trench with 20-foot bottom width and 1:1 side slopes excavated to bedrock. Sections of vertical side trench, 21⁄2 feet in width, located in the center of a smaller open cut and extending 1.5 feet into bedrock, were excavated at both abutments where the previous layer was relatively. thin and where bedrock occurred at a depth of approximately 40 feet. A stoped concrete cut-off, 4 feet in width, was constructed at the left abutment where the depth of overburden exceeded 40 feet. The stope was excavated 1.5 feet into the foundation rock and extended through the porous layer a minimum of 5 feet into the overlying impervious material. It was entirely filled with concrete and grout.

A reinforced concrete cut-off wall, 12 feet high, 12 inches thick at the top and 18 inches thick at the base, with footings approximately 3 feet wide extending 1.5 to 4 feet into excavated trenches in the bedrock, was constructed in the open cut-off trench. The vertical side trenches were backfilled with concrete to a minimum of 5 feet above the porous layer and backfilled with puddled clay from the top surface of the concrete to the bottom of the excavated trench above.

A section of the cut-off at the right abutment was begun as a vertical side trench; but, before completion, a slide occurred destroying the compaction of the foundation and the section was changed to a cut-off trench in open cut. An additional cut-off wall was constructed to further insure safety against seepage along the rock cliff at the right abutment.

The base of the dam was stripped of unsuitable foundation materials. Pockets of soft silt mixed with clay and humus were encountered in the river bottom and were entirely removed before placing the earth fill.

It was originally contemplated that the downstream. portion of the dam, beginning at the lower 1.6:1 earth fill slope, would be constructed of gravel and cobbles obtained from necessary excavation or from borrow. During the progress of work it developed that insufficient suitable materials were available and conglomerate rock fill was substituted to complete the section. The principal quantities involved were as follows:

capacity of 15,000 second-feet at normal water-surface elevation of 5,560. The discharge is controlled by four 18by 17-foot, counterbalanced, radial gates, located near the axis of the dam. A transition begins at the downstream end of the gate structure and terminates at the chute section having 1:1 side slopes.

The chute is built on a steep slope and terminates in a stilling basin, serving both the spillway and outlet works. The stilling basin has a bottom width of 40 feet and a depth of 31 feet, the bottom being 17 feet lower than the outlet channel to the river which is an unlined channel with a 30foot bottom width and 11⁄2: 1 side slopes.

The gate structure and upper portion of the chute section rest on earth materials, and the lower portion of the chute section and major portion of the stilling basin are founded on conglomerate rock. The portion of the spillway resting on earth materials was thoroughly drained with sewerpipe drains, laid in a gravel trench; also by a 6-inch layer of screened gravel laid under the spillway floor and sides. Drainage in the stilling basin was provided through 2-inch weep holes at 5-foot centers, drilled through the concrete lining to the rock surface. Counterforted side walls were designed for the upper and lower portions of the spillway where active earth pressures exist.

An extensive cut-off, located directly above the stoped cut-off wall, was constructed as a collar around the spillway gate structure, extending 21 feet below the floor and 30 feet on each side of the spillway to provide additional safety and to prevent seepage from the reservoir.

The stilling basin floor was lowered 11 feet and the basin lengthened 60.07 feet after the spillway excavation had begun, due to the absence of substantial rock foundation. A section of rubble concrete paving was constructed at the end of the stilling basin to protect the portion of the bottom and sides of the channel founded on earth.

The two center gates operate automatically through electrical contact produced by actuating floats installed in wells in the two outer piers. The operating mechanism consists of electrically driven gear hoists with gas engine installation for emergency control. The water level in the piers is maintained through 4-inch piping leading to the reservoir. The automatic gates are raised or lowered in increments of 4 inches in accordance with a rising or falling reservoir. A change of water surface of 0.01 foot produces the electrical contact.

Electric lines, together with the necessary transformers, are connected with the Utah Power & Light Co.'s power line near the left end of the dam.

