high temperatures were probably due in part, if not entirely, to above normal, and near record, air and water temperatures. Air temperatures at the damsite were approximately 10° higher and water temperatures about 5° higher than recorded normal temperatures.

(c) Initial Cooling--1962. --Placement of mass concrete was resumed on April 2, 1962, and was completed November 15, 1962. During that period, approximately 517,000 cubic yards of mass concrete were placed. The initial cooling procedures used in 1962 were essentially the same as the previous year except that no coarse aggregate sprinkling was performed. The average cooling water temperature ranged from a low of 50° F. in April to a high of 70° F. in July. The cooling water temperatures at the supply end of the coils were generally about 2° F. higher than the temperature of river water due to the length of exposed supply lines and risers. Average placing temperature during the summer months was about 67° F., and the average maximum temperature was approximately 93° F. Maximum temperatures in some blocks during the summer months were as high as 102° F. The maximum temperatures as recorded were taken midway in the concrete lifts. Owing to the temperature distribution in a 7-1/2-foot lift, a temperature of 100° F. at midlift would indicate a mean temperature in that lift of approximately 88° F. Similarly, the average maximum temperature of 93° F. would indicate a mean maximum temperature of approximately 81° F.

The 3-1/2-foot cooling pipe spacing on concrete which was started in 1961 was maintained to elevation 5820, where 5-foot spacing was resumed. This reduced spacing was maintained when it was thought that reservoir filling progress might require cooling and grouting of the elevation 5760-5820 grout lift late in the fall of 1962. Spacing was reduced to 4 feet in September 1962 as each block reached elevation 6007.5. This reduced spacing was required when all concrete placed above that elevation consisted of the rich exterior face mix, which contained no pozzolan and more cement than the interior mass concrete mix.

During the fall, initial cooling was performed with a flow through each coil of from 6 to 8 gallons per minute for about 7 days, which was then reduced to about 4 gallons per minute for the remainder of the 12-day period. In October and November, the initial cooling period was reduced to less than 12 days in some blocks. The combination of colder air temperatures and exposed narrow blocks near the top of the dam resulted in rapid temperature drops to the point where little or no cooling was required in some blocks after the concrete had reached its peak temperature. The initial cooling program was ended on November 20, 1962.

203. Final Cooling Procedures. Final cooling of mass concrete in the dam was performed during the winter months. This was necessary in order to provide river water of a low enough temperature to obtain the desired concrete temperatures. Characteristics of mass concrete are adversely affected when temperatures are lowered to or below the placing temperatures within 2 months after placement. For that reason, a delay or time lag was maintained between initial and final cooling.

The specifications provided for cooling mass concrete to a temperature of 38° F. Owing to the higher than anticipated peak temperatures, this would have required a temperature reduction of from 45° to 60° F. This amount of cooling would probably have resulted in cracking of the abutment blocks due to the restraining effects of the foundation rock. In accordance with recommendations of the Board of Consultants dated October 16, 1961, a trial load analysis was performed using a 38° F. cooling zone in the main portion of the dam, a 50° F. cooling zone in all abutment blocks, and a 45° F. transition cooling zone between the 50° and 38° F. zones. The cooling program resulting from the trial load analysis was outlined as shown in the following tabulation:

The above cooling schedule was generally adhered to; however, requirements were relaxed in some areas when it became evident during final cooling in 1963 that desired temperatures could not be obtained with the available cooling water supply.

(c) Final Cooling--1961-1962. --The first season of final cooling was started in October 1961 and was continued until March 29, 1962. All concrete up to elevation 5760, approximately 407,000 cubic yards, was cooled to the desired temperatures.

