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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.

The tailrace from the power plant discharges in the river at a point upstream from the normal downstream toe of the dam. It was necessary to provide special construction at this point to avoid weakening the dam and reducing its percolation factor. This was accomplished by excavating the tailrace to a depth of 10 feet below its required bottom and placing thereon an 18-inch layer of screened gravel to serve as a drain and filter for seepage water. An 8-foot 6-inch layer of heavy rock fill was placed over the gravel laver.

CONSTRUCTION

The gravel and clay fill of the dam was placed by the semihydraulic method. The material was transported from the borrow pits by trains, and dumped from trestles on the upstream and downstream sides of the embankment. A pool of water was formed between the piles of dumped material, and the finer materials sluiced into the pool by a hydraulic giant mounted on pontoons floating in the pool. The finer materials sluiced into the pool form the puddle core, and the coarser, gravelly, material is left in the upstream and downstream portions of the embankment. The borrow pits from which the embankment material was obtained contained clay, sand, and gravel in about the right proportions for the embankment, except that additional clayey material was added during construction to furnish sufficient extra clay required for the puddled core. The rock material excavated from the tunnels, the spillways, and from other structures was placed on the upstream and downstream slopes of the embankment.

Plans called for placing an earth blanket on the reservoir floor, immediately above the upstream toe of the dam. This earth blanket was partially placed, as contemplated; but was largely secured by the natural settling of silt from the water impounded above the upstream cofferdam during the diversion period.

The north spillway gate leaf was assembled on a trestle built 15 feet above the channel floor. For transferring the weight of the gate to the counterweights, the counterweight wells were sufficiently filled with sand to allow the chain connection to be made. When the chain was connected to the counterweight stem, the sand was removed from the bottom of the counterweight well by an air jet, allowing the counterweight to settle slowly until it took the full weight of the gate. The hoists then raised the gate and the trestle support was removed.

The Guernsey Dam and power plant were constructed under contract by the Utah Construction Co., of Ogden, Utah. Work was commenced in May 1925, and completed in January 1928.

COST

The principal items and approximate quantities of work involved in the construction of the dam and power plant were as follows:

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BIBLIOGRAPHY

Building the Guernsey Irrigation and Power Dam. F. F.

Smith, Eng. N. 100: 264-8 Feb. 16, '28, illus. Guernsey Dam Contract Awarded. New Reclamation

Era 16:95 June '25. Guernsey Dam Helps Irrigate Lands in North Platte

Valley. C. H. Vivian. Comp. Air M. 33: 2373-7 April

'28, illus.

Guernsey Dam, North Platte Project, Nebraska-Wyoming. W. H. Nalder. New Reclamation Era 19:184-7 December '28, illus.

Guernsey Dam; Relation to Water Supply and Power. A. Weiss, New Reclamation Era 16: 30 February '25.

Guernsey Power Plant, North Platte Project, NebraskaWyoming. H. F. McPhail. New Reclamation Era 19: 60-2 April '28, illus.

Guernsey Surge Tank, North Platte Project, NebraskaWyoming. R. E. Glover. New Reclamation Era 18: 136-7 September '27, illus. Same: Hydraulic Eng. 3: 20, 30 November '27.

New Slackline Cableway Bucket Used on Guernsey Dam. West. Constr. N. 1: 33 Dec. 10, ?26, illus.

North Platte Irrigation Project. E. H. Simpson. Eng. World 31: 3-5 July '27, illus.

North Spillway Gate and Hoist, Guernsey Dam, Wyoming, P. A. Kinzie. West. Constr. N. 4: 174-82 Apr. 10, '29 illus.

Power and Irrigation Work Financed by PWA. Eng. N. Ill: 251-3 Aug. 31,'33, illus.

Sluiced Gravel Forms Main Embankment for Guernsey Dam. Const. Methods 10: 26-8 April '28, illus.

ECHO DAM

SALT LAKE BASIN PROJECT, UTAH

BY O. L. RICE, ENGINEER, BUREAU OF RECLAMATION

ECHO DAM was the first unit constructed on the Salt Lake Basin project in Utah. It was built across Weber River about 1 mile upstream from the town of Echo, a junction point on the main line of the Union Pacific Railroad. The dam is located about 45 miles by highway from Salt Lake City. It provides a storage reservoir which is used almost wholly as a supplemental water supply for 80,000 acres of irrigated lands in the Ogden and Utah Lake Valleys which arc supplied with water under existing canals, taking water from the Weber and Provo Rivers.

The development of the supplemental water supply created by the reservoir requires exchanges of Weber River water for Echo Reservoir storage and the diversion of certain surplus flood waters from the Weber River watershed to the Provo River watershed. The diversions are made through the Webcr-Provo diversion canal of 210 second-feet capacity, constructed as a unit of the Weber River division of the Salt Lake Basin project. The diversion works are located on Weber River near Oakley, about 24 miles upstream from Echo Dam.

