Figure 277.-Installation view of outlet pipes. Partially buried in concrete, two of the outlet pipes poke their way skyward at Glen Canyon Dam. P557-420-5806, March 20, 1961.

were supplied by Goslin-Birmingham Co. under invitation No. DS-5269 and the two control cabinets were furnished by Kendo, Inc., of Denver, Colo. under invitation No. DS-5498.

The ring-follower gate is of cast and welded steel construction and consists of a body, a leaf, and a hydraulic hoist which is an integral part of the gate. The slide-type gate with a leaf includes a follower ring having a circular opening equal to the diameter of the pipe to provide an unobstructed water passage when the leaf is in the open position. The hoist cylinder is 27 inches in diameter and has a travel of 8 feet 8 inches.

The two control cabinets are of steel construction and enclose the control system for two ring-follower gates in each cabinet. The control system was installed in the gate chambers of the river outlets in the dam and was used to operate the four ring-follower gates. The opening and closing of the gates is controlled from a pushbutton station located in each cabinet. The ring-follower gates were received at Flagstaff, Ariz., beginning in May of 1961 and shipment was substantially complete by October 16, 1961. The control cabinets were received at Flagstaff on September 29, 1962.

The ring-follower gate installation was performed by the prime contractor under specifications No. DC-4825. Installation started with placement of main body and lower bonnet in block 6 in February of 1962, and the embedded parts were completed in block 5A in April of 1962. The ring-follower, gate leaf,

upper bonnet cover, and hoist were installed in outlets No. 1 and 2 in May 1962, and outlets No. 3 and 4 in June of 1962.

In January of 1963, after the installations had been completed, the contractor was operating gate No. 4 for testing and adjustment. During the final checkout, ring-follower gate No. 4 was taken to the closed position but failed to close completely by approximately 2 inches. This gate was being operated by a remote switch to the control cabinet by the crew inside the river outlet pipe. The safety pressure switches had been calibrated and set in accordance with the appropriate drawing. During the long period of erection of the gates, a large amount of residue from sandblasting of outlet pipes upstream of the ring-follower gates had collected in the bottom bonnet of the gate; also drainage water and cement grout had caused sandblast sand residue to solidify to some extent. When the ring-follower on the gate leaf was brought down toward its closed position, the hydraulic thrust collapsed the ring in the bottom of the gates. Measurements on the diameter found the ring was 1 inch out-of-round and warped approximately 3/8 inch. Several methods were tried in an effort to push the ring to its original shape while the leaf was in position in the gate body. All efforts to restore the ring of the leaf follower to roundness while in the gate body failed. The gate was disassembled and the leaf was taken to the installation contractor's shops for repair, during the week of February 11 to 18, 1965. A failure was noted on the downstream stiffener, 3 feet 11 inches up from the bottom and to the left, and at the fabricator's welded joint near the bottom.

During the next 2-1/2 days, the contractor fabricated a structural steel pressing jig and sandblasted away all the coal-tar enamel coating from the section. The true center of the waterway was located by using the top normal machined surface as a reference plane. Radial distances from the center to the inside of the shell were recorded for each 10°.

This measurement was used to determine the amount any segment had to be moved to obtain the desired roundness and to check on any gains made during the pressing operations.

The initial pressures exerted on the section were 50 tons applied near the right springline and 20 tons applied on the inside bottom surface. Measurements taken on the loaded section indicated the horizontal diameter was shortened by 3/8-inch and the lower vertical radius was lengthened by 0.050 inch. When released, the section assumed the original configuration before the pressure had been applied. During this press, it was noted that the weaker top portion bowed out

and away from the center point. For added strength to this portion, the contractor added a 1/2-inch-thick plate, 8 inches wide and 9 feet long, across the top of the section on both the upstream and downstream side. For a more evenly distributed load to the top of the section, braces were added between the pressing jig and the two upper quarter points.

In a 3-day period, various pressures were applied to the section to a maximum of 130 tons on the right springline and 32 tons on the lower inside surface. Higher pressure did not seem practical since the top portion had a tendency to bow out. During the last press of this period, the brass seat was removed and the lower half of the section was heated with propane torches. Temperatures of approximately 550° F. were produced along the bottom, 250° to 300° F. at the

lower quarter points and decreasing to 113° F. at the springline. These operations accomplished a gain of less than one-fourth inch on the horizontal and vertical diameters.

As the follower could not be pressed back into shape, the contractor cut the stiffeners around the circumference of the ring-follower. This method proved to be successful and the ring was brought back to original shape and rewelded. The gate leaf was again installed and the repair work was completed on March 28, 1965. At a later date, the ring-follower gates were put in service and the repair was satisfactory in that leakage was very small on this gate. Subsequently, the pressure limit switch on the other gates was lowered to a safer value which would just operate the gates during initial installation and testing.