The specifications provided that concrete could not be placed in walls and floors of the powerplant structure until contraction joints in the dam were grouted to elevation 5640, and similarly that walls and floors of the river outlet structure could not be placed until joints were grouted to elevation 5700. The contractor had set up his work schedules and plant for winter placing operations in these areas, and it became necessary to have the concrete cooled and joints grouted during the winter months to avoid a delay in placing powerplant concrete. General practice in other Bureau dams has been to cool during the winter months and to grout contraction joints early in the spring when there is no possibility of the concrete being at temperatures below 32° F. Special instructions from the

Denver office granted permission to grout those joints below elevation 5640 which affected powerplant construction if the depth of frozen concrete did not exceed 5 feet. These instructions also provided that other joints including the separate upstream grout systems below elevation 5640 could be grouted if temperature measurements indicated a depth of frozen concrete of less than 15 inches. The upstream face of the dam was covered with muck and 50° F. spring water to approximately elevation 5605, and there was no problem of frozen concrete below that elevation.

Temperature measurements were taken at several locations on the upstream and downstream faces of the dam, and depths of frozen concrete were considerably less than outlined above. Grouting of contraction joints in this area was performed as soon as the concrete was cooled to the required temperatures.

In order to place the diversion tunnel plug in the fall of 1962, it was necessary to grout contraction joints to the level of the river outlets at elevation 5743. Although the specifications required one full 60-foot grout lift of concrete to be placed above the elevation to which joints were to be grouted, this requirement was relaxed to allow grouting to elevation 5760 provided that the minimum concrete level in all low blocks was at elevation 5767.5.

All cooling during the 1961-1962 season was accomplished with river water as the coolant. The contractor had originally planned to use river water to bring concrete temperatures down to 50° F. or 60° F. and then to switch to a calcium chloride brine system during the colder months for final cooling. As the season progressed, the contractor decided not to use the brine system but rather to continue cooling with river water which averaged approximately 33° F. for the rest of the season. Considerable difficulty was experienced with frozen headers, valves, and hoses, and a three- or four-man pipefitter crew was required to maintain the system.

(d) Final Cooling--1962-1963. --Final cooling of all concrete from elevation 5760 to the top of the dam was completed during this season. Although final cooling for part of the elevation 5820-5880 grout lift was started for 1 day on September 16, there was not enough cooling system capacity to handle both final cooling and the initial cooling which was in progress at higher elevations. On October 11, 1962, final cooling was again started and was continued until completion of the cooling program on April 18, 1963.

The general plan of cooling during this season was to cool areas with high temperatures for a short time and bring them down to a temperature more nearly equal to other grout lifts, and then to cool one grout lift at a time to final temperature. This procedure helped to eliminate long continuous periods of final cooling and resulting large temperature drops. At the higher elevations which were cooled during this season, only one grout lift could be cooled at a time because of the pump capacity. Depending on the elevations being cooled, the contractor's pumps supplied from 2,500 to 3,000 gallons per minute to the cooling coils.

When secondary cooling was started in October, the cooling water was being pumped from a pond of waste water between the dam and the downstream cofferdam. The temperature of this water averaged about 60° F. while that in the river was approximately 48° F. In November the downstream cofferdam was removed and the average temperature of the supply water was 44° F. while the river water averaged 40° F. This 4° F. difference in the river water and the cooling water supply was partly due to the long exposed supply lines, and partly due to the close proximity of the pump intake and the waste water discharge. During the last part of November the intake and discharge lines were separated. It should be noted that in November the river water, which was drawn from the reservoir through the outlet tubes, had an average temperature of 40° F. and during the same period of the previous year the river water average temperature was about 33° F. River water temperatures stayed higher than the previous year throughout the winter, dropping to about 38° F. in December and early January and then to about 34° F. or 35° F. for most of the remainder of the final cooling program. The possibility of obtaining colder water from the reservoir surface was considered, but was discarded when subsequent measurements showed that water temperatures at depths of 3, 10, 15, and 20 feet at distances ranging up to 1, 000 feet upstream from the dam were generally within 1° F. or 2° F. of water discharged through the outlet tubes and into the tailrace.