The building of Echo Dam necessitated the relocation of the Park City branch of the Union Pacific Railroad and the Lincoln Highway around the cast side of the reservoir; also the reconstruction of a portion of the Coalville City water main and the construction of a farm road around a portion of the west side of the reservoir as well as reconstruction of portions of telephone and electric lines located in the reservoir and borrow pit areas.

RESERVOIR

Echo Reservoir has a storage capacity of 74,000 acre-feet and a drainage area of 730 square miles. The lake formed by the dam is 4}., miles long, with a maximum width of 1 mile and a surface area of 1,470 acres at the normal water surface elevation 5,560. The average annual run-off into the reservoir is about 280,000 acre-feet.

A contract with Heiselt Construction Co., dated April 26, 1928, provided for the clearing of the reservoir site. All trees and brush over 5 feet in height lying below the flow line were cut as close to the ground as possible, and all logs, trees, brush, and combustible debris not salvaged by the contractor were burned.

DAM SITE

The dam site lies at the lower end of a flat mountain valley, at a point where the canyon walls are relatively close together. The foundation rock consists of Wasatch conglomerate on the left abutment and river bottom portions, and grades into a sandstone on the right abutment. The bedrock lies at an almost constant elevation in the river bottom and rises abruptly on the right abutment. At the left abutment the rock surface rises rather abruptly for a height of approximately 50 feet, then flattens out again. The conglomerate is made up of coarse sand, fine grit, small pebbles, and cobbles up to 6 or 8 inches in diameter, all weakly cemented together. Both the conglomerate and sandstone are soft, somewhat porous, and break down rather readily due to weathering.

A considerable depth of overburden lies above the foundation rock, except for a narrow section cut by the river. The depth to bedrock is about 26 feet below the stream bed and increases to approximately 65 feet at the east half of the dam where a large terrace of alluvial material has accumulated.

The upper portions of the overburden consist of clay intermixed with coarse materials forming a reasonably tight section, while the bottom portion consists of porous sediments of sand and coarse materials varying from thin layers to layers several feet in thickness.

Some preliminary testing was done at the dam site as early as 1905, but the major part of the testing was accomplished during the years 1924 to 1926. Suitable embankment materials were located at various points near the dam site. Concrete aggregates were located in the river channel below the dam.

THE DAM

The dam consists of a moistened and rolled embankment of clay, sand, and gravel, with a heavy downstream section of gravel, cobbles, and rock fill. The upstream 3:1 slope was covered with a 4-foot layer of dumped conglomerate riprap, and the berm and 5:1 slope portions were covered with a 2-foot layer of sand and gravel excavated from the cut-off trench. The maximum height of the dam is 125 feet above stream bed or 151 feet above bedrock. It has a crest mcnt, and the relocated railroad and highway are located at the right abutment. The right end of the dam is turned upstream into a projecting face of the abutment, to provide suitable contact with the abutment and to minimize the highway fill at itsjunction with the dam. The railroad grade is about 25 feet below the crest of the dam at the axis, and a puddled core was constructed in the central portion of the highway to protect the railroad against seepage from the reservoir.

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The axis of the dam was located somewhat parallel to the upstream face of the terrace and at such distance that the cut-off trench, extending to bedrock, would lie largely in the river bottom without increasing the cut-off trench excavation or quantity of dam embankment.

The concrete cut-off wall was constructed continuously across the dam from the center of the highway at the right abutment and to a point 206.5 feet into the left abutment, beyond the center line of the spillway. The portion of the cut-off in the river bottom lies in the center of an open

length of 1,887 feet, including the spillway channel, a crest width of 25 feet at elevation 5,570, and a base width of 830 feet at the maximum section, exclusive of the upstream dry earth blanket. Concrete parapet and curb walls are constructed along each edge of the crest.

The upstream slope is 3:1 from the crest to a berm 20 feet in width at elevation 5,482, and 5:1 from the edge of the berm to the ground line. A dry earth blanket with a 20:1 slope extends approximately 300 feet upstream from its intersection with the 5:1 slope at elevation 5,462.14. The downstream slope is 2:1 from the crest to a break in slope at elevation 5,477 in the river bottom and elevation 5,499.2 on the sides adjacent to the river channel, and 6:1 extending to the ground line, except for the section in the river bed which breaks again to a 1 %: 1 slope near the ground line at the downstream end. Toe drains of 8- and 12-inch drain tile were laid in gravel-filled trenches excavated at the downstream toe of the dam.

Outlet works and spillway are located at the left abut

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