52, 259

359

Each lift of concrete on the dam was begun with a layer of grout from one-half to 1 inch in depth, followed by two batches of concrete without cobbles. Repeated layers from 8 to 12 inches thick were then spread until a 4-foot lift was completed. Surfaces of construction joints were broomed with wire brushes before the concrete set.

Concrete placing was begun June 3, 1930, and was completed November 7, 1930. A total of 56,358 cubic yards was placed, of which 55,373 were in the dam and 985 in other parts of the work.

The grouting of radial contraction joints was performed by Government forces from March 3 to 10, 1931. The vertical contraction joints were provided with one or two horizontal 1-inch pipe headers on radial lines and vertical one-half-inch pipe risers three feet apart. The risers were provided with a pair of electrical-conduit box covers eight feet apart vertically. Grouting was done with two duplex slush pumps which were operated by compressed air from a portable compressor of 200-cubic-foot-per-minute capacity. All equipment was operated from the top of the dam. Grout with a water-cement ratio of 1.0 was mixed in twosack batches.

A summary of grouting quantities and costs is given in the following tabulation:

Total joint area, square feet

Number of sacks of cement used

115

0.055

Installing and painting high-pressure control pipe and fittings, oil pump, Ford engine, and oil tank for high

pressure emergency gates.

THE STORAGE SYSTEM of the Yakima project consists of six reservoirs, with a combined storage capacity of 1,039,000 acre-feet, to conserve the surplus winter and flood run-off for subsequent irrigation use on 277,000 acres of land within completed or proposed divisions of the Yakima project, and to supplement the water supply for 120,000 acres within the Wapato Indian Reservation and about 50,000 acres of privately developed lands under Warren Act contracts. Tieton Reservoir supplies about 20 percent of the storage demand.

Tieton Dam, on the Tieton River 30 miles west of Yakima, Wash., is 42 miles from Yakima by road and 26 miles west of Naches, the nearest railroad point. Construction was started in January 1917, but was discontinued in July 1918, on account of the World War. Work was resumed in April 1921, and the dam was completed in April 1925.

RESERVOIR

The reservoir has a volume of 202,500 acre-feet with a 2-foot depth of water passing over the raised spillway drum gates; and 197,000 acre-feet capacity at elevation 2,926.0, the top of the drum gates when raised. At this elevation the reservoir is 9 miles long and has an area of 2,500 acres. The drainage area upstream from the dam is 187 square miles. The average annual run-off over a period of 18 years was 350,000 acre-feet. The reservoir site was heavily timbered and required the clearing of 2,700 acres.

The damsite is at a narrows in Tieton Canyon with a solid rock (andesite) cliff at the west abutment and a more gently sloping mountain side, with an earth cover 30 to 60 feet deep over the bedrock, at the east abutment. The cover in the river section was 92 feet to shale. The spillway and diversion tunnel are located in the rock cliff at the west end of the dam.

THE DAM

Tieton Dam is an earth, gravel, and rock fill embankment, with a concrete corewall extending from bedrock to the crest and anchored in solid rock on both abutments. The height from the deepest corewall foundation to the

crest is 321 feet. The total yardage in the embankment is 1,995,000 cubic yards, of which 1,570,000 are earth and gravel and the remainder rock. The length of the dam along the crest is 905 feet and the thickness from toe to toe is 1,110 feet through the river section. The total quantity of concrete in the various parts of the structure is 43,600 cubic yards.

Six test pits were sunk to bedrock along the axis of the dam in 1917-18, to test the foundation. These disclosed a cover of 20 to 60 feet of earth on the east abutment, overlying andesite bedrock; and 90 feet of compact gravel, clay, and sand for 150 feet across the river bed, overlying compact shale. The andesite was drilled to a depth of 20 to 65 feet; and the river pit was sunk 22 feet into shale and the shale investigated with a diamond drill to a depth of 67 feet. These investigations gave proof of a satisfactory foundation.

