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CANAL OUTLET WORKS
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Figure 23. --Canal outlet works—Gate installations.
base pressures computed for the stability analysis. The stilling well shaft was considered as being subjected to a horizontal saturated-earth-fill load and a thrust at the walls of the gate chamber. The fill behind the stilling well wing walls was considered saturated to the top of the walls, elevation 2709.0. A saturated fill and a horizontal equivalent fluid load was considered acting at the heel of the wall. The toe and front face of the wall was considered unloaded. The walls of the gate chamber from elevation 2678.92 to elevation 2708.17 were considered loaded with horizontal earth pressure equal to one-half of the vertical load for the elevation considered. For settlement conditions in fill or structure, a horizontal load equal to three-fourths of the vertical load was investigated.
For design of the control house roof and floors at elevations 2695. 67 and 2708.17, the following loadings were used:
Roof of control house
Floor, elevation 2708.17
Floor, elevation 2695.67
The gate frame and conduit liner encasement were designed for a hydrostatic head for a maximum reservoir water surface elevation of 2785.0.
32. High-Pressure Gates. - Two 4- by 4-foot high-pressure gates are installed in the canal outlet works, one in an emergency gate chamber and the other in a regulating gate chamber in the gate control house. The gate in the emergency gate chamber is for emergency use only and is provided with a semiautomatic gate hanger for holding the gate in the wide open position. The gate in the control house is for regulating the flow of water through the outlet works and is provided with a hydraulic gate hanger for holding the gate at any required opening. Gate installations are shown on figure 23. With the gates 100 percent open, the reservoir water surface at elevation 2720.0, and the canal water surface at elevation 2705, the canal outlet works has a capacity of 300 second-feet.
Air inlet connections, connected to vent pipes, are provided on the downstream frames of both gates. There are two flanged bypass openings on the left side of the horizontal centerline of both upstream and downstream frames of the emergency gate. An 8-inch pipe with control valve provides a connection between these openings and is used for filling the outlet conduit when the emergency gate is closed and prior to opening of the emergency gate.
Each gate is operated by a hydraulic cylinder hoist, having a capacity of 85,000 pounds with the oil pressure in the oil cylinder at 750 pounds per square inch. The design of these canal outlet gates and hoists is the same as discussed for the river outlet gates and hoists in section 24.
33. /Miscellaneous Equipment. - Two identical pump units are provided for lifting water from a sump, located at the downstream end of the conduit and under the control gate chamber, and discharge it through piping into the outlet canal. The sump collects seepage and/or drain water from the conduit, the stilling well and control gate chamber floor. Each pump unit consists of a vertical-shaft, turbine-type pump, directly connected to a vertical-shaft, 5-horsepower electric motor. Each pump is designed for a discharge of 200 gallons per minute against a pumping head of 46 feet. The pumps are supported from the floor of the control house at elevation 2708.17 and discharge water
at elevation 2706.0 into the outlet canal. The discharge piping is provided with check valves which prevent backflow through the piping from tailwater in the canal and also prevent backflow through one pump while the other pump is running. A
The control for each motor permits either manual or automatic operation through a float-controlled switch and alternator arrangement. Under automatic control, one pump starts and stops at sump water elevations 2667.0 and 2665.0, respectively, and the other pump starts and stops at sump water elevations 2668.5 and 2666.0, respectively. By means of the alternator the pump starting sequence is transposed at the beginning of each successive pumping cycle.
An oil hydraulic system is provided for the control of high-pressure gates of the river outlets and canal outlet works . The system consists of an oil pump, electric motor, supply tank, 4-way valve (one for each gate), and piping. The oil piping is connected to the hydraulic gate hanger of the regulating gate in such a manner that the hanger releases the gate before oil is passed into the hoist cylinder, to raise or lower the gate.
A ventilation system is provided for the canal outlet works. This system consists of an air inlet, a fan unit, a duct from the fan to the emergency gate chamber, an air discharge head in the control gate chamber, and a starting switch for the fan motor. The fan unit draws air through an inlet in the roof of the control house and discharges it through a duct and discharge head into the gate chamber. The air from the gate chamber flows through the conduit and to the outside through a louver in the control house door. The fan has a capacity of 230 cubic feet per minute against 2 inches of static water pressure. The fan is started and stopped manually by a switch mounted in the control house.
E. Railroad Structures
34. Railroad Structures. - (a) Bridies and Culverts.— Bridges were designed in accordance with the AREA "Specifications for Steel Railway Bridges" and "Specifications for Concrete and Reinforced Concrete Railroad Bridges." Concrete piles were designed for loads of 36 tons, steel piles for 50 tons, and timber piles for 27 tons. Culverts were designed in accordance with standards of the Chicago, Burlington and Quincy Railroad Co., employing rigid-frame design principles. Both the bridges and the culverts were designed for an E72 loading. Loadings were based on the "American Railway Engineering Manual, " 1948 edition. Allowable steel and concrete stresses are given in appendix F. In the design, the weight of embankment was taken as 105 pounds per cubic foot.