Because of the difficulties experienced during the previous season with frozen valves and headers, the contractor's brine system was put into operation December 21, 1962. In order to convert to the closed brine system, a surge tank and a heat exchanger were added to the already operating water cooling system. Brine was mixed in the 10,000gallon surge tank located on the left abutment at approximately elevation 5900, taken by gravity flow through the heat exchanger located just downstream of the river outlet tubes, pumped through the supply lines to the cooling coils and discharged from the coils through the return lines back into the surge tank. The brine coolant was a 21 percent solution of calcium chloride in water, with a PH of 7.0 and a 1.2 specific gravity. The solution was made with 2.75 pounds of chemically pure calcium chloride and 0.5 percent sodium chromate corrosion inhibitor additive per gallon of solution. Approximately 25,000 gallons of brine were used in the system. Close control of the solution PH was maintained to prevent chemical attack of the aluminum cooling coils by the brine. Because of losses from broken hoses and other leaks, the actual brine solution pumped through the coils was generally considerably weaker than indicated above even though additional calcium chloride and water were added to the storage tank regularly. The heat exchanger consisted of a bundle of 1-inch-outside-diameter cooling pipes in a long metal tank. The brine was pumped through the coils, which had a total surface area of about 4,000 square feet; river water was pumped into one end of the tank at a rate of about 6, 500 gallons per minute, through a series of flow baffles, and discharged back into the river at the other end of the tank. After much experimenting with this exchanger, it was found that the most efficient operation was obtained with a brine flow of about 1,300 gallons per minute. With this rate of flow, the brine temperature was reduced to about 40° F. by river water at 35° F. The capacity of this system was inadequate to meet cooling requirements, and use of the brine system was discontinued about the second week of February 1963. All cooling after that time was completed with river water as the coolant.

Because of the slow progress made in cooling the elevation 5760-5820 grout lift, temperature requirements in the interior portion of the dam were changed in December from 38° to 40° F. These requirements were further modified in January to 42° F. for the elevation 5760-5820 lift only. Final cooling of all concrete to these modified requirements was completed on April 18, 1963.

204. Warming Concrete. The specifications required that the top lift of concrete in blocks which were left exposed over a winter season be warmed up to a temperature of not less than 50° F. as measured at a point 4 feet below the surface of the exposed block before new concrete could be placed. It was further specified that this warming was to be accomplished by circulating water with a temperature of not more than 100° F. through the top two embedded cooling coils of each block. These provisions were made to minimize cracking on the exposed horizontal construction joints.

Attempts in the early spring of 1961 to warm the tops of five blocks using unheated spring water at 50° F., and then the same water heated by gas burners to about 60° F., were unsuccessful. Finally, an old threshing machine-type steam boiler was installed using the 50° F. spring water as a water supply. This boiler supplied water at 90° to 95° F. to the cooling coils, and raised concrete temperatures approximately 1° F. per day. Two weeks of this operation raised concrete temperatures to a range of from 50° to 55° F.

On March 1, 1962, the contractor attempted to circulate 100° F. water from the boiler through the top lifts of 16 blocks placed in 1961. All of the cooling coils but one in block 6 were found to be frozen. The coils were frozen at both the upstream and downstream faces of the dam and along the sides of some of the exposed high blocks. An unsuccessful attempt was made to thaw the frozen coils by inserting a small rubber or plastic steam hose into the coils. In another attempt, electrical current from a welding machine was applied to the coils; but a circuit could not be completed, probably because of rubber gaskets in the cooling pipe couplings. Finally on March 25, thawing the coils with an electrical current from a portable 480-volt transformer was successful. Most of the coils were thawed and were circulating warm water by March 26. After the first few days, water was supplied to the coils at an average temperature of about 95° F. and returned to the boiler at about 85° F. Concrete warming operations were completed in all blocks by April 9, 1962.

