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COSTS

The costs of the principal features are listed below: Dam ..................... $1,991, 474. 40 Spillway ................... 1,065, 198.03 Tunnel and outlet works ............ 619, 711.59 Clearing reservoir site. .........

479, 069.02 Surveys, testing, etc .............

56, 959. 93 Examinations and surveys . ........

22, 912.06 Bridges and roads ..

147, 827.50 Telephone system ............... 1,072. 66

4, 384, 225. 19 The principal unit costs were:

Per cubic yard Tunnel excavation, class 3. ............... $7.02 Spillway excavation, class 2 ......

s... · · · · · · · · . . . . . 56 Spillway excavation, class 3............... 1. 68 Embankment, earth ........... Embankment, rock. · · · · · · ·.... Concrete, plain . . . . . . . . . . . . . . . . . . . . 12. Concrete, reinforced . ................. 17. 39 Spillway lining . . . . . . . . . . . . . . . . . . . . 21.00

east well; and on November 26, 1934, they were located 3.63 feet from the reference line.

Concrete blocks, set in the top of the dam downstream from the corewall, have settled from 0.25 to 0.45 foot, depending on the depth of the fill. One point at the top of the dam, upstream from the corewall, has settled about 18 inches; while a point, established at elevation 2,929, has settled some 30 inches. Both of these points are close to the point of greatest depth of fill.

Observations made on the puddle material at various elevations, through the 3-inch pipes heading in the observation wells, show that there has been little change in the character of the fill in the 9 years since the dam was constructed. Those portions, which were semiliquid when placed, are still in a semiliquid condition; while at points where the fill was fairly solid samples can only be obtained by scraping them through the pipe. A detailed analysis of conditions in the embankment core was included in an article on Puddle Core Investigations at Tieton Dam, by Ivan E. Houk, published in Engineering News-Record, September 30, 1926.

The drains beneath the rock fill on the downstream side of the dam have been collected largely at one point where a record is kept of seepage water. The maximum reached was 0.2 second-foot, about half of this running continuously.

TESTS AND OBSERVATIONS ON EMBANKMENT

BIBLIOGRAPHY

When the dam was built monuments were located in the rock abutments, well back from the dam on the line of the corewall; and two observation wells were built on the lower side of the corewall. Observations have been made on the movements of the corewall and on the settlement of the fill above and below the corewall. Those taken during the summer of 1934 show that the corewall, at the elevation of the top of the parapet, 2,937.0, had a maximum deflection downstream of 0.98 foot at approximately station 6+00. The records show that the wall moves downstream as the water surface in the reservoir rises, and returns a portion of this distance when the water falls. Brass plugs were set in the bottom of the observation wells when they were built, 3.50 feet downstream from the control line between the monuments. The maximum distance recorded for these points was 3.83 feet for the west well and 3.73 feet for the

Tieton Dam, Yakima Project, Washington. Reclamation

Record, October 1921. Building the Tieton Dam. Pacific Builder and Engineer,

Jan. 26, 1923. The World's Highest Earth Dam. Excavating Engineer,

February 1923. Tieton Dam Construction. Reclamation Era, February

1926. Puddle Core Investigations at Tieton Dam. Engineering

News-Record, Sept. 30, 1926.

GUERNSEY DAM

NORTH PLATTE PROJECT, NEBRASKA-WYOMING

BY L. W. BARTSCH, ASSISTANT ENGINEER, BUREAU OF RECLAMATION

GUERNSEY DAM, located about 2 miles northwest of Guernsey, Wyo., is a feature of the North Platte Project for irrigating lands adjoining North Platte River from Guernsey, Wyo., to Northport, Nebr. Pathfinder Reservoir, the main storage reservoir for the North Platte Project, is located about 45 miles southwest of Casper, Wyo., approximately 160 miles upstream from the point of diversion. Guernsey Dam, located only 9 miles above the point of diversion, impounds the inflow below Pathfinder Reservoir and provides closer control of water for diversion into the irrigation canals. In addition, the Guernsey Dam provides a maximum head of 90 feet for the development of electrical power, which, with the electrical energy developed at the Government power plant at Lingle, Wyo., serves the project and towns in the North Platte Valley from Casper, Wyo., to Scottsbluff, Nebr.