On resuming work in 1921 it was decided to excavate the cut-off trench for the corewall through the overburden by mining methods rather than by open cut. The test pits were rigged as working shafts with frames, cages, and hoists. At the bottom of the shafts, drifts were started in either or both directions and the spoil hoisted to the surface. Mine timbering and lagging were installed, and when the bottom drift had progressed a sufficient distance, the top lagging was taken out at convenient points and enough material picked or barred down into waiting cars to permit the placing of timbers. Then this drift was extended and successive drifts opened in a similar manner. As soon as possible the lower drifts were filled with concrete and the corewall built up from the bottom. All drifts were dug into bedrock until solid rock was found, requiring a minimum penetration of 10 feet. The thickness of the wall below ground was 5 feet, with the base widened so that the pressure on the foundation would not exceed 8 tons per square foot. The wall was carried 20 to 30 feet into the shale across the river bed. Five holes were drilled into the rock, and, when grouted, were found so tight that no further grouting of the corewall foundation was necessary.

Plain concrete of 1:22:5 proportions, by volume, was used below ground. The concrete was completed to the ground surface in the river section March 2, 1922. The

corewall above ground varied from 5 feet thick at the ground surface to 1 foot thick at the dam crest, both faces having a batter of 1:100. The wall above ground was heavily reinforced and of the same mix as below ground. Wooden forms were used, and the wall was kept 10 to 40 feet above the pool elevation in the sluice fill. Excavation and concreting in the underground portion of the abutments was kept slightly ahead of the exposed portion. Two 4-foot diameter observation wells were built on the downstream face of the corewall to facilitate future inspection of the corewall and puddle core. The corewall was carried above the top of the embankment to form a parapet 3 feet high. Tieton Dam was designed and built as an earth fill type, using the hydraulic method for separating the fines from the fill material and concentrating them at the upstream side of the corewall and for washing the fines from the material on the downstream side of the corewall. Both

the upstream and downstream slopes are reinforced by rock fills. Watertightness was obtained through the comparatively thin puddle core and the concrete corewall.

The embankment above the corewall was built of earth, gravel, and boulders, excavated from borrow pits by steam and electric shovels, loaded on cars, hauled to the outer edge of the upper slope of the dam and dumped from trestles. Streams of water from hydraulic giants, developing about 85 pounds nozzle pressure, were then directed on the dumped material. This sluicing tended to separate the smaller rocks, sand, and clay and carry them from the dump toward the corewall, leaving the coarsest rocks on the outer slope, well compacted, and the voids filled with smaller rocks and gravel. The suspended material in the water was gradually deposited on a gently sloping beach, extending from the dump to the core pool. The width of the pool was maintained slightly greater than one-third the

distance down from the top of the dam. By the time the sluicing water reached the pool it held in suspension only the finest sand and clay. The fine sand was deposited at the outer edge of the pool, and the clay towards the corewall. Thus was built up a tapering puddle core of impermeable material in front of the corewall.

The height of the water in the pool was regulated through conduits in the west abutment, connected to the diversion tunnel. The coarse material near the trestles washed to a slope of 1+%: 1; the slope to the pool from the edge of the coarse material was 1:10. The top 20 feet was finished with top soil from the river bottom. Large boulders from the borrow pit and rock from the tunnel and spillway were placed as an added layer outside of the coarse sluice fill. The upper 100 feet of the slope was finished off with 4 feet of riprap placed on a 3:1 slope.

The earth embankment material below the corewall was secured from the coarser material in the borrow pit, hauled to the lower side of the corewall at the toe or on the slope

on a 1:1 slope, and dumped from trestles. This material was sluiced in the same way the material upstream of the corewall was treated; but no pool was maintained and the fines were carried off by the water to leave a fill grading from very coarse material at the outer slope through finer rock and gravel to coarse sand at the corewall. This left a heavy, compact, free-draining fill below the corewall. Clean rock from the tunnel and spillway was used to build out the embankment to a 2:1 slope. The top was finished one foot above the proposed height, to allow for settlement, using 18 inches of spillway rock and 6 inches of clean gravel. In constructing the sluiced fills, great care was taken to maintain the corewall in as vertical a position as possible. Readings were taken at least once daily; and the relative heights of the pool above the wall, and the fill below, were maintained to keep the wall nearly vertical. Especial care was taken to prevent permanent movement downstream. The maximum movement in any one day was 0.03 of a foot, and the maximum for any one point during the time of