Page images
PDF
EPUB
[graphic]

Figure 265.-View looking east along downstream face of dam, showing penstock pipes protruding from face of dam. Penstock support is at right foreground. P557-420-6001, May 19, 1961.

until a number of blocks got close to their ultimate height. Block 2 was topped out at elevation 3715.0 on March 30, 1963. Blocks 4 and 6 followed on April 10 and 19, respectively. Beginning with block 20 on May 8, other blocks were topped out at about 7-day intervals. The last two lifts from elevation 3705.0 to elevation 3710.0 and from elevation 3710.0 to elevation 3715.0 were 5-foot lifts. Block 25, the last block to be completed, was topped out at elevation 3715.0 on September 13, 1963. Placement of mass concrete in the dam took slightly more than 3 years, with the first placement being made on June 17, 1960, and the last placement on September 13, 1963.

Figure 266 shows the upstream face of the dam as of July 25, 1963.

2. Structural Behavior Installations

176. REFERENCE. Chapter IV presents a discussion on the structural behavior testing apparatus that is used in the dam. These are briefly described below.

177. EMBEDDED INSTRUMENTS. The embedded instruments include resistance thermometers for measuring the temperature of the concrete in the dam, strain meters for measuring the conditions of strain in the concrete, stress meters for measuring the stress in the concrete, joint meters for measuring the opening of the contraction joints, and deformation meters for for measuring the deformation of the foundation and abutment rock. These instruments

[graphic]

Figure 266.-Upstream face of Glen Canyon Dam during construction as seen from the footbridge. P557-420-8625, July 25, 1963.

were installed in the dam as shown on the drawings. All of the meters were furnished by the Government and installed by the prime contractor. These instruments are of the elastic-wire type with the exception of the resistance-wire type thermometers. Embedded in the mass concrete of the dam, the instruments are connected by electrical cables to terminal boards located in the galleries of the dam where systematic readings are made with portable wheatstone bridges.

The several systems of 1,658 embedded instruments include 1,142 strain meters, 60 stress meters, 74 resistance thermometers, 264 joint meters, and 112 deformation meters.

All instruments are embedded in the mass concrete of the dam and are connected to convenient terminal boards by three or four conductor electrical cables. The cables are rubber jacketed, rubber insulated, No.

16 A.W.G., stranded, and of matched resistance. The terminal boards and outlet boxes are located in the galleries of the dam where readings are made using specially built, portable, wheatstone-bridge test sets. A total of 74 terminal boards were used; eleven 10-terminal boards, four 12-terminal, seventeen 20-terminal, twenty-two 25-terminal, and twenty 30-terminal boards. In addition, 116 outlet boxes were used for terminating meter cables in the dam. Two types of test sets are used, a wheatstone-bridge test set and a strain meter test set, which is a specially built wheatstone bridge. Padded carrying cases are used to protect the test sets.

Strain meters are installed in clusters of 12 instruments each at several points on radial lines that define section of arches and cantilevers in the dam, forming the major system of instruments. The radial lines of strain meter clusters are located near the base

of the maximum dam section and in three arches, uniformly spaced between the base of the dam and about two-thirds of the elevation of the dam. In each arch, the lines of instrument clusters are in the maximum section, near each abutment and at applicable intermediate locations between the abutments and the maximum section. The lowest arch contains three lines of instruments, the second contains five lines of instruments, and the third arch contains seven lines of instruments. Two arches between the two-thirds elevation of the dam and the top of the dam are instrumented using series of stress meters installed on seven radial lines in each arch. These instruments determine stress only in the direction of arch thrust. Pairs of strain meters are installed under free-surface metal canister-like covers, one pair of meters with each elevation of instruments, to detect possible autogenous growth or shrinkage of the mass concrete. At three widely separated locations near the top of the dam, trios of three-dimensionally arranged strain meters are installed near the upstream and downstream faces of the dam to determine surface stress in the structure.

In conjunction with the installation of strain meters and stress meters throughout the dam, joint meters were placed on the radial contraction joints at the same elevations as the meter clusters. Where the dam's longitudinal joint crosses blocks containing strain meters or stress meters, joint meters were installed on the longitudinal joint near its intersection with the radial joints. Additional joint meters were installed on the longitudinal joint at intermediate elevations between arches containing the strain meters and stress meters. Patterns of joint meters were installed on each of the two radial joints nearest each dam abutment and in the upper 200 feet of the dam elevation. The joint meters were embedded so that they were bisected by the transverse or longitudinal contraction joints and were properly anchored.