205. Aggregate Sprinkling. In accordance with recommendations made by the Board of Consultants in its report dated October 23, 1958, the contractor was directed to install

sprinkling systems for coarse aggregate in both the aggregate plant stockpiles, and the batching plant surge piles. The installation at each location was to include necessary pumps, sprinklers, drains, etc. to provide a water sprinkling capacity of 160 gallons per minute (40 gallons per minute for each coarse aggregate gradation). Since no provision was made for sprinkling and evaporative cooling of aggregates in the specifications, payment for the installation and operation of these sprinkler systems was included in an order for changes.

The original intent was for intermittent sprinkling of aggregate stockpiles for placement in any lift of which any part was within 15 feet of rock, and when placing temperatures were at or exceeded 60° F. Sprinkling was performed as outlined above during the 1961 placing season until about mid-June. In June, after concrete placing temperatures had reached as high as 73° F., instructions were received from the Denver office to extend aggregate sprinkling to all mass concrete placed in the dam during the months of July, August, and September. When concrete temperatures continued at high levels throughout June and July, a representative from the Denver office visited the project, consulted with project personnel, and made recommendations for changes in operation of the aggregate sprinkling systems. During the month of August, a concerted effort was made to obtain the most efficient methods of operating the sprinkler systems. Several combinations of methods including both intermittent and continuous sprinkling and fog spraying at either or both the aggregate plant and batching plant were tried. No observable reduction in placing temperatures resulted from any of the sprinkling methods used, and temperatures were not noticeably higher when no sprinkling was performed.

In its report of October 16, 1961, the Board of Consultants made the following remarks concerning the aggregate sprinkling: "Due to cooling during the processing operation, followed by the evaporation of moisture in the stockpiles, the temperatures of the aggregates in stockpiles are naturally as low as can be obtained by evaporation and any extra water spraying does no good. During periods of hot weather observations reveal that temperatures of aggregate in stockpiles are usually somewhat less than the temperatures of river water.

Operation of the sprinkling systems was discontinued after August 1961 and was not resumed for the 1962 placing season.

206. Diversion Tunnel Plug Cooling. Between December 18, 1962, and January 3, 1963, 1, 215 cubic yards of concrete were placed in three lifts in the diversion tunnel plug. Cooling water for the plug was obtained from reservoir leakage into the tunnel upstream from the plug and was pumped through approximately 2,900 lineal feet of cooling pipe embedded in the plug. The concrete temperature in the plug was reduced to within 5° F. of the cooling water, and on January 23, 1963, the contraction joint between the plug and the tunnel lining was grouted.

207. Concrete Cracking. At the end of the 1960 placing season, cracks were observed in the mass concrete of several high blocks. The most serious was a crack in block 16 which extended completely across the block in the first two lifts above an abrupt irregularity in the foundation rock. During the winter, hairline cracks were observed in other blocks. Before concrete placing was resumed in the spring of 1961, two members of the Denver office visited the project to inspect the cracks and discuss remedial measures. They found that most of the hairline cracks had closed during the winter due to the effectiveness of the protective coverings placed over and around the exposed foundation gallery. Instructions were given to place a double mat of reinforcement over the crack in block 16, and to calk a horizontal leafing crack which occurred along the 15-16 joint at elevation 5580 and extended past the metal seals and across the upstream face of block 16.

During the 1961 placing season, cracks developed in the surface of block 15 at elevation 5625 between the elevator shaft and the 15-16 contraction joint and also in the same block and elevation between the elevator shaft and the penstock. Corrective steel was placed over both cracks at elevation 5625 and again at elevation 5632.5.

Again in April 1962, a representative from the Denver office inspected concrete cracking from the 1961 placing season before placing was resumed. During this inspection, no serious structural cracking was found. All of the cracks were described as hairline cracks, and occurred with one exception in high blocks. As a result of this inspection, reinforcement mats were placed to straddle cracks in blocks 10, 12, 13, 14 and 16.