to the main tunnel gate structure, then up through the gate shaft to elevation 5879. 0, the bottom of the 20-inch floatwell pipe. At the top of the 20-inch floatwell pipe, elevation 6104.0, a reservoir level recorder was installed with a system of floats and a selfrecording chart to continuously record the elevation of the reservoir.

154. Trashracks. The trashrack metalwork was manufactured and delivered to the jobsite by the Mountain States Steel Co., of Provo, Utah, under a purchase order issued by the prime contractor. Following receipt on the jobsite, the steel was sandblasted, primed, and hot dipped in coal-tar enamel heated to 390° F. by subcontractor D. E. Burgess Co., of San Francisco, Calif. Assembly in place was accomplished after completion of the main intake structure concreting during the months of January through March 1961.

CHAPTER IX. Construct ion- -INSTALLATION OF TEST APPARATUS

155. General. The test apparatus installed in Navajo Dam consists of a piezometer system with 52 piezometer tips, 2 crossarm settlement installations, and 43 surface settlement points. Figure 12 shows the location and general plan for the test apparatus installation. The test apparatus was installed by the prime contractor under specifications No. DC-5056.

156. Installation of Piezometer Tips. The piezometer system is comprised of twintube piezometer tips, connecting 5/16-inch-outside-diameter plastic tubing, Bourdon-tubetype pressure gages, accessory valves, air trip, water supply, water filter, and pump. Pore-water pressures are transmitted from the piezometer tip through the water-filled tubes and are observed on Bourdon-tube gages mounted in the terminal well. Each piezometer circuit is independent.

The installation consists of 52 twin-tube piezometers, 40 of which are embankment type and 12 foundation type. Details of both types are shown on figure 13.

(a) Foundation Tips.—The 12 foundation tips were placed in the foundation of the dam by drilling holes with a churn drill. The tips located near the surface of the bedrock were placed in 1/4-inch-thick, 6-1/2-inch-inside-diameter casings which had perforations in the lower 18 inches. Tips 1 through 6, which extended into bedrock, were cased only to bedrock. Casings were left in position in all holes.

The piezometer tips were installed by filling the lower 12 inches of the hole with a clean, well-graded, saturated sand; placing the sand-encased tip assembly in the hole; then backfilling with an additional 12 inches of clean, well-graded saturated sand, followed by clay slurry in short increments to the top of the hole. The connecting tubing was then laid in the previously excavated trench to the terminal well. At the same time, the tubing for embankment-type piezometer tips was placed in the trench leading from the terminal well to a vertical riser located 180 feet downstream from the dam centerline of station 40+00.

(b) Embankment Tips.--The 40 embankment-type piezometer tips were installed at station 40+00 (fig. 103) at the locations and elevations shown on figure 12. When the dam embankment reached an elevation approximately 2 feet above the proposed elevations of the embankment-type piezometers, a trench was dug in the embankment with a backhoe and fine graded by hand. The piezometer tips were then placed in hand-excavated offset trenches. The trench was backfilled and hand tamped with impervious material to a minimum depth of 18 inches over the tubing before permitting heavy equipment to pass over the trench. In the zone 1 embankment, bentonite cutoffs were placed at approximately 50-foot intervals. In the zone 2 embankment, bentonite cutoffs were placed approximately 10 feet downstream from each tip location. The risers for embankment piezometer tips above elevation 5750 were installed by using a slip-form. The slip-form riser consisted of a heavy-gage, 24-inch-diameter, 6-foot-long section of pipe with a rack mounted on the top to accommodate the spools of tubing. The exterior compacted backfill was placed to within 2 feet of the top of the form, then the form was raised in 2-foot increments. Raising of the form was readily accomplished by the use of two 5-ton hydraulic jacks. Interior compaction of backfill was maintained to the bottom of the slip-form. Bentonite plugs were installed in the bottom and the top of each riser. Additional plugs were installed at 30-foot intervals along the risers.

Record tests of soil properties were taken at all embankment tip locations and at the foundation tip holes. Tests performed on each sample included mechanical analysis, specific gravity, liquid and plastic limits, and percolation-settlement. The test results are included in appendix B to the final embankment construction report. 1/ A discussion of some pore-pressure observations is given in section 22.

157. Description of Piezometer Tips and Tubing. The piezometer tips (fig. 13) consist of 7/8-inch-diameter by 1/4-inch-thick porous disks sealed in clear plastic. Two 12-inch long by 5/16-inch-outside-diameter plastic tubes are connected to either side of the tips. The joints were tested with an air pressure of 50 pounds per square inch before installation. The tubing connecting the piezometer tips to the terminal well is 5/16-inchoutside-diameter clear plastic tubing. All connections were made with compression-type fittings.

1/"Final Construction Report, Navajo Dam--Appendix A, Final Embankment Construction Report, " Colorado River Storage Project, Bureau of Reclamation, 1963 (unpublished).

Tubing from the 52 piezometer tips was brought into the terminal well through a 6-inch pipe in the upstream wall. A 3-foot-long plug of grout was placed around the piezometer tubes where they entered the 6-inch pipe.

