The New Croton dam is one of the largest that has been completed to date. The quantities involved are 1,821,400 cu. yd. earth excavation, 400,250 cu. yd. rock excavation and 855,000 cu. yd. of masonry. The foundations were at a depth of 75 ft. to 100 ft. below the river and the pit was open so that pumping was necessary for about five years. The amount of water pumped when the pit was deepest varied from 5,000,000 to 8,000,000 gal. per twenty-four hours, depending on the weather and the stage of the river. (For a description of the river diversion works see page 34.) More than $100,000 was spent in opening quarries which for various reasons had to be abandoned. The quarry which supplied most of the stone was 6 miles from the dam to which the stone was transported by locomotives and cars on 36-in. gage tracks. Work was begun in 1892, but in addition to the magnitude of the work, various causes operated to delay its completion till early in 1906. Owing to a change of plans, an embankment and core wall section at one end was taken out and replaced by the regular masonry section, built however of cyclopean concrete instead of rubble.
Steam was generated and used in a large number of detached units. The principal items were eleven 10-ton, 36-in. gage locomotives, thirty-nine steam boilers 10 h.p. to 100 h.p. with total capacity of 1400 h.p., three steam shovels, dredge, fifty-five hoisting engines 15 h.p. to 24 h.p., eleven other steam engines 10 h.p. to 50 h.p., fifteen steam pumps total capacity 20,000,000 gals, per day, three 75-h.p. cableways, three stone crushing plants and eight mortar and concrete mixers. It cannot be stated how much of the above plant was in use at any given time. Undoubtedly an appreciable per cent, of it was duplication, renewals, reserve, in repair shops, etc., and could not be counted in average plant employed. Also some items as pumps, steam shovels and dredge were largely employed below river level and consequently do not figure in subsequent operations. The maximum force employed was 475 men on the dam and 376 men in the quarry. The maximum month (in 1898) laid 17,186 cu. yd. of rubble masonry. During the maximum month (Aug., 1904) on cyclopean concrete laid 17,000 cu. yd. Work was generally suspended in winter. When work was in full progress the consumption of coal was about 10,000 long tons per year. The total coal consumption for the entire construction period was 90,377 long tons.
At the Ashokan (Olive Bridge) reservoir (recently completed as an addition to the water supply of New York City) the water is retained by a large masonry dam and several dikes of earth embankment and core wall. The masonry dam is 1000 ft. long, and at the maximum is 250 ft. high and about 190 ft. thick at the base, containing 488,200 cu. yd. Each end is continued by a core wall embankment so that the total dam is 4800 ft. long. North and east of the main dam is a long dike, sections of which are known as West Dike, West, Middle and East portions of middle dike; further east is the East Dike and at its east end is the waste weir. North of the West Dike is a weir dividing two portions of the reservoir; this consists of 1100 ft. of masonry for an overflow section and about the same length of embankment with core wall. The total length of dams and dikes is 3.8 miles. The quantities of main items involved are 2,055,000 cu. yd. earth excavation, 425,000 cu. yd. rock excavation, 800,000 cu. yd. of concrete and cyclopean concrete masonry, and 7,360,000 cu. yd. of earth and rock embankment.
The main power plant, near the north end of the Masonry dam, consists of five 265-h.p. Babcock & Wilcox boilers, two 500-h.p. air compressors (formerly used at the Wachusett dam) each with a capacity of 3310 cu. ft. of free air per minute, two other similar machines each with a capacity of 2500 cu. ft. of free air per minute; also two generators for lighting purposes one 250 volt 140 amp. and the other 125 volt. 80 amp. The compressed air is piped to all parts of the work. From the dam the quarry is reached via about 3 miles of double-track standard-gage railroad with grades of 2 1/2 per cent, down from the quarry and 1 per cent, up from the low point to the dam; nine 40-ton to 60-ton locomotives are in use.
