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April, 1913 bed. Each crib contains about 22,000 ft. of lumber and is held in place by loose rock filling. The cribs are made watertight by sheet piling faced with clay. When the river bed was unwatered, the excavation on the lock site was done by blasting and steam shovels, the rock being crushed and used for concrete. In the bottom of the lock is a grid- iron of culverts, as indicated in Fig. 5, the main being under the bottom of the east wall running lengthwise of the lock, while the laterals cross the lock floor at intervals of 45 ft. laterals are 6 ft. in diameter and the nipples connecting them with the floor of the lock are 3 ft. in diameter. The main ranges in diameter from 6 ft. at the lower end to 13 ft. at the upper end. The culverts are cast of concrete around a steel lining. There is a system of small temporary cof- ferdams which permit any culvert to be emptied and entered for inspection or repairs. The culverts are so de- signed that they will fill the lock in about 10 minutes. At the same time the culverts and floor of the lock were being built, work was progressing on the con- struction of the walls. The latter are reinforced concrete monoliths, the east one being continuous with the power house and the west one with the dry dock. Each wall is 52.35 ft. high and 33. ft: wide-at the base. At the top-are inset arches giving a wider causeway along the top. The The. THE MARINE REVIEW solid top of the east wall is 8 ft. wide and that of the west wall 20 ft.; the west wall is thicker because it is also the wall of the adjoining dry dock. ¥he Gates The gates and _ other machinery around the lock and dry dock will be operated by compressed air creat- ed by two water turbines set in the dam just east of the lock. Either turbine has sufficient capacity for the total operating requirements of the lock and dry dock. The lower gates, Figs. 9 and 10, are of the usual miter type and were fabricated by the Chicago Bridge & Iron Co., Chicago. They are each 125 which are of the buoyancy type and float into position over their seats. There are two gates at the upper end of the lock, one being a guard normal- ly inactive and the other the regular working gate. They are made to in- terchange with the dry dock gate so that any one of the three may be used at any position, thus preventing de- lays in operation of the lock through damage to the gates. A _ section of the buoyancy gates is shown in Fig. 7 and an elevation in Fig. 8. Each gate is simply a rectangular steel chamber approximately 18 ft. square and 110 ft. long. The buoy- ancy. chamber, which may be filled with or emptied of water, occupies the lower half of the interior of the FIG. 6--LOOKING UP-STREAM THROUGH LOCK 50. tt. oh and 115. tt, slong. the pivots, which are hardened steel work- ing in bronze bushings, are hemis- pherical 18 in. in diameter. when closed form an arc of a circle 66 ft. 434. in. in diameter with its convex side up-stream to present a maximum resistance against the pres- sure of the water in the lock. The framing of the lower gates is clearly indicated in Fig. 10. Provision has been made against the sag pull, ap- proximately 374,000 lb., by embedding steel members in the concrete walls opposite the gate hinges. The weight of the gates is also partly neutralized by 12 x 32-ft.. buoyancy chambers inside each leaf. Considerable interest is, attached to the construction of the upper gates The gates* gate, as indicated in Fig. 7. When in its proper position, the gate moves up and down in vertical slots of steel of a special design, which includes latches to fasten the gate in the closed position. Operation of the Locks When a boat wishes to enter a lock, the valves are opened which admit water into the buoyancy chamber in the gate: and permit the air therein to escape. The gate sinks vertically, as does a filling boat, until its top is a little below the sill beside which if rests. The guard gate in Pig. 7 is shown occupying this position. When the boat has entered the lock, the water in the buoyancy chamber is forced out by the compressed air and