drawn by a standard gage, 8-ton gas locomotive to the cableway loading dock at the dam, 1,500 feet distant. Under normal operations one load was delivered every 4 minutes. The concrete was chuted into place or delivered by gravity in an 8-cubic yard bottom dump cableway bucket, and spaded or puddled into place by workmen. Concrete next to the forms was spaded lightly to produce smooth surfaces.

Before placing concrete, the foundation rock was cleaned of all mud, excess water, and debris, and all splattered grout and rock scale removed by sand blasting. The time elapsing between completion of a pour and beginning of cleanup varied from 6 hours on hot days to 24 hours on cool nights. As soon as the part of the pour that had been placed first became hard enough, the soft laitance was removed by wire brushing. Exposed rock surfaces were hand blasted before concreting.

A system of wooden panel forms, 4 feet high by 8 feet long, was used to confine the concrete to 4-foot lifts in panel blocks

bounded by the contraction joints and the upstream and downstream faces of the dam. As soon as the irregularities of the bed rock were covered, a regular schedule of 4-foot lifts was started. The rate of placing was limited to not more than 4 feet in 72 hours, and not more then 28 feet in 30 days, except in panels 3 and 4, which were left at elevation 2,361 to provide landing platforms for the cableway bucket.

All horizontal concrete surfaces and foundation rock of the dam to which new concrete adhered was covered with a layer of mortar, mixed in proportion of 1 part cement and 2 parts sand. Following this, a wet mix, without cobbles, was placed to a depth of about 6 inches, forming a cushion to receive the regular cobble mix. Special care was taken to prevent the accumulation of excess grout around the copper seals and corners of the panels by keeping the concrete at these points higher than the remaining lift. All lifts were started at the downstream face to insure proper union with subsequent work. In the lower levels of the dam, the lifts were placed in successive horizontal layers, step fashion. Horizontal keys were formed by shoveling fresh concrete between 1- by 10-inch boards, held to shape by %-inch iron rod brackets.

During cold weather, aggregates and mixing water were steam heated at the mixers, so that no concrete reached the forms at a temperature lower than 50° F. The fresh concrete at the forms was covered with canvas and protected at this temperature or higher for 72 hours by heating with coke burning salamanders. Cold weather prevented placing during a part of each winter and retarded progress during the fall and spring.

Except in freezing weather, the upstream and downstream surfaces were kept moist by a continual spray of water. The concrete surfaces of the contraction joints were coated with water-gas tar soon after the forms were removed. The horizontal construction joints were wet down as soon as the laitance was removed and kept continually moist until covered with a subsequent lift, or until cured at least 2 weeks. The roadway and top of the parapets were covered with a layer of sand to hold the moisture and to protect the concrete. Concrete in the semicylindrical trashrack structures was placed monolithic with the dam.

SPILLWAY CREST STRUCTURE

The excavation for the spillway crest structure was done with a 1-yard gasoline dragline during November and December 1928. A wooden bulkhead, built in the 5- by 8-foot shaft about 5 feet below the required depth of excavation, kept debris out of the shaft. Broken rock was loaded on trucks and hauled upstream to a spoil bank at the edge of the bluff.

Each form for the spillway crest structure was built at the carpenter shop in one piece and cut in sections for transpor

tation and installation and to accommodate the concrete pours. The control chamber, pier, and bridge forms were built in place. Special grade, - by 4-inch shiplap was used to face the forms.

With the reinforcement steel in place, concrete was placed between construction joints. Most of the revetment lining was hand placed and screeded to conform to the specified shapes. The needle valves, drain, and vent pipes and miscellaneous metal work were embedded in the concrete as the placing progressed. A concrete mix of 1:1.55:3.56, with an average slump of 4 inches at the forms, was placed with the same equipment used in placing the shaft lining.

The foundation rock beneath the control chamber pier was grouted before the revetment paving was placed, whereas the foundation rock beneath the crest structure was grouted after the shaft lining had been grouted. Altogether, 300 sacks of cement grout with a water-cement ratio of 1:0 were forced into 24 grout connections in the foundation rock of the spillway-crest structure and control chamber, under 100 pounds pressure per square inch.

TUNNEL PLUG

Construction of the permanent concrete plug in the diversion and spillway tunnel, upstream from the spillway shaft, was begun on August 30 and completed, except for grouting, on September 16, 1932.

As a preliminary step to diverting the low summer flow of about 130 second-feet through the sluice gates, a wooden gate, 16 inches thick, 36 feet wide, and 30 feet high, was built in the concrete slot at the inlet portal of the diversion tunnel, being suspended from an overhead framework by a steel cable which was burned through, permitting the weighted gate to drop down the greased slot until it keyed into the slot across the bottom. Hay, sawdust, and other material, thrown into the water, effectively sealed the cut-off.

Preparatory to placing the concrete, the trestle, leading from the railroad to the tunnel outlet, was rehabilitated and extended into the tunnel where tracks were laid along the floor.

Placing of concrete was begun after the annual recesses for the plug and all other surfaces with which the concrete would come in contact had been cleaned and chipped to a depth of about 1 inch. Pours were made in 4-foot lifts, grout pipe being carried to contacts for grouting after shrinkage. An 8-inch pipe, through the plug, prevented accumulation of water against the upstream face during construction and was later grouted.

COSTS

The following tabulation indicates the quantities and costs involved in the construction of the dam and appurtenant works to September 30, 1936.