OUTLET WORKS

The diversion tunnel, 838 feet in length, located at the left abutment, was designed to house the outlet works after serving its purpose for diversion. The upstream portion

of the tunnel, located between the trashrack structure and gate chamber, is a 14-foot horseshoe tunnel. The downstream portion, between the gate chamber and needle valve structure, is a modified horseshoe 18 feet wide by 12 feet high. The size of the tunnel was largely dictated by the diversion requirement of 5,000 second-feet. The tunnel was lined throughout with concrete of 12-inch average thickness. The first 33 feet were reinforced with 4-inch reinforcement bars, due to overbreakage at the portal. The 14-foot horseshoe section was grouted through fifty-three 2-inch holes of 8-foot average depth, drilled through the concrete lining into the surrounding rock, 1,085 cubic feet of grout being required.

The outlet works consist of two 5- by 6-foot high-pressure, hydraulically operated, slide gates with metal conduit lining, placed in a tunnel plug in the gate chamber located beneath the crest of the dam. Two 72-inch, plate steel, riveted outlet pipes, supported on concrete cradles, extend from the gates to the needle valves at the downstream end of the tunnel. The 60-inch, internal differential needle valves discharge into the stilling basin at the bottom of the spillway. They are located in a concrete structure over which is constructed a concrete house with a title roof. A 6-foot diameter, concrete lined, vertical shaft extends from the gate chamber to the crest of the dam, where a concrete emergency gate house with tile roof is located. Control works for the high-pressure gates are located in both the emergency gate house and needle valve house. The needle valve control works, together with a gantry crane, are installed at the needle valve house. An oil heater is also installed in the valve house, to prevent freezing during cold weather.

Drainage of the pipe section of the tunnel is provided through an 8-inch sewer-pipe drain, laid in a gravel filled trench under the invert of the tunnel. External pressure is relieved by 2-inch drilled weep holes at the intersection of the side wall and invert. The gate chamber is drained by an interconnected system of wooden V-drains, tile, and cast-iron pipe drains, leading to the 8-inch sewer-pipe drains. The tunnel drain is connected to a cast-iron pipe drain at the needle valve structure. It leads around the structure to the stilling basin. An additional cast-iron pipe drain, serving the valve structure, is laid in the same trench with the tunnel drain.

CONSTRUCTION METHODS

The major part of the construction work on Echo Dam was performed by A. Guthrie & Co., under specifications no. 463. Work was begun December 12, 1927, and completed October 7, 1930. The contractor's camp, equipped to accommodate 200 men, was located on a bench downstream from the toe of the dam.

Preliminary operations consisted of stripping portions of the river bed and spillway stilling basin to provide access to

the tunnel and space for embankment materials in the dam. Excavation of the tunnel was started at the inlet end March 9, 1928, and at the outlet portal April 25, 1928. A 7- by 7-foot bore was first excavated through the upstream portion of the tunnel for a distance of 424 linear feet, while at the downstream end the full section was excavated. The tunnel was "holed through" May 29, 1928. Excavation was continued toward the upper portal and was completed June 16, 1928. The full size bore was excavated by a tunnel mucker, loading into mine cars hauled by gas locomotives to the dam or wasted as directed.

Rock encountered in the tunnel varied from a fair grade of conglomerate rock, with a matrix varying from red shaley clay to grey sandstone, to a light colored shaley rock of soft nature. Two short sections of the tunnel were timbered. Drilling of the rock was readily accomplished with water drills. The overbreakage was heavy, extending as much as 8 feet into the roof of the tunnel.

Aggregates for the concrete lining as well as for other concrete work in the dam were obtained near the river channel, about one-fourth mile downstream from the lower tunnel portal. The aggregates were hauled in mine cars by gas locomotives, to a concrete mixer located above the lower portal. An inclined tramway was used to elevate the mixed concrete to the top of the gate shaft. The concrete was then dumped into a receiving hopper which in turn dumped through an 8 inch steel pipe to a lower charging hopper. A 3-cubic-yard pneumatic concrete gun, mounted on rails in the tunnel, conveyed and placed the concrete lining.

