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24, 568. 50 484,101.80
inside-pipe-size brass fittings and pipe were used. One-fourth-inch outside-diameter plastic tubing was used in the terminal well, and all connections were made with flared-type brass fittings.
The terminal well including ventilating blowers, air ducts, and ladders were installed by the contractor. The personnel from the residency staff installed the gates, manifold piping, and all plastic tubing in the terminal well, placed the system in operation, and took initial readings. No difficulty was encountered in securing balanced readings after all air had been removed from the tubing.
41. Embankment Settlement Apparatus. - The embankment settlement apparatus (fig. 32) consists of a series of telescoping 1-1/2-inch and 2-inch pipes having lengths of 3 feet and 4 feet, respectively. Three-foot sections of channel iron are bolted and welded at right angles to the middle of the 3-foot lengths of 1-1/2-inch pipe.
Each anchored pipe section and crossarm moves with the embankment surrounding it and is independent of the rest of the installation, thereby permitting measurement of differential movement between successive crossarms. The crossarms in each installation are installed at 5-foot nominal intervals and their alinement is such that any two successive crossarms lie in vertical planes at right angles to each other. A special engaging device, or "torpedo," is lowered into the pipes by a steel measuring tape to obtain elevations of the crossarm at their respective measuring points, beginning at the upper crossarm and continuing to the bottom of the installation. In this operation the lower end of the crossarm is engaged by pawls in the torpedo and the tape is tightened against the pawls and the exact location of the crossarm measured by means of a measuring scale. When the measurements are completed the torpedo is permitted to strike the latching plate ax the bottom of the installation, which causes the pawls to latch closed allowing the torpedo to be withdrawn. A comparison of the measured elevations with the original elevations gives the vertical movement of the embankment.
Two embankment settlement installations, comprising 63 crossarms, were made in O'Sullivan Dam. Installation A, consisting of 37 crossarms, is located 45 feet upstream from axis station 170+10 with the base crossarm established on top of lean concrete in the base of the cutoff trench. Installation B, consisting of 26 crossarms, is located 50 feet downstream from axis station 170+10 with the base crossarm set on undisturbed alluvium.
After the base crossarm was set and a pipe cover was placed on the 1-1/2inch pipe, a minimum depth of 6-1/2 feet of embankment was placed over the pipe cover. Then a trench about 2 feet wide, 4 feet long, and 3 feet deep was dug over the base installation and a hand-auger hole dug to expose the pipe cover. After sufficient material was removed around the pipe to permit the removal of the pipe cover without loose material falling into the pipe, the pipe cover was removed. Then the 2-inch pipe was slipped over the l-l/2-inch pipe of the preceding installation, and the next crossarm with oakum and pipe cover in place was inserted into the 2-inch pipe. The excavated material was then backfilled and hand tamped while the 2-inch pipe was held vertical (fig. 31). The placement of embankment was resumed and after placing another 6-l/2-foot lift over the pipe cover, the next crossarm was installed. Identical procedure was used in setting each succeeding crossarm. However, the long axis of the trench for any adjacent installation had to be rotated 90° about the centerline of the crossarm pipe from the axis of the trench of the preceding installation to permit their crossarms to lie in vertical planes approximately perpendicular to each other.
Surveyors of the resident engineer's staff established the base crossarm of each installation and determined the location of all subsequent crossarms. Elevation readings were taken after each installation. Prior to December 1, 1949, it was assumed that a base crossarm established on bedrock remained at a constant elevation which was used to determine elevations of other crossarms. On that date this practice was discontinued and elevations of all crossarms have since been determined from benchmarks outside the embankment area.
42. Surface Settlement Points. - Sixty-six surface settlement points were established on the surface of the completed embankment in five lines parallel to the axis of the dam (fig. 33). The number of points at each location are as follows: (a) 24 points located 25 feet upstream, (b) 24 points located 50 feet downstream, (c) 8 points