210. HOLLOW-JET VALVES. The four hollow-jet valves and controls (figs. 127, 128, 278, and 279) are used to regulate the flow of water from the river outlets. The hollow-jet valves are of cast and welded steel construction and consist of a circular body and a movable needle which forms an annular passage and seals in the throat. The hollow-jet valve is hydraulically operated by a cylinder within the passage which is concentrically positioned by eight radial splitters. Each control cabinet is of steel construction and encloses the control system for two hollow-jet valves. A cable-driven dial-type position indicator for each hollow-jet valve is located on the cabinet control panel to show the percent of opening. The 96-inch hollow-jet valves were manufactured by the Goslin-Birmingham Manufacturing Co., Inc., of Birmingham, Ala., under invitation No. DS-5363. The controls were supplied under invitation No. DS-5503 by the Rucker Co. of Oakland, Calif.

Figure 279.-View looking downstream at No. 2 hollow-jet valve under test, with 10,000 cubic feet per second being discharged from left diversion tunnel in background. P557-420-10685, March 4, 1965.

The four hollow-jet valves were installed at the site by the prime contractor starting on January 15, 1962, and work progressed using conventional erection procedures until completion in April of 1963. The controls were supplied, assembled, and tested by the supplier; only a small amount of field piping work was required to complete the installation. One difficulty noted involved the placement of the flow regulation valves which were inaccessible after assembly of control cabinets. It will eventually be necessary to provide an opening in the cabinets for ready access to adjust the valves. After the first season of operation, the valves were inspected for damage and very little cavitation was noted.

211. GENERAL. Glen Canyon Powerplant was constructed 400 feet downstream of the axis of the dam. This reinforced concrete structure is 649 feet long by 113 feet wide and is 150 feet high above the mass concrete required for a foundation. The structure contains eight 112,500-kilowatt generating units, each driven by a 155,500-horsepower vertical-shaft turbine. The total plant generating capacity is 900,000 kilowatts, or about 81 percent of that authorized for the entire Colorado River Storage Project.

Eight unit bays and a service bay span the width of the canyon with an elevator tower on the west end of the plant and a machine shop downstream of the service bay. The control and office area are housed in a two-story structure placed above the superstructure of units 1 and 2. Placed to a top elevation of 3124.5, the substructure concrete was reinforced around the turbine pits, as well as below the draft tubes, down to elevation 3093.0. Unreinforced mass concrete was placed below this elevation and also upstream of the turbine pits up to elevation 3118.75. The reinforced concrete intermediate structure is from elevation 3124.75 to elevation 3188.50 and contains gallery systems both upstream and downstream of the unit bay crosswalls, and the transformer deck on the downstream side of the powerplant. The superstructure is a structural-steel frame with reinforced concrete walls above elevation 3188.50, and lightweight precast concrete roof slabs for all units except unit 3. Second-stage concrete was used for encasing the turbine spiral cases and for supporting the generators.

First-stage concrete, including the entire closed shell of the powerplant structure, was constructed under the prime contract, specifications No. DC-4825, by Merritt-Chapman and Scott Corp. Second-stage concrete, surfacing concrete, and related work were accomplished by the completion contractor, Ets-Hokin Corp. under specifications No. DC-5750. The generators were furnished and installed under a separate contract, invitation No. DS-5522, with General Electric Co., and the elevators were furnished and installed by Pacific Elevator and Equipment Co., under invitation No. DS-5843.

Air, water and power for the construction work under the prime contract in the powerplant area were furnished from stations on the canyon rim. Air was furnished by supply piping from compressors on the rim. Water was obtained from the wells at Wahweap via the main distribution system. Power was supplied by line from the rim and a temporary distribution system which was installed and moved as the construction work progressed. Construction materials were brought to the work area by high-line cableway or were trucked

through the powerplant access tunnel. Reinforcement was bent and bundled for each lift or placement at the steel yard on the east rim. Reinforcing steel was supported by angle iron and on cast concrete blocks of size to provide required cover. Most of the piping was precut and partially assembled when the piping arrived at the site for installation.

212. EXCAVATION. Excavation for the powerplant structure began in January 1959, with the removal of talus on the left side of the canyon in the machine shop and service bay area. A berm for the machine shop roof at elevation 3239 was excavated, intersecting a minor joint at approximately elevation 3240. As the joint nearly paralleled the face of the canyon wall, rock bolts were placed throughout this section. A rock slab was removed on the left side downstream of the m-line between elevations 3290 and 3195. Foundation benches were cut out of the rock by line drilling methods as the excavation progressed. Benches for the river outlet valve structure and training wall area were cut at elevations 3170, 3161.5, 3151.5, 3141.5, 3131.5, 3118, 3112, and 3108. At the time of the strike on July 6, 1959, powerplant excavation had reached elevation 3110 on the left side.

Drilling and shooting for the powerplant structure began on the right side of the canyon in March 1959. The elevation 3118 bench had been exposed at the time of the strike and excavation had reached elevation 3097. Rock bolts, 6 and 8 feet in length, were used at appropriate locations on both sides of the canyon. Loose rock in the nearly vertical walls of rock excavations was pried off by highscalers working from ropes. Periodic inspections were also made for the purpose of removing any additional rock which became loosened after the initial scaling. Performed concurrently with excavation for the dam, conventional methods and equipment were used for the rock and common excavation in the powerplant foundation area. Briefly, the drilling work was performed by wagon drills and a large bench-type work area was blasted for each round. Large, steel-tracked shovels and draglines loaded the muck into large dump trucks for dumping on the upstream and downstream cofferdams. The upstream cofferdam was located so that a work space was available between the foundation of the dam and the upstream cofferdam, until the excavation level reached the inner canyon bed level.

