THE NEW OMAHA BRIDGE.

5

m.

SUBSTRUCTURE.

The five piers are designated by letters, Pier A being the mosteasterly. This designation was adopted to avoid confusion with the oldpiers, which were numbered; the numbering being from west to east.

The five piers are founded on pneumatic caissons of the followingdimensions: —

Pier A,

65 feet long, 25 feet wide, and 18

Pier B,

65 “ “ 25 “

“ 18

Pier C,

66 “ “ 26 “

“ 18

Pier D,

65 “ “ 25 “

“ 18

Pier E,

65 “ “ 25 “

“ 18

The foundations were put in by the company’s men under thedirection of the Engineer. The masonry was built by contract by thefirm of T. Saulpaugh & Company.

The caisson for Pier A was built on the dry sand-bar on the eastside of the river. The other four caissons were built in position on pilefalse-work, and lowered by long screws to the bottom of the river.

The pneumatic machinery was set up on the east side of the river,south of the old Pier VI. It consisted of two No. 4 Clayton DuplexCompressors, the power being supplied by three old locomotive boilers.A Worthington Packed Plunger, Duplex Pump, with 18^-inch steamcylinder and iOj-inch water plunger, supplied the power for the sandpump excavators. These sand pumps were of a special pattern designedby me and illustrated on Plate 7.

A temporary pile bridge was built each year from the east bankof the river fifty feet north of the bridge line, extending during the firstseason as far as Pier C, and during the second season completely acrossthe river. A service track was laid on this bridge, and the Worthingtonpump was then set up on this bridge, steam being supplied from theboilers on the shore. The air for the caissons was led from the pumpsto Piers C and D by a pipe laid on the floor of the old bridge; this

arrangement being adopted so that the air supply could be kept up incase any injury occurred to the temporary pile bridge. During thesecond season the Worthington pump was put on a barge, and steamsupplied by two 60 H. P. portable boilers erected on this barge. Afterthe completion of foundation D the pneumatic machinery was movedfrom the east sand-bar and set up on the west side of the river.

The caissons were built of Oregon fir, with cutting edges of iron,strongly bolted together, and filled with Portland cement concrete. Thecaisson for Pier A is surmounted by 38 feet of crib-work, that for PierB by 13 feet of crib-work, and that for Pier C by 6 feet of crib-work ;the crib-work being filled with concrete similar to that used in thecaissons. The masonry of Piers D and E starts from the top of thecaisson. The framing of the caisson for Pier A was begun October29, 1885, the erection of the caisson November 6, and air - pressurewas put