(b) Roadbed.— To accommodate the weathering characteristics of the loess used in roadbed construction, the steepest embankment slope for normal conditions was established as 1-3/4 to 1. Subgrade was plowed or scarified, soaked by sprinkling if necessary, and compacted by a tamping roller. To stabilize the subgrade surface, a 6-inch layer of fine material from quarry waste was placed and rolled.
CHAPTER IV--CONTRACT ADMINISTRATION AND SURVEY WORK
35. Government Organization. - The construction engineer's staff for Trenton Dam was generally similar to that used on most Bureau projects. During the relocation and dam construction work, dual organizations for field engineering, office engineering, inspection and surveying were set up. The staff of the two organizations were interchanged as the work loads required. An organization diagram is shown on figure 24.
Figure 24.--Government organization chart for Trenton Dam.
(a) Laboratory.— A laboratory was provided and staffed with personnel for performing the required tests and inspections. These included tests on concrete materials and placements, inspection at mixing plants, and tests of earth materials during excavation and embankment placement. Laboratory forces supervised and assisted in installation of technical apparatus on the dam embankment. Settlement and piezometer readings were taken by the laboratory personnel during dam construction.
(b) Surveying.-- Survey parties started working in the Trenton Dam area during October 1947. A tentative dam axis was established soon afterwards for use in locating test drill holes. Topography for the general area was prepared on planetable sheets with a horizontal scale of 1 inch equals 100 feet and a contour interval of 5 feet. In the spring of 1949, the dam axis was established at a true bearing of N2°00'00"W. Permanent monuments consisting of brass caps set in concrete were placed in the ground so that approximately 4 inches protruded above ground. The station, offset from centerline or coordinate, and the elevation were stamped on the brass cap of each monument. Those permanent monuments were guarded with three fence posts to keep traffic away from the immediate area.
Horizontal control for the dam was established from the dam axis. Brass cap monuments were set at stations 7+72.77, 20+00, 81+00, 90+00 and 92+00. All horizontal controls for the dam, structures, and borrow areas were established from these five
monuments. Permanent monuments were set every 500 feet, both 800 feet upstream and 800 feet downstream from the dam axis. As the work progressed, the permanent monuments were augmented by numerous temporary monuments which usually consisted either of 2- by 2-inch oak stakes or 3/4-inch round reinforcement bars driven flush with the ground surface. The temporary monuments were guarded with flags and guard stakes. Elevation and coordinate information was written on one of the guard stakes.
Vertical control for all work on Trenton Dam was taken from permanent U. S. Coast and Geodetic Survey benchmarks located along the old Chicago, Burlington and Quincy Railroad right-of-way. From these benchmarks, vertical control circuits were extended to all permanent monuments in the dam and borrow areas.
The dam area was slope staked for stripping operations. After stripping, fill stakes were set for the downstream limits of the dam embankment and the upstream and downstream limits of the pervious zone. Detail cross sections were taken of the entire dam area after completion of stripping operations, to be used for determining excavated quantities. As the dam embankment progressed, the upstream and downstream slopes were maintained to line and grade by setting either slope or grade stakes. It was necessary to set these stakes for approximately every 5- or 10-foot vertical increment of embankment placed.
Control for line and grade of the spillway was maintained by four permanent monuments set outside of the working area. Two of these monuments were set on the centerline of the dam and the other two were set at right angles to the centerline of the dam and on the centerline of the spillway. From these monuments other monuments were set as the need arose.
Drift pins were driven into shale as control points for excavating for tile drains and cutoff trenches in the spillway chute. The forms for the floor cutoffs were also built and checked from drift pins. The upper portion of the spillway floor slabs was completed before much work was done in the gate structure area. This was advantageous in setting up control for the gate structure area. A number of offset lines were set in the spillway floor by using lead plugs and tacks. Control lines were established on the centerline of each spillway pier on offsets from construction joints, and on the centerline of the spillway. These controls were used for building and checking of forms. After outside forms of a placement were completed, line and grade work for all interior formwork, blockouts, curved sections, etc., was established.
Control for line and grade of the canal outlet works was similar to that used on the spillway structure. A set of lead plugs set on the centerline were used for control in placing the upstream section of conduit, which was placed into position as a unit.
36. Safety. - The Government employed a full-time safety inspector for Trenton Dam. The safety program for the contractors was conducted by their supervisory personnel. Monthly safety meetings were conducted during the construction program.
A perfect safety record was achieved on the project by several contractors who completed their contract work without accident. These contractors with their work are listed below:
(1) American Bridge Company--Erection of high railroad bridge superstructure.
(2) Nichols Construction Company--Relocation of county road.
(3) Asbell Brothers—Reservoir clearing.
Government vehicles were operated throughout the entire job without accident.
The following is the safety record for the entire job, requiring approximately 3, 000, 000 man-hours:
Number of lost-time accidents, including
Total lost-time, man-days 18, 544