Following an extended strike of 6 months' duration, excavation work for the dam and powerplant foundations resumed in January 1960. Line drilling, shooting, and mucking for the powerplant excavation began on the left side with the elevation 3110 berm.

Some unsafe rock was removed between elevations 3160 and 3184, between the ex- and g-lines, and berms were exposed on the left side to elevation 3060 under unit bay 8.

Powerplant excavation on the right side of the canyon was resumed at elevation 3097 in the middle of March 1960. Except for the haul, excavation of unit bays 1, 2, and 3 was completed at about elevation 3093 early in May 1960. Bedrock in unit bay 4 was at approximately elevation 3035 which was about 58 feet lower than unit bay 3. Bedrock in unit bay 5 was at approximately elevation 3030. Free-draining gravel material from the excavations was stockpiled at the downstream cofferdam for later use in the tailrace area and between the dam and the powerplant.

During May of 1960, steel dowels were placed in unit bay 1 at elevation 3093, in the theoretical bench at elevation 3109, and in the upstream section of unit bay 3. The ground mat installation also began during this period.

213. FOUNDATION. Once diversion had been completed and the dam keyway excavation had progressed to river level, excavation for the foundations of the dam, penstock supports, powerplant, service bay, machine shop, and river outlet area progressed concurrently. The powerplant was constructed across the downstream portion of an inner gorge in the river bottom rock that extended upstream a short distance from the dam foundation. It was necessary to excavate rock to provide a foundation for the substructure of units 1, 2, and 3. For the remaining units, 4 through 8, mass concrete was placed to provide a foundation. Excavation for the mass concrete foundation was held to a minimum in the river bottom rock, providing keying upstream of the longitudinal centerline of the units.

Originally line drilling and benches would have been used for the service bay foundation but, due to bedding of the sandstone, the benches could not be held. In lieu of the benching, anchor bars were grouted into the canyon wall along with some rock bolting.

A stress relief joint and rock slab in the vicinity of the service bay area mass concrete extending into the left abutment keyway of the dam required remedial measures to assure adequacy for the structure foundation. The rock slab was anchored to the canyon wall from near the a-line to just downstream of the intersection of the 2-inch expansion joint between the dam mass concrete and the service bay with 1-3/8-inch anchor bars on 5-foot centers both ways between approximate elevations 3095 and 3182. The anchor bars were embedded a minimum of 10 feet in sound rock past the relief joints. The anchor bars and relief

joints were grouted in 5-foot lifts as the mass concrete elevation increased. The additional line of 1-3/8-inch anchor bars, as required on the drawings downstream to the a-line and bx-line, were installed in the same sequence as the anchor bars upstream of the a-line.

Two drainage systems were constructed at the concrete-rock contact from downstream of the 2-inch expansion joint to approximately 3 feet upstream of the d-line with gravel and perforated sewer pipe and open-joint sewer pipe. After the anchor bars and grouting had been completed, 3-inch drain holes were drilled through 4-inch pipe embedded in the concrete, through the sewer pipes into the rock, a minimum of 1 foot past the grouted stress relief joint. The purpose of the drain holes was to insure that water pressures would not build up under the rock slab. This phase of the work was accomplished beginning in September 1960 and was completed with the drilling of the required drain holes in March of 1961. Additional anchor bolts were required for the canyon wall but are associated with the dam and are therefore presented in section 161. A series of 1-1/2-inch bolts and drain holes were required to be installed as a part of the canyon wall bolting. These were located between the canyon wall and the service bay and machine shop superstructure walls upstream of the m-line. The work in this area was performed during the fall and winter of 1961 in advance of the remaining wall bolting, as it was necessary that it be completed prior to constructing the superstructure concrete walls.

During June of 1960, movement amounting to 0.08 foot was detected in the foundation rock in unit bays 1 and 3 and in the area of the penstock supports for penstocks 1, 2, and 3. Check points were established throughout the area and were observed for further movement. Additional movement of about 0.07 foot was noted in August, generally towards the east at the upstream edge of penstock support 3C, at the edge of a bench some 58 feet high.

Several steps were taken to stabilize the foundation material. Construction was suspended in unit bays 1, 2, and 3 until all mass concrete in the powerplant was brought up to the level of the unit bay 3 foundation; construction was also suspended on the supports for penstocks 1, 2, and 3 until the adjacent dam and powerplant concrete was brought up to the level of the foundation of the supports for penstock 3; and the size of the fillets on the dam was increased to fill the void between the toe excavation face and the downstream toe of the dam, extending an enlarged fillet from the near vertical cut for the bases of supports for penstock 4 in block 13 to the right abutment. In addition, it was necessary to support the rock wall between penstocks 3 and 4 with concrete buttresses between the powerplant and dam. Four concrete support buttresses