An installation of three mutually perpendicular meters-two strain meters and one joint meter-is located in the control cable tunnel where a stress relief joint in the abutment rock, termed the A joint, crosses the tunnel to detect movement of the joint. Electrical cables from the meters extend to three outlet boxes located in the powerplant.

Deformation meters were installed to detect initial foundation deformation as the load is applied to the sandstone foundation, and the elastic deformation of the foundation after the initial deformation has stopped. The deformation meters were installed so that they were bisected by the plane of contact between the

[blocks in formation]

Initially, the contractor tried a blockout procedure for meter group installation. However, this was rejected early for economic reasons and the meter groups were most efficiently installed in excavations in the fresh concrete. As the clusters were assembled on a metal template, or spider, installation was quickly made by leveling and plumbing a horizontal and vertical meter of the cluster. Cable trenches were excavated in the fresh concrete to provide for a minimum coverage of 6 inches. The cables were laid in the trenches and the trenches back filled by hand. The locations of the buried cables and meters were marked with an iron oxide dust, which was worked into the concrete surface, to minimize damage to the installation by drilling of holes for form installations and other purposes. Meter outlet boxes were installed at the terminal points directly upon the forms, and the terminal boards and covers were installed later when the terminals were soldered. When terminal boards were below the meter installation, conduit was usually installed for routing the cable from the meters to the boards.

As individual unit pay items were provided for these installations, no unusual difficulties were experienced in minor changes in the quantity of items. Some difficulties occasionally occurred when inexperienced workmen were assigned to the meter installation work. The most efficient and best installations were made when a single experienced crew was responsible for the meter installation.

179. DEFLECTION MEASUREMENTS. in addition to the embedded instrument installations, two systems of measurements employing refined methods of surveying were provided for determining the manner in which the dam deflects during periods of reservoir filling and operation.

One system comprises five plumblines, each in a formed well (fig. 267) extending from the top of the dam to a point near the foundation. The wells are located in the maximum section and at points approximately one-third and two-thirds the distances between the maximum section and the abutments. The plumblines are located in blocks 4, 7, 12, 18 and 21 of the dam, and have a total of 19 reading stations. At each reading station, movement between the dam and plumbline is measured using a micrometer slide and microscope apparatus. The micrometer can be read in ten-thousandths of an inch. The reading stations are oriented in plan so that measurements of deformation are in planes which are radial and tangential to the dam's axis. By this expedient, the measurements require no trigonometric resolution to obtain deformation in the desired directions. Readings are

Figure 267.-Plumbline well reading station in block 4 of dam at elevation 3390.00. P557-420-9334, February 7, 1964.

made periodically and are tabulated on forms in a manner that computer card punching can be made directly from the data sheet without further transposition. or trigonometric resolution. The second system for determining deflection of the dam consists of a grid system of 68 targets placed on the downstream face of the dam and 17 targets on the foundation along the abutments. Locations of the targets are charted periodically from primary theodolite stations on each abutment downstream of the dam and from secondary stations on the canyon rim, using precise triangulation surveying methods. This system is discussed in further detail under section 186 on surveys.

180. UPLIFT PRESSURE PIPES. Hydrostatic uplift at the base of the dam is measured at 41 locations by pipes connecting to wells at the concrete-rock contact plane and terminating in the dam galleries. Located in blocks 2, 4, 5, 7, 11, 16, 19 and 25, the pipes are arranged in seven lines, each line being made up of from five to seven pipes. Permanent data showing the elevation at which the pipes are installed are recorded on data sheets and readings are made at appropriate intervals. Pressure is measured by means of a Bourdon-type pressure gage calibrated in feet of water, attached through a gage cock to the uplift pipe. When zero pressure is indicated in a pipe, the water level is determined by sounding. Continued zero pressure with water standing at the level of the pipe is investigated further by adding a transparent standpipe section to the pipe to observe the level to which the water rises.

[merged small][graphic][merged small][merged small][merged small][merged small]

182. SEISMOGRAPH STATION. A seismograph station, located approximately 11 miles northwest of the damsite, records earthquake shocks. Records from the station show the magnitude of any earthquake

[merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors]
[merged small][ocr errors][ocr errors][merged small][ocr errors][ocr errors]

DAM, POWERPLANT, AND APPURTENANT STRUCTURES

tremors in the vicinity and also serve to determine any possible change in local seismic activity that may occur in the area due to the increased weight of the reservoir. The equipment from the Bureau's Hungry Horse project was initially installed, but was replaced by new equipment in September 1964 when replacement parts for the obsolete equipment could no longer be obtained. Installation was made by members of the U.S. Coast and Geodetic Survey who also trained Bureau personnel in operation of the station.

