39. Housing. A housing project for Bureau personnel was located close to the east edge of Trenton, Nebr., in order that municipal water, sewer, and electrical facilities could be utilized. The project area consisted of about 7 acres of land.

(a) Houses. -- Houses for the housing project, consisting of twenty 2-bedroom and ten 3-bedroom houses, were constructed under specifications No. VII-18. Bids submitted in response to advertising for these specifications were opened June 17, 1947. Six bids were received. The low bid of $278, 640, submitted by Metcalf Construction Co., Omaha, Nebr., was accepted and contract No. 181r-1012 was awarded. The notice to proceed was acknowledged September 15, 1948. Two orders for changes, involving changes in design and materials, were issued during the life of the contract. A findings of fact extended the completion date for several subdivisions of the contract. The work was completed February 25, 1949.

(b) Pipe for Water and Sewer Facilities.-- Pipe for water and sewer facilities for the housing project were furnished and installed under contract by Jansen and Ells Construction Co., Beatrice, Nebr., who submitted the low bid of $24, 807. The work involved furnishing and installing about 8,000 feet of sewer pipe, 3,000 feet of water pipe, and miscellaneous fittings. The notice to proceed was acknowledged on August 19, 1948. A completion date of November 2, 1948, was established and the work was completed on October 30, 1948.

40. Caretaker's Facilities. - Caretaker's facilities, including a residence, garage and shop building, water and gas supply, and a sewer system, were constructed under specifications No. VII-111. Bids received in response to advertising for these specifications were opened March 16, 1950, at Trenton, Nebr. Four bids were received. The low bid of $25, 766.50, submitted by Northwest Realty Co., Alliance, Nebr., was accepted and a contract awarded. The residence, garage, and shop building are located on the left abutment approximately 500 feet from the dam.

41. Reservoir Clearing. The reservoir clearing work was accomplished under specifications No. 701C-222. Bids submitted in response to advertising for these specifications were opened November 27, 1951, at Trenton, Nebr. Thirteen bids were received. The low bid of $63,750, submitted by Asbell Brothers Construction Co., Riverton, Wyo., was accepted and a contract awarded. Notice to proceed was acknowledged on December 31, 1951, and a completion date of June 28, 1952, was established. The work was completed on May 8, 1952.

CHAPTER V--CONSTRUCTION

42. River Diversion. Several stages of diversion were used during construction of Trenton Dam. To meet diversion requirements, the river was successively confined in its channel; diverted through an artificial channel; diverted through another artificial channel near the old location of the Chicago, Burlington and Quincy Railroad; and diverted through the spillway.

Initially, the river was confined to its natural channel at about axis station 62+00. As construction work progressed, including excavation and backfilling of the cutoff trench and construction of the dikes, an artificial channel was excavated for diversion that crossed the dam axis between approximate stations 47 and 52. Because of heavy rains in 1951 and a steel strike in June and July of 1952, it became apparent that the embankment construction program would extend into 1953. In order to provide flood protection during the usual high-water months of May and June of 1953, it was necessary to revise the construction program, which required moving the river to a new diversion channel. In September 1952, the river was diverted through a channel near the original Chicago, Burlington and Quincy Railroad tracks which crossed the dam axis in the vicinity of station 79+00. Placement of embankment in the old diversion section was immediately started. The railroad was relocated in mid-December 1952. Early in May 1953, the river was diverted through the spillway and, by the end of the month, embankment work had sufficiently progressed to afford ample flood protection for the anticipated highwater season of 1953.

43. Construction Equipment. - The following is a list of the principal items of construction equipment:

Figure 26. --Main cutoff trench excavation operation. Well points were installed on the side slopes for dewatering the area.

A. Excavation

44. Foundation Area. The entire area to be occupied by the dam embankment, except that included in the cutoff trench and canal outlet excavation, was stripped to an average depth of 1 foot to remove all topsoil and all objectionable materials. Tractordrawn scrapers and motor patrol graders were used in the stripping operations (fig. 25). The removed materials were used in embankment construction or stockpiled for later use as topsoil on the downstream slope. All objectionable materials were wasted.

After completion of the stripping operations, water was applied to several areas in order to consolidate the foundation material with the embankment material. Approximately 26, 000, 000 gallons of water was ponded and allowed to seep into the foundation area between stations 7+00 and 21+00. After 2 weeks of ponding, auger holes were drilled and samples taken to determine the amount and depth of water penetration. Steel rods were driven at several places to determine preloading consolidation. Foundation settlement crossarms were installed at stations 15+00 and 21+00 (see chap. VI). After completion of this work and prior to embankment placement, the entire foundation area was smoothed and rolled.

45. Main Cutoff Trench. The main cutoff trench extends from about station 90+00 to station 22:50, where it connects with an auxiliary cutoff trench which forms the foundation of the canal outlet works. The centerline of the trench is 100 feet upstream of the dam axis from station 22+50 to station 76+10, where it is deflected at an angle and contacts the dam axis at about station 83+70. The trench, with a base width of 50 feet and side slopes of 2-1/2 to 1, was excavated in firm shale. Originally the trench was designed to extend 50 feet beyond the spillway structure, or to station 88+60. During excavation, it was considered advantageous to extend the trench to station 90+10 in order to lengthen the path of percolating water through the underlying sand strata and away from the spillway structure. Excavation operations are shown in figure 26.

Excavation work was started on August 1, 1949. Draglines and scrapers were used for the sand excavation. To prevent fracture of the shale surface, rubber-tired equipment was used when shale was encountered. Because of the river diversion requirement and anticipated winter shutdown by about October 15, excavation work was started in the area between approximate stations 44 and 54 and it was planned to complete the excavation and backfill work for river diversion before the winter shutdown. Fortunately, mild weather continued until December 10, and the contractor was able to complete considerable work in addition to the planned work. The excavation work was resumed in February 1950.

Because of the high water table in some sections of the trench, it was necessary to install well points and pumps for dewatering. This method was very successful. Because the well points were not embedded in the shale, shallow ditches and sumps were used to dewater the bottom 2 feet of the trench.

A major portion of the excavated material above the shale bedrock was satisfactory for use as backfill. The shale in the valley portion required only a minor amount of leveling and smoothing prior to placement of backfill.

46. Auxiliary Cutoff Trench and Other Excavation Work. The auxiliary cutoff trench is located with its centerline at dam axis station 22+50 and at right angles to the dam. This trench extends beyond the toe line of the dam and accommodates the canal outlet and control structures; it has a length of about 570 feet, a base width of 50 feet and side slopes of 1-1/2 to 1. The outlet works structure, averaging about 12 feet in width, is located along the centerline of the trench in from 4 to 9 feet of shale (fig. 27).

The excavation work was performed under two contracts.

Under the first contract the trench was excavated to the ground-water table elevation, and under the completion contract the trench excavation was completed to the required grade. All excavation work was performed with tractors and scrapers and all suitable excavated material was utilized in the dam embankment. Only a small portion of the material was wasted.

A well point system and pumps were installed around the perimeter of the auxiliary cutoff trench excavation for dewatering during excavation operations below the