Guernsey Reservoir has a surface area of 2,340 acres at maximum water surface elevation 4,420. The original maximum capacity of the reservoir was 67,570 acre-feet; but a reservoir silt survey made in 1937, approximately 9 years after completion of the dam, showed a reduction in reservoir capacity to 54,610 acre-feet.

The drainage area above Guernsey Dam comprises 16,200 square miles with an annual mean run-off of 1,700,000 acre-feet.

The dam site is located in a comparatively precipitous canyon. Solid rock, consisting of sandstones of varying degrees of hardness, together with limestone and some shale and with occasional streaks of iron ore, is generally near the surface at the dam site and is exposed in irregular cliffs over portions of the abutments. Solid rock in the stream bed lies beneath a layer of sand, gravel, and boulders, so deep as to render closure between the dam structure and the underlying bedrock impracticable.

Test holes were carried to a depth of 100 feet below the stream bed surface, but failed to reach solid rock. This condition was a dominant factor in deciding the general design of the structure.

THE DAM The dam is a composite structure of sluiced clay, sand, and gravel, covered on the upstream slope with a 3-foot layer of rock riprap and on the downstream slope with a heavy rock fill. The embankment extends 30 feet below, and 75 feet above original stream bed, with an over-all

height of 105 feet and a crest length of 560 feet. The dam has a total volume of 561,260 cubic yards, of which 365,000 cubic yards are earth fill and the balance rock fill. The structure has a 3:1 slope on its upstream face and a slope on its downstream face varying from 2:1 between elevations 4,430 and 4,390, and 8:1 from elevation 4,390 to elevation 4,354.6. The central portion of the dam is a clay-puddled core, founded in an open trench 30 feet below the river bed and extended continuously upward through the embankment to the crest. The trench in which the puddled core was founded has a bottom width of 10 feet and side slopes of 132:1. On each side of the clay core is the sluiced sand and gravel fill, the upstream and downstream slopes of which are covered by the rock fill and riprap.

To tie the embankment into the rock abutments and prevent seepage along the planes of contact, three concrete cutoff walls were provided on either side of the river channel. These walls were keyed not less than 2 feet deep into the solid rock abutments and built not less than 5 feet high above the rock surface. They extended from 15 feet below the original river bed to the top of the dam on either side. The trenches in which the walls were placed were backfilled with puddled clayey material, and this material was carried into the dam embankment over and around the tops of the cut-off walls to a minimum depth of 5 feet.

The crest of the dam is finished with a concrete parapet wall extending 3 feet above the top of the embankment on the upstream side and with a low concrete curb on the downstream side. A roadway, 26 feet wide, is provided between the parapet and downstream curb. The design of the dam first contemplated, provided for a percolation slope of 8:1 through the structure. This was changed to 9:1 during construction, by the addition of the level portion of the rock fill at the downstream toe.

The accompanying drawing and photographs show the general plans, elevations, and sections of the dam, also the general features and dimensions of the related structures.

RIVER DIVERSION North Platte River at the site of Guernsey Dam has a large annual run-off, the maximum of record being about 3,200,000 acre-feet measured at the Orin junction, 40 miles upstream. The maximum recorded rate of discharge at the dam site was 30,000 second-feet, occurring in June 1908. During construction it was necessary to pass irrigation water

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SPILLWAYS

for the North Platte project and to meet other water rights. These conditions, and the fact that the construction period was to extend over more than 1 year, made necessary ample provision for river discharge.

River diversion during construction was accomplished by a large tunnel, excavated through the solid rock of the right abutment, approximately on the level of the original stream bed. This tunnel was the first work of construction. It is 1,070 feet long with 273 feet at the upstream end consisting of a 25-foot horseshoe section, and the balance, a 30-foot horseshoe section. Suitable portal structures were provided at each end, the upstream portal providing for permanent closure at the end of diversion and the downstream portal being constructed for permanent use as spillway and sluiceway outlets. The tunnel was lined throughout with concrete. The designed thickness of the concrete was 18 inches; but due to the varying, laminated, and seamy nature of the sandstone and limestone, the overbreakage was large and necessitated increasing the thickness of the concrete lining by 47 percent.