158. Description of the Terminal Well. The terminal well (fig. 17) is a reinforced concrete structure, 6 feet 8 inches wide by 8 feet 8 inches long and 26 feet 6 inches deep. Two coats of asphalt emulsion dampproofing compound were applied to the exterior surfaces of the terminal well walls. A 20 percent water solution of hydrochloric acid was applied to the interior walls and allowed to remain for about 5 minutes, after which the treated surface was scrubbed briskly with a stiff-bristled brush. The walls were then thoroughly rinsed with clear water and allowed to dry. Three coats of white VR-3, vinylresin paint were then applied to the interior surfaces.

A 2-inch tongue-and-groove, wood-frame, aluminum-covered roof was installed on the terminal well. A hinged 2- by 2-foot door was installed in the roof to permit access to the well.

The ventilation system was installed with the blower in the upper portion of the terminal well. A sawdust-insulated, frostproof door was installed 10 feet above the bottom floor of the terminal well. A 6-inch-diameter metal pipe was used for the air duct above the frost door, and a fabricated wooden duct was installed below the frost floor. An inline shutoff valve was installed between the manifold and each vertical row of needle valves to facilitate locating any leakage in the system.

159. Filling Piezometer Tubes with Water. Filling the piezometer tubes with water was started in December 1959 as soon as all of the equipment was installed in the terminal well. Water was pumped into the inlet tube, by means of the electric pump, until a return flow was noted through the outlet tube. If no flow was noted in the return tube after a reasonable length of time, the valves were reversed and water was pumped into the outlet tube.

Upon initial circulation it was found that no water could be pumped through the inlet or outlet lines of foundation tip 12 or the outlet tube of foundation tip 3. Attempts were made to clear the lines to tips 3 and 12 by connecting the tubes to a hand pump and pumping water directly into the line, bypassing the gage. This method was not successful, so connections were made to a bottle of compressed nitrogen with a pressure of 1, 800 pounds per square inch applied to each line. This method likewise proved unsuccessful in clearing the lines, and it was concluded that the inlet and outlet lines to tip 12 and the outlet line to tip 3 were probably ruptured; the lines were therefore abandoned.

At the close of the construction season of 1961, following a rapid rate of embankment construction, high pore-water pressures were observed. A discussion of these special observations is given in subsection 22(b).

160. Crossarm Settlement Installation. Two embankment settlement installations, designated as installations A and B on figure 12, were installed in the embankment of Navajo Dam. Details of the installations are shown on figures 14 and 15. The A installation is located at station 40+10, 20 feet upstream of the dam center line and consists of a total of 37 settlement units and 3 horizontal movement units. The horizontal movement units (fig. 104) were installed at elevations 5744. 35, 5872. 05, and 6016. 53. The B installation is located at station 40+20, 400 feet downstream of the dam centerline and consists of a total of 19 settlement units and 2 horizontal movement units. The horizontal units were installed at elevations 5756. 31 and 5894. 41.

A 2-inch base pipe was installed and grouted in a 4-inch-diameter hole drilled into bedrock. Oakum was wrapped around the top of the pipe and a pipe cover was set in place. When approximately 10 feet of embankment had been placed, the settlement installation was located by straddle hubs. A 2-1/2- by 4-foot excavation was made and an 8-inchdiameter hole was augered from the base of the excavation to the top of the pipe cover. The pipe cover was then removed and an 8-1/2-foot piece of 2-inch pipe with crossarm

was set over the 1-1/2-inch pipe and tamped in place. This method of installation was followed at both settlements A and B throughout construction of the embankment.

Two record tests were taken at each unit of the internal vertical and horizontal move ment apparatus in earthfill material. The tests included mechanical analysis, specific gravity, liquid and plastic limits, and percolation-settlement. The test results are included in appendix B of the final embankment construction report. 1/

As each crossarm was completed, the reading scale with adapter was placed on the 1-1/2-inch pipe, the measuring torpedo (fig. 16) lowered into the pipe, and readings taken on each crossarm. After the last reading, the torpedo was dropped to the latching plate and removed. In use, the depth of water in the crossarm system is measured by lowering an indicator device on an electrical cord to the water surface. A brass float in the device closes an electrical circuit when the device reaches the water surface and lights a bulb which is visible to the operator. The depth of the water level is indicated by the footage of electrical cord lowered into the settlement installation.

161. Surface Settlement Points. Forty-three surface settlement points were installed on 200-foot centers, on lines parallel to the centerline of the dam at 57. 5 feet upstream, 19 feet downstream, 271 feet downstream, 641 feet downstream, and 1, 006 feet downstream, as shown on figure 12. Installation details are shown on figure 13.

Each settlement point consists of a 1-inch by 5-foot reinforcement bar driven into the embankment. The bars were grouted to within 15 inches of the embankment surface. A mass of concrete about 15 inches in diameter was placed around the bars and above the grout, leaving approximately 1-1/2 inches of bar above the surface of concrete.