The stone and concrete are brought under four 15-ton Lidgewood cableways of 1534-ft. span, mounted on towers 90 ft. high, which travel 600 ft. up and downstream. They deliver all of the materials to the derricks on the masonry. In the quarry are two crushers, a No. 7 1/2 and a No. 5 McCully. At the main crushing and mixing plant near the head towers are one No. 9 McCully crusher and two No.
6 Austin crushers, four 2 1/2-cu. yd. cube mixers, screens, elevators, conveyors, etc. Also near the head towers is the yard 500 ft. long X 200 ft. wide for the manufacture and storage of concrete facing blocks. The stone at the quarry is a bluish-gray sandstone occurring in horizontal layers up to 3 ft. or 4 ft. in thickness. The quarry face is some 1200 ft. long and 30 ft. to 40 ft. high, worked in two lifts by Rand air drills which are run by air from the central plant. The output is about 1000 cu. yd. per day. In the quarry are ten derricks, in the concrete block yard are ten, at the crushing and mixing plant two, and on the masonry sixteen. All derricks are run by double 7-in. X 10-in. cylinder double-drum engines.
Employed on the various dikes and weirs are seven or eight steam shovels, about a dozen steam rollers, two Western graders, two road machines, two traction engines, two narrow-gage locomotives, two cableways, several derricks, crushers, mixers, etc. Although air is piped to all except a few of the more remote parts of the work, coal is of course burned under a number of detached boilers in addition to the steam shovels, locomotives, rollers, etc. Power is supplied to carpenter, machine and blacksmith shops and to a number of pumps. The main pumping plant has a capacity of 800 gal. per minute with a lift of 230 ft.
During the month July 21 to August 20, 1909 progress was as follows:
48,470 cu. yd.
4,455 cu. yd.
Embankment and refill................
114,230 cu. yd.
Concrete masonry in core walls...........
17,016 cu. yd.
17,000 cu. yd.
Concrete blocks set...............................
1,010 cu. yd.
Concrete blocks manufactured......................
4,010 cu. yd.
At this rate of progress, the above-described plant, central station and detached units, consumed about 1400 tons of coal per month. During higher rates of progress attained since, the coal consumption was about 2000 tons per month.
At the Kensico dam the materials are all assembled and brought within reach of the derricks by means of standard-gage locomotives and cars. The quarry is situated about 3/4 mile from one end of the dam, but in order to overcome differences of elevation through which the materials must be handled, there are several switchbacks in the system of tracks and the average total haul for the stone is some 2 1/2 miles. The haul for the sand is about 4 miles additional. The sand cars are filled about two-thirds full and hauled to the quarry where they are further filled to their capacity by screenings drawn from bins at the main crushing plant. They are then hauled to the gravity mixers at the dam of which there is one at each end, and dumped into bins. The large stones are loaded by derricks. The material going to the crushers is largely loaded by steam shovel. There are some five or six quarry openings, totaling perhaps 1/2 mile of face and employing twelve derricks. At the crushing plant in the quarry is installed the following: one large jaw crusher with opening 5 ft. X 7 ft., to take 10-ton stone, swing jaw 13 ft. X 7 ft., two 12-ft. diameter 15-ton flywheels peripheral speed 3400 ft. per minute, overall size 24 ft. X 15 ft. X 13 ft. high, total weight 225 tons, run by a 300-h.p. motor; a second jaw crusher with opening 3 ft. X 6 ft. flywheels 8 ft. in diameter peripheral speed 5000 ft. per minute, overall size 13 ft. X 13 ft. X 9 ft. high, total weight 105 tons, run by a 150-h.p. motor; a set of 60-in. diameter X 30-in. crushing rolls operating at 50 r.p.m., capacity 300 cu. yd. per hour reducing from 4-in. size to 2-in., run by a 100-h.p. motor; elevator and screen run by a 50-h.p. motor and two conveyors 5 h.p. and 15 h.p.