The rock excavation from the tunnel was placed directly in the downstream portion of the dam, building out from the abutments across the river channel and restricting it until the tunnel was completed, when final closure of the rock fill across the river channel was made. Thus the tunnel muck was used as a downstream cofferdam, which later became part of the permanent dam. The excavation from the intake and from the intake portal was used for the upstream cofferdam and for the upstream toe of the dam.

Two spillways were provided, a 50- by 50-foot Stoney gate structure, located at the north end of the dam, and an automatic drum gate spillway on the south side of the dam. The north spillway provides the main facility for passing large flood discharges; also for regulating irrigation outflow. It has a discharge capacity of 52,000 second-feet with the gate wide open and the reservoir water surface at the maximum elevation 4,420. The structure has a trapezoidal, concretelined discharge channel, 585 feet in length, with a bottom width of 25 feet, side slopes of one-half horizontal to one vertical, and a depth of 40 feet. The spillway channel downstream from the regulating gate is in solid rock.

Upstream from the gate the approach channel is formed by a vertical, reinforced concrete, counterforted retaining wall, 66 feet high at the maximum point. The foundation rock along the toe of the retaining wall, across the channel under the control gate and behind the wing wall on the north side, was pressure-grouted to avoid leakage. The concrete lining of the channel is anchored to the rock by 194-inch anchor rods at 10-foot centers both ways, grouted 5 feet into rock and firmly attached to the steel reinforcement in the lining, which consisted of 7-inch steel bars at 15-inch centers both ways. Tile drains are provided at 10-foot intervals beneath the lining on the sides and bottom. These discharge into a 30-inch square manway drain under the lining along the center line of the channel, extending from the control gate to the downstream limits control for each gate is accomplished by floats located in float chambers in the end piers. The floats actuate 24-inch needle valves which, in turn, regulate the water pressure in the chamber beneath the drum gates by controlling the release of water from the chamber. The chamber is connected with the reservoir by means of a controlled opening. Manual operation of the gates is also provided.

POWER STRUCTURES

of the channel. A concrete bridge with a 16-foot roadway was constructed over the spillway channel at the gate structure.

The control gate is a structural steel, vertical, Stoney roller gate, 50 feet 9 inches high by 54 feet 794 inches wide. The gate leaf is built up of 12 plate-steel girders, 6 feet deep, laid horizontally and suitably braced and covered on the upstream side with a %6-inch steel skin plate. The gate operates on six sets of caterpillar rollers, rolling on H-beam tracks at the sides of the gate. The web of the H-beam track provides the flexibility required to amply care for any deflection in the gate, or other movement that might throw the bearing surface of the rollers out of plane. Each of the three lower caterpillar roller sets contain 24 rollers of chilled cast-iron, 8 inches in diameter by 12 inches long, and each of the three upper sets contain 15 rollers of the same size. The gate is rendered waterproof by the use of brass pipe staunching rods that move with the gate. The gate weighs 434,000 pounds and is counterweighted by concrete blocks having a total weight of 374,000 pounds.

The gate is suspended from either side by large metal link chains which pass over the operating machinery to the counterweights placed in concrete chambers on either side of the gate. The chains are constructed of high-tensile bronze pins, 5 inches in diameter and 17 inches long, spaced at 10-inch centers and connected by four lines of 1- by 9-inch high-carbon steel plate links with a combined cross-sectional area of 36 square inches. The chains are constructed with extreme accuracy and close tolerances. Each chain has a total length of 66 feet 2 inches and a unit weight of 238 pounds per linear foot.

Gate-operating machinery is located directly over the gate. Two specially designed hoists are provided at either side of the gate and are connected by a line shaft through which they are driven by a centrally placed electric motor. A gasoline motor stand-by unit is provided for use during failure of the electrical unit. The gate-operating machinery is located in the superstructure of the gate chamber, in a house 14 feet 6 inches wide by 72 feet long. A 5-ton crane is installed over the operating machinery for maintenance and repair work. The position of the gate can be readily controlled to within 0.01 foot. Provision for its remote control is made in the power plant.

The south spillway is an automatically operated structure, consisting of two 64- by 1414-foot, structural steel, floating drum gates installed on a concrete crest at the right abutment of the dam, over the diversion tunnel. Water discharging over the spillway drops through a 31-foot diameter vertical shaft into the diversion tunnel. The maximum discharge capacity of the south spillway is 30,000 second-feet.