The seismograph vault was constructed under specifications No. DC-5163 by W. W. Clyde and Co. of Springville, Utah, in the summer of 1959. The vault is 10 by 22 feet with reinforced concrete floor, walls, roof, retaining walls, and instrument piers. The walls and roof were 9 inches thick, the floor was 4 inches thick and the retaining wing walls ranged from 9 to 6 inches in thickness. The roof sloped 2 feet in 22 feet toward the open end of the vault. Backfill was placed around three sides and over the roof. A complete electrical system was installed by the contractor and electric power was supplied by Arizona Public Service Co. over a line which they constructed.

Approximately 2 miles of 12-foot-wide unsurfaced road was constructed under specifications No. DC-5163 to provide access from U.S. Highway No. 89 to the vault.

3. Concrete Cooling and Grouting

183. CONCRETE COOLING. Initial cooling of the mass concrete in the dam was provided to remove the heat of hydration. This was accomplished by circulating chilled water for a period of 12 days through 1-inch aluminum tubing, placed on top of each 7.5-foot lift (fig. 63). Secondary cooling to shrink the blocks prior to grouting continued for about 40 days or until a temperature of 40° F. was reached in concrete below elevation 3450 and 50° F. in concrete for elevation 3450 to the top of the dam.

first

Cooling water came from a package refrigeration unit located just downstream of block 11, with a similar unit being used to cool the mass concrete in the machine shop and service bays. This package unit was used to cool concrete in the dam until August 3, 1960, and then a chiller, supplied with liquid ammonia from the main refrigeration plant, was used.

Between January and April 1961, six chillers were installed to supply additional cooling water. Three chillers were installed upstream of unit bay 1 of the powerplant and were connected to 8-inch headers

installed on brackets above the elevation 3120 catwalk across the downstream face of the dam. The fourth chiller supplied cooling water for concrete in the machine shop, the service bay, and the dam above elevation 3060. Two chillers were placed on the elevation 3180 catwalk for initial cooling above elevation 3180 while the other cooling system was used for secondary cooling of the elevation 3120 grout lift.

In January 1962, three chillers were moved to the downstream end of the refrigeration plant on the elevation 3715 bench. Gravity flow of cooling water through the cooling coils was used for both initial and secondary cooling. Pressure was reduced by valves located on the elevation 3240 catwalk on the downstream face of block 21. Two pumps, rated at 1,800 gallons per minute at 392 feet of head, were installed on the elevation 3240 catwalk to pump the water back to the chillers.

Pressure-reducing valves and return pumps were also installed on the elevation 3300 catwalk on the face of block 22 for initial cooling. These pumping stations were raised to higher stations as necessary. The cooling water was delivered through 8-inch horizontal headers installed across the face of the dam. Vertical 4-inch headers led from the 8-inch header to blocks being cooled, and 1-1/2-inch headers led from there to the 1-inch aluminum cooling pipe. As the blocks became small, near the top of the dam, the flow of cooling water had to be reduced below 4 gallons per minute to per keep the lifts from cooling faster than 1-1/2° F. day. Cooling water normally flowed at the rate of 4 gallons per minute, except during some cold periods when the rate of flow was increased to prevent freezing.

STRESSES DURING 184. UNUSUAL CONSTRUCTION. Numerous horizontal and vertical cracks appeared in the dam blocks beginning in 1960. These cracks appeared especially during final cooling and grouting. They were plugged with lead wool before grouting of a grout lift and sealed by the contraction joint grouting. A number of cracks showed up in block 8-B. Two mats of reinforcing steel were placed in the elevation 3112.5 lift to stop a crack which extended from the 8-B-9-B block line at elevation 3067.5 and from the 7-B-8-B block line at elevation 3075 extending to the top and across the surface of the elevation 3097.5 lift and to the top of the elevation 3105 lift. The crack was not noted higher than elevation 3105.

It was thought that changing the intensity or pattern of the temperature stresses within each block by reducing the temperature gradient might be a solution to avoid this cracking. The cooling procedure

« PreviousContinue »