THE MEMPHIS BRIDGE.

9

After the adjustment of the structure, folding wedges were placed be-tween the steel plate and the blocks and tightened up so as to preventany possible horizontal bending strain on the anchor-rods.

The other five piers all have deep foundations which were put inby the plenum pneumatic process. Two of them, Piers I and V, comeon dry ground during high water. Pier IV comes at the edge of thewest shore as it was ten years ago and as it is now being restored by theprotection work. The other two piers, II and III, come in the mainchannel. Piers I, II, III, and IV are all of similar shape, with straightparallel sides and ends formed of two circular arcs meeting in points,except above high water, where the ends are semicircular. They are ofthe same general plan which the Chief Engineer had used on other simi-lar structures of less magnitude. The plans of these piers, showing themasonry as actually built, are given on Plates 11, 13, 14, and 19.

The masonry was all built by contract by Mr. Lewis M. Loss. Theexposed portions of all these piers are of granite from Lithonia, nearAtlanta, Ga. The backing throughout and the face stones of the lowercourses are of limestone from Bedford, Indiana. Piers I, II and IIImeasure 12 feet thick and 47 feet long at their least dimension, which isunder the belting course. Pier IV is 10 feet thick and 43 feet long atthe same place. Pier II is hollow below elevation 212 ; Pier III is hol-low below elevation 195.6. Pier IV has niches on the west side to carrythe end of the deck-span. The specifications for the masonry are givenin Appendix K.

No attempt was made to make the lower portion of the chambers inthe masonry water-tight, but the water rises and falls in the hollow ma-sonry. To prevent any internal air-pressure from this source, the twoend spaces are connected with the central spaces near the top by four-inch horizontal pipes, and a pipe from six to four inches in diameter wasbuilt near the centre of the pier, extending vertically from the top of thechamber to the coping, and terminating in a cap flush with the top ofthe coping. In the cap a small hole is drilled.

The concrete used was composed of crushed limestone, sand, andcement. The sand was dredged from the bottom of the MississippiRiver and of excellent quality. The cement used generally was thenatural American cement manufactured at and near Louisville, Ky.; inspecial portions of the work German Portland cement was used. Theconcrete was generally mixed in a machine mixer made by the CockburnBarrow and Machine Company of Jersey City, N. J.; its capacity wasabout 20 cubic yards per hour. The mixer, together with a derrick and

hoisting-engine, was carried on a barge 90 feet long, 30 feet wide, and 5^feet deep. A platform large enough to handle three batches of concretewas built on the barge about five feet above the deck and the mixerplaced under this platform. The cement and sand were first thoroughlymixed together, spread over the crushed rock and shovelled while dryinto the mixer where the water was added. The mixer discharged theconcrete directly into dumping-buckets, and the derrick delivered thebuckets where wanted.

The concrete above the working-chamber was generally made in theproportions of one barrel of cement to 74 cubic feet of sand and 13£ cubicfeet of crushed rock. In the lower portion of the V-shaped walls, wheresome leakage-water was present, the proportion of crushed rock was re-duced nearly one half. Louisville cement was used everywhere above ahorizontal plane two feet above the roof of the working-chamber, exceptin contracted places around the air-locks and working-shafts; in theseplaces Portland cement was used. The concrete used to fill the working-chamber was generally mixed in the same proportions as that used above,but the amount of crushed rock was reduced in all places difficult ofaccess; the lower two feet of concrete was mixed entirely with Portlandcement, and the six inches of filling under the shoulder of the cuttingedge, the cross-walls, and the flat surface of the roof were a Portlandcement mortar, three parts of sand to one of cement and without stone;all other parts of the filling were the usual Louisville cement concrete.

The five numbered piers are founded on hard clay (into which itAvas desirable to sink them several feet) and at depths which it was ex-pected would vary from 60 to 100 feet below low water. The fact thatthey had to be sunk to and into a clay Avhich was too hard to be ex-cavated by any dredging process made it expedient to use the plenumpneumatic process, and this was decided on from the start.

As the work was of unusual magnitude, it was thought unwise tohave it done by contract, and a force was organized to do the work underthe direction of the resident engineer.

The full equipment provided for handling the work in the river con-sisted of the following:

Two steamboats with pneumatic plant complete.

One tugboat.

Two anchoi’-barges.

One derrick-boat.

One pile-driver boat, used also as a derrick-boat.

One boat with concrete-mixer.

One house-boat for workmen.

Tavo barges Avith weaving ways for mattresses.

Seven material barges.

The tAvo steamboats were each built originally to serve as transfer-boats on the Missouri River. They were side-Avheel boats of the typecommon on western rivers, each having four high-pressure boilers andtwo long-stroke poppet-valve engines, with independent Avheels. Thespace in the middle of the boat usually occupied by the track for carswas roofed over, and in this space Avere placed two No. 4 Clayton air-compressors each having two steam and two air cylinders 14 inches indiameter and 15 inches stroke; one large Worthington pump with steam-cylinders 18| inches diameter, water-cylinders 10£ inches diameter, with10-inch stroke, and an incandescent electric-light plant. One of thesesteamers, the JOHN BERTRAM, had been used previously at the Ruloand Nebraska City bridges; the other, the JOHN F. LINCOLN, wasfitted up for this work with machinery which had previously been usedon the Sioux City Bridge. They both proved very efficient tools. Thenine barges last mentioned were ordinary coal barges used on the Mis-sissippi River, 25 feet by 130 feet and 7 feet deep; they were deckedover to fit them for use. This plant was exclusive of the floating plantused by the masonry contractor.

The general organization of the pneumatic force employed on thepneumatic foundations was as follows:

Pressure Force.

1 principal foreman.

1 night foreman.

3 to 8 gang foremen, the number depending on the depth.

2 lock tenders.

12 clay hoist tenders.

60 to 120 pressure men.

Machinery Force.

1 master mechanic.

3 machinists.

4 steamboat engineers.

4 firemen.

4 coal-passers.