Control mechanisms for the drum gates are contained in the concrete piers at each end of the structure and in passageways through the concrete crest. Individual automatic

The intake gate and the trashrack structure for the power water are built on the right abutment of the dam, above the diversion tunnel and upstream from the automatic drumgate spillway. The control gate is placed parallel to the hillside and is built on a slope of 45°. It consists of a single 20- by 26-foot, Stoney roller gate, electrically operated by a geared hoist, connected to the gate by 6-inch diameter solid steel stems. These hoists are located in a house, 13 by 9 inches wide by 27 feet long, similar in design to the superstructure of the north spillway gate. The trashrack is built above and beyond the gate and provides an entrance area of 4,460 square feet. The trash bars are 4- by 36-inch steel bars, spaced to provide a clear opening of 3 inches.

The power intake structure connects to the 25-foot diameter portion of the diversion tunnel by a concrete-lined, circular shaft, 20 feet in diameter. At the junction of the power intake tunnel with the diversion tunnel two massive concrete plugs were placed in the diversion tunnel. One plug is constructed immediately upstream from the junction point of the tunnels. It provides the main watertight closure of the tunnel to the reservoir water. No openings are provided through this plug. The other plug is constructed downstream from the junction point of the power intake and diversion tunnels, but upstream from the junction of the spillway shaft and diversion tunnel. The downstream surface of this plug is suitably shaped to form a transition between the spillway shaft and tunnel. Three 5. by 5-foot hydraulically operated slide gates are installed in this plug.

The two plugs form a desilting chamber through which the power water passes with relatively slow velocity, depositing the silt, which is then removed from the chamber by opening the three slide gates in the downstream plug. The operating mechanism for the sluice gates is contained in an enclosed chamber over these gates, and access to this chamber is by a passageway and stairs leading from the piers of the drum gate spillway structure.

The power penstock consists of a 12-foot diameter circular, concrete-lined pressure tunnel, leading from the desilting chamber through the solid rock of the right abutment past the dam to the power plant below. The center line of the power tunnel runs parallel to the center line of the spillway tunnel, 25 feet above it and 42 feet nearer the river. The penstock tunnel is 662 feet long. Its concrete lining was designed to be 10 to 15 inches in thickness. The over

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breakage in the rock that was replaced with concrete was 42.8 percent, computed on the basis of a 15-inch lining. The lining was placed by a one-cubic-yard concrete gun, discharging through a 6-inch delivery pipe. Admixture was added to the concrete to the extent of 3 percent of the cement by weight.

The concrete lining of the pressure tunnel is not reinforced. Ability to withstand the water pressure is insured by the thorough pressure grouting of the surrounding rock. For this purpose 111 holes were drilled radially into the rock, to an average depth of 10 feet, spaced about 16 feet apart. Each hole was first tested with water, then with a batch of thin grout, after which fine sand was added up to a 1:1 mixture. The total amount of grout forced into the holes was 60 cubic yards, a quantity equivalent to 0.059 cubic foot per square foot of tunnel surface. The grouting operations were apparently successful, as no extensive seepage has been detected since it was put into operation.

At its outlet end the power tunnel is connected to a steel penstock leading to the turbines in the power house. The steel penstock branches to serve the two power units.

Immediately above the branch a surge tank is provided to prevent excessive pressure rise in the long penstock. The surge chamber is cylindrical in shape, of riveted plate steel, 22 feet in diameter, 85 feet high, and is supported on a massive concrete base. A maximum static head of 90 feet is available at the power plant.

The power house is a reinforced concrete structure, 72 feet 6 inches long by 50 feet wide and 44 feet high above the main operating floor. The turbines and discharge draft tubes lie below the floor. The present installation consists of two 3,400-horsepower turbines, direct-connected to two 3,000 kilovolt-ampere generators with direct-connected exciters. The turbines are designed for an average pressure head of 65 feet and a speed of 240 revolutions per minute. Electricity is generated at 2,300 volts and stepped up to 33,000 volts for long-distance transmission. The present design provides for the future construction of a second pressure power tunnel on the opposite side of the spillway tunnel, and for the installation of two more power units similar to the present units in a house to be extended downstream from the present house.

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