THE CAIRO BRIDGE.

11

The caissons are built of pine timber with oak sills and iron cuttingedges, planked with one thickness of pine plank laid diagonally, andone thickness of oak plank laid vertically. The caissons are allsurmounted by timber cribs of the same section as the caisson itself,and 34 feet high. The cribs are built of pine timber planked withtwo thicknesses of pine plank. The corners of the caissons and cribsare rounded and plated with tliree-eighths inch iron. Both the caissonsand cribs were filled with concrete, that in bottom of chambers, on roofof caisson and at top of cribs being made of Portland cement, sand andcrushed stone, Louisville cement taking the place of the Portlandcement in the other portions. The proportions of cement, sand andstone varied with the place and kind of cement used.

The caissons were built on launching aari} t s on the Illinois shore.The pneumatic machinery was set up on a barge. During the progressof the work, it was found convenient to have a second pneumatic plant,which was mounted on the old steamer “Ivate Elliott.” Material wasconveyed to the pier sites on barges. The work on the individual piers,except that of building and sinking Piers IX and X, was carried on inan intermittent way as the condition of the river, necessity, or conven-ience dictated.

PIER i.

Pier I was the last pier commenced, excavation being begun on June15tli, 1888. Pile driving was commenced August 27; the piles werecut off at elevation 139, September 10 ; concreting was begun September14, and finished on the 18th ; the masonry was begun on November 30,and the pier completed December 13th, 1888.

PIER II.

The framing of timber for the caisson for Pier II Avas commencedNovember 3. This caisson Avas originally intended for Pier VIII.The cutting edge Avas set up on launching Avavs on the 29th of NoA r em-ber and the caisson proper Avas launched on the 8th of February andbuilding of crib carried on AA’hile the caisson A\ r as afloat. On the 29tliof that month it Avas placed in position and the filling Avith concreteAvas commenced on the following day. Air Avas put on the 3rd ofMarch and sinking begun. The timber Avork Avas finished on the 15tliof the month and the concreting on the 17th. The masonry Avas com-menced on the 20th. In sinking this pier, some difficulty Avas ex-perienced in leveling it up and blocking aaris put under the cutting edge

to right it up. This was at first unsuccessful, but after a number ofsettlements, the caisson Avas gotten fairly into position. It reached itsfinal eleARition, after some intermissions in sinking, on the 8th of May,and the Avorking chamber Avas filled Avith concrete on the 13tli.Masonry Avas resumed on May 31 and carried on at odd intervals untilNovember 28, 1888, Avhen it Avas completed.

pier hi.

The framing of timber for the caisson of this pier Avas commencedon the 26th of December, 1887, the cutting edge placed on the 30th andbuilding begun at once. On January 18, 1888, OAving to high Avater,the caisson had to be loaded doAvn Avith iron to prevent its being floatedoff the launching Avays. On the 26th the Avater had gone doAvn suffici-ently to remove the iron and resume construction. The caisson Avaslaunched on the 16tli of February; on March 18, it Avas placed in posi-tion and concreting commenced the next day. Air Avas put on on the24th and building of the crib completed on the 30th and the concretefilling finished on the 31st. Masonry Avas commenced on the 7th ofAugust and sinking Avas carried on at intervals during the months ofApril, May, June and July. The caisson reached its final position onthe 29tli of July ; sealing Avas finished on the 3rd of August; masonryaaris resumed on the 5th, but stopped again on the 13th; resumed Novem-ber 19tli and the pier completed December 7, 1888.

PIER IV.

The first timber for the caisson AA - as framed March 19, 1888, and thecutting edge Avas placed March 20th. On April 22nd an effort aarismade to launch the caisson, but Avhen the lower side of the cutting edgeAvas nine feet under Avater, the caisson stuck on the launching Avay, and,notAvithstanding continued efforts, Avas not floated until the 4tli ofMay. On the 13th the caisson Avas placed in position and concretingAvas begun the next day. Air Avas put on temporarily on the 18th to con-nect pumps, and sinking aaris actually commenced on the 21st.Concreting Avas finished on the 24th and the planking of the crib thenext day. The masonry aaris commenced on the 26th, and sinking Avascarried on intermittently during the months of June, August and Sep-tember, the caisson reaching its final position on the 10th of Septemberand sealing Avas commenced that day. The Avorking chamber aarvs filledon the 13th ; the shaft holes Avere filled on the 17th and masonry aaris

resumed that day. It aaris again suspended from the 27th till Decem-ber 7, and the pier Avas finally completed on the 4th of January, 1889.

PIER AR

The framing of timber for this caisson aaris commenced April 24,1888, and the cutting edge set up on May 6. On the 21st the caissonAvas launched.and tOAA'ed to the contractor’s AA'liarf boat, AA’here con-creting aaris commenced. It aaris toAved to position on June 5 and airpressure put on .Tune 11. Concreting aaris finished on the 15th andthe timber Avork of the crib on the 16th and on the same day masoniyAvas commenced. Sinking aaris carried on as found convenient duringthe remainder of June, July, August and September, and the final ele-vation of the pier aaris reached September 26. Sealing of Avorkingchamber Avas commenced on the 27th and finished on the 29tli. Ma-sonry aaris resumed October 7, and after several intermissions, com-pleted January 17, 1889.

PIER AT.

The first timber for this caisson aaris framed May 14, 1888, cuttingedge placed June 16, and the caisson launched on the 27th. On July 2it Avas placed in position and concreting resumed. Air Avas first puton on the 5th. On the 14th timber Avork for the crib aaris finishedand on the 18tli concreting Avas completed. Masonry aaris begun onthe 19th. Sinking aaris completed on August 20, and the sealing ofthe Avorking chamber on August 23. The shaft holes were not filledtill September 15. Masonry aaris resumed on the 19th of that monthand the pier completed December 27, 1888.

PIER ATI.

Framing of timber for this caisson aaris commenced June 1, 1888 ;the cutting edge aaris placed June 28, the caisson launched July 17,and placed at its site on the 24tli. Concreting aaris commenced the nextday and sinking August 4. The crib AA’ith its concrete filling aariscompleted August 15, and masonry commenced on the 22nd. Sinkingaaris completed Ocober 4, the Avorking chamber sealed on the 7th,shafts finished on the 8tli and the pier completed Januaiy 19, 1889.

PIER AT1I.

The first timber for this caisson aaris framed on July 5, 1888. OnJuly 26 the cutting edge aaris placed and the caisson launched Au-