Lining operations began August 1, 1928, near the lower portal, and on August 3, near the upper portal, the pours then being alternated between the lower and upper portions of the tunnel. The side wall and arch portions of the tunnel were placed first. The forms consisted of 2by 4-inch sheet steel covered lagging, supported on wooden ribs spaced at 16-inch centers. The forms were mounted on a small jumbo and were hinged at the top to make them collapsible. Jacks were provided to raise the forms into place. A 4- by 4-inch keyway was placed between the side walls and invert. The lining was completed October 12, 1928. Tunnel grouting was accomplished with a small grout machine, beginning first with a thin mixture of cement and water, to fill the fine cracks in the rock, and later using a thicker mixture consisting of cement, water, and very fine river sand. A maximum grouting pressure equal to the reservoir head was used.

The trashrack structure was constructed prior to river diversion, and a 30-foot intake channel was extended from the trashrack structure to the river channel. A small dike was constructed and the river diverted October 29, 1928. Since the stilling basin concrete was not then completed, a 5- by 6-foot wooden flume, supported on wooden bents, was constructed from the tunnel portal to the excavated

outlet channel below the stilling basin. The maximum diversion discharge of 2,550 second-feet occurred during the 1929 season, after the flume had served its purpose.

A channel was excavated against the right side of the river bottom, to permit cut-off and stripping excavation to be made and to provide space for the placing of earth fill and rock fill obtained from required excavations prior to the diversion of the river through the tunnel. As soon as the river was diverted, the stripping and cut-off excavation was completed and embankment placed below the cut-off trench to elevation 5,480, prior to closing down for the winter, December 7, 1928. Earth placing was resumed March 18, 1929, and by the end of the season the earth section was completed to elevation 5,525. It was finally completed during the summer of 1930.

The cut-off excavation in open cut was made with a dragline, the suitable coarse materials being hauled to the gravel and cobble fill section of the dam with tractors and trucks.

The major portion of the stoped section of the cut-off at the left abutment was excavated and concreted from a shaft sunk at the end of the spillway cut-off. The top portion of the stope was excavated through a heavy clay, the swelling characteristics of which required heavy timbering. Concrete was placed in the stope by a concrete gun. Grout pipes were placed at the high points of the excavation and a tight seal was made between the concrete and earth. The timbering and lagging were removed prior to or during the concreting operation. A relatively small amount of seepage

water entered the cut-off trench and was diverted to sumps where it was pumped out using 6- and 4-inch pumps.

Four borrow pits for earth materials were available near the dam site. The major portion of the earth fill was obtained from a borrow pit located upstream from the left abutment. The material consisted of an unassorted mixture of well-graded clay, sand, and gravel, producing a water tight dense fill. The excavation in the borrow pits was made with 14 to 11⁄2-cubic-yard shovels, loading into ten 5-cubic-yard trucks, eight 7-cubic-yard tractors, and seven 12-cubic-yard wagons, hauled by 60-horsepower caterpillar trucks. Five shovels and twenty-five hauling units were the maximum number used at one time from both the earth and rock pits. The wagons had the ability to dump in layers of the proper depth by adjusting the tail gate.

Rolling equipment consisted of tampers having 7-inch tamping knobs, hauled by a 60-horsepower caterpillar. Ordinarily, the surface of the preceding layer was sprinkled with water, the material dumped, sprinkled again in the piles, then dozed to an approximate 11-inch layer, reducing to 8 inches after compaction, and sprinkled again if necessary to secure the proper amount of moisture for maximum compaction with the rolling equipment used. The tamping knobs on the roller started the compacting process at the bottom of the layer, gradually rising to the top when the material was fully compacted and the knobs rode on the surface.

The moisture content varied considerably in the borrow pits and considerable judgment had to be exercised to

obtain the additional amount of sprinkling required. It was found that maximum compaction was obtained when the material was damp enough to make traction difficult for the rubber-tired trucks. The moisture content varied between 10 and 18 percent, depending on the character of the materials. The compacted density of material in place varied from 107 to 141 pounds per cubic foot. It was found that to secure uniform wetting and uniform compaction it was necessary to keep the surface of the dam level at all times. This was done by means of a 12-foot blade machine which was used every second or third layer.

