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Jilly, 1912 spoil and the introduction of. struc- tural material being accomplished through the square openings left in the bracing. When the entrance was completed, this bracing was removed and inclined braces resting on the granite sills held the face of the cof- ferdam against external pressure. Owing to obstruction from the steel Sheet piling left by the early con- tractors, it was necessary to make a digression in the line of the cut-off wall for a portion of the distance on both sides to permit this piling to be removed in the open interior ex- cavation, made after the caissons were in place. Much of this had to be cut with the oxyacetylene torch, as it was impossible to pull it. Floor Construction When the cut-off wall and interior piers were all in position, the work of placing the floor began. The op- eration consisted of excavating a strip to subgrade from wall to wall, and placing in position struts made of four 12 by 12-in. timbers' connect- ed by lattice bracing, and: bolted so as to act as one piece. Inequalities in length were takén up by. short timber balks and _ paired wedges. These trusses were spaced 20 ft. center to center, and second, and in some instances, third tiers were placed and keyed, and_ longitudinal and sway bracing provided. The ex- cavation between two adjacent struts was then carried to sub-grade and a strip of 'floor laid and finished. A -space on each side was left undis- turbed and other strips laid. When 'sufficiently set, the bracing was re- moved and the remaining segments of floor placed in position between the strip already in place. As the work progressed it was found possible to open wider spaces, and one piece of floor 45 ft. long, involving 1,700 cu. yds. of concrete, was put in place in 26 hours. Holes in the floor provided for the pumping of infiltered water, thus re- lieving pressure on the floor until the side walls had been placed in suffi- cient mass to provide the necessary stability, when they were sealed, con- nections being left for pressure gages, by means of which it was found that the floor was successfully resisting 'the full hydrostatic thrust estimated on. Dock Lining, Etc. With the exception of the coping, abutment and gate sills, which are of New England granite, the facing of the dock is of hard burned vitri- fied brick, except at the head, above the stair line, where the face is con- crete. The 14 stairways are of con- 'of the THE MARINE REVIEW crete with Wainwright nosings. . Ten material slides are provided, 6 ft. wide, each side of each slide being an expansion joint. Floating Caisson Gate The gate for this novel structure is also a novelty in the United States, being of the hydrometer type which has recently been proved~ successful in European docks. The pumping. equipment is located in a well near the mouth of the dock, being an irregular pentagon abutting on the dock wall, built in caissons, similar to the cut-off wall and keyed to theni.. It is approximately -28. ft, wide and 50 ft. long. The pumping equipment consists of. three vertical shaft, one-stage volute pumps, driven by 48 pole, three-phase, 60-cycle, 2,300-volt induction motors, with 54- in. diameter intakes and 48-in. diam- eter discharge ends. These pumps have a rated minimum capacity of 8,800 cu. ft. per minute under the maximum head, and are capable of emptying the dock in one hour and 20 minutes continuous run. Two 15-in. pumps of similar type are pro- vided to handle the water below the vacuum level of the large pumps and to handle drainage. Both sets of pumps are provided with motor-driv- en stop valves, and necessary checks. The floor of the dock is. provided with four openings, 16 ft. by 6 ft., which connect directly by tunnels 6 ft. square to a forebay in the mass dock wall. . The discharge is into a. culvert built into the wall, 10 ft. wide by 16 ft. high, and open- ing to free water outside the gate. The floor is also traversed for its full length by two drains, 3 ft. diam- eter, with intakes 4 ft. apart, to facilitate the removal of water im- pounded between the blocking on the floor, and to handle drainage when a ship is in dock. These con- nect with the openings into the fore- bay. Supply Lines Electrical service is supplied through conduits laid in the side walls, with numerous manholes, and outlets on the face of the dock above high water. Submerged outlets with watertight connection boxes are also provided at two points below water level. Salt water, fresh water and com- | pressed air are supplied by 6-in. diameter mains encircling the struc- ture with branches to the face of the dock wall. Three capstans are provided on each side, and one on the center line at the head of the dock. Nineteen bollards, of obsolete guns set in con- Zoo crete. blocks, are placed at regular intervals along the sides. A crarie track, 18 ft. gage, encircles the dock, the inner rail resting on the coping and the outer rail on a continuous concrete girder 8 ft. deep, supported on piles, providing a run- way for the 40-ton cranes used in connection with the dock. Another rail, at standard gage from the in- side crane rail, provides for small locomotive cranes and other standard gage rolling stock. A standard gage track also crosses the caisson gate, connection being made at either end to the yard railroad tracks. Figure 1 shows these details clearly. The plan, as outlined by Mr. Har- ris and carried to successful com- pletion by Fred Holbrook, who had. immediate charge of the work for his firm, has been successful in all respects, and the completed dock was emptied for a ship on May 9, 1912, only two years and a half after work began. In the caisson work, 32,000 cu. yds. of concrete was placed. The remain- ing work required approximately 60,- 000 cu. yds.; 2,000 tons of reinforc- -- ing steel were used. The total cost is about $3,000,000. Taking into con- sideration the fact that the work has been completed in the remarkably short time above mentioned, includ- ing over a year in caisson work alone, the interference from obstructions left by former contractors, the novel con- ditions to be met and provided for, often on the spur of the moment, and . the unusual co-operation between en- gineers and contractors, it is safe to say that a record for speed and economy in work of this character has been successfully established; and that all concerned have a legitimate source of pride in its successful con- clusion. Trial Trip of Battleship Arkansas The: 'official. figures of) the. recent builders' trial trip of the battleship Arkansas have just been compiled by the trial board. The performance ex- ceeds contract requirements. The fastest mile run on the _ standardiza- tion trial was 21.493; average of five high-speed runs, 21.153; average of four-hour run, 21.51; average of two- hour run, 20.989; maximum _horse- power developed, 29,271. The Western Maryland Railroad Co. has awarded to the Skinner Ship- building & Dry Dock Co., Baltimore, a contract to build two car floats for the company's service in Balti- more harbor. They are to be dou: ble-tracked, 230 ft. long, 33 ft. beam and 8 ft. deep.