffing boxes. In earlier installations, as at Pathfinder Dam, described in Chapter IX of the outlet report, no provision was made for air vents immediately below the gates. This resulted in the formation of a vacuum which gradually ate away the metal in the conduits, and in cases where the gates discharged into a tunnel and the tunnel below became sealed, the breaking of this vacuum had the effect of an explosion, destroying metal linings and tearing out large quantities of con7939-297 able ports into a cylinder in the gate hanger, thence to the top or bottom of the hoist cylinder, to raise or lower the gate, as desired. The cylinder, piston, and ports in the automatic gate hanger are so designed that the locking device must function before the pressure is applied in the hoist cylinder, thus preventing damage to the locking device. Provision is also made for a system of signal lights that indicate the raised and lowered position of the gate, and also show when the locking device functions. |