In constructing the dam, the location in which the various grades of materials were deposited was given attention. The downstream portion of the dam was constructed of the coarser material, while the fine clayey material was kept to the upstream third. The finer material was placed in the cut-off trench by depositing at equal heights on each side of the cut-off wall. The portion of fill near the wall was compacted by hand tamping methods. The earth fill was puddled against the exposed rock face at the left abutment, to secure intimate bond with the rock.

Riprap and rock fill was obtained from two rock quarries located on the left or west side of the river, the lower quarry being a short distance upstream from the upper tunnel portal and the upper quarry about one-half mile west of the dam, at the head of a draw leading toward the dam. The rock in the lower borrow pit was drilled with a wagon drill and a large area was drilled and blasted as a unit. The upper borrow pit, which had a steep exposed face, was shot from "coyote" holes drilled into the hillside. The upper quarry contained an excess of fines after being shot and about 26,000 cubic yards were necessarily wasted.

The rock fill was placed in 12-inch layers which were sprinkled with water to break down the rock having a soluble or weak matrix. Although it was tightly packed, it was free draining. The larger rock particles were dozed to the outer slopes.

Riprap, which was composed of the larger rock fragments of quarry materials, was secured mostly from the upper quarry. Roads were constructed at intervals down the 3:1 slope from which the riprap was dumped. The rock was then spread, where possible, using a bulldozer. Numerous mechanical methods were tried for spreading the rock, but without much success.

The spillway was excavated using a shovel in the stilling basin and gate structure and a dragline for the chute section. All materials from this excavation, except stripping, were placed in the dam. Overbroken sections were filled with rock, the outer part being coated with mortar to hold it in place till concrete was placed. Some difficulty was encountered in placing the 6 inch screened gravel beneath the concrete lining on the 1:1 side slopes ahead of the lining operation. Heavy steel plates, located at the plane dividing the concrete and gravel, were finally used. The

gravel was placed behind the plate, keeping the top about 1 foot in advance of the concrete and drawing the plate up with a winch as concrete advanced up the slope.

Concrete was placed in the floor beginning at the bottom of the slope. A heavy jumbo, 30 feet wide, was constructed at the foot of the slope, serving to brace the side walls during the placing of concrete. After stripping the forms, the jumbo was pulled up the slope to the next set-up, using caterpillar tractors located at the intake. The mixer was set up midway of the chute section on the right side of the spillway and then moved to the left side near the axis of the dam to pour the upper portion. Placing equipment consisted of buggies delivering concrete to chutes.

Construction of the parapet and curb walls was begun by Cox & Christiansen, of Provo, Utah, in September 1931, after allowing for settlement of the dam. Excavation for the parapet wall was made by team and hand methods. Concrete aggregates for the walls were shipped from Salt Lake City and all materials were unloaded at the siding at the right abutment of the dam. The form panels were constructed of 4-inch flooring on 2- by 4-inch studs, lined on the inside with Prest Wood. Contraction joints, at approximately 15-foot centers, were provided by inserting a 16-inch steel plate half way down the wall and pulling the plate out before the concrete reached its final set.

A concrete mixer was conveniently located at the crest of the dam and water was pumped from the river at the upper tunnel portal. Forms were stripped from the parapet wall about 12 hours after completing the pour. Exposed surfaces were finished by a wooden float working in a small amount of neat cement, after which the wall was covered with burlap and kept moist for about three days, then rubbed down with a no. 7 carborundum brick to obliterate all form marks. After backfilling about the walls, a suitable roadway surface was made by hauling in and spreading a one inch layer of crushed limestone on the crest.

Concrete aggregates for all other structures at the dam were processed from the river gravel deposits in the river bed below the dam. A bucket delivered the material to a large hopper which delivered the aggregate to shaker screens. A small amount of coal was found in the aggregates, but not in sufficient quantity to seriously affect the concrete strength and durability. To avoid the possibility of erosion due to high water velocities, a finishing coat of sand, shipped from Salt Lake City, was used at the surfaces of the tunnel and spillway floors. The sand from the river bed required washing. A large excess of peagravel of 4 to 5%-inch size was necessarily wasted, after which a fairly well-graded aggregate resulted.

COSTS

The following tabulation shows the quantities and costs for the different features of the work; also the total cost of the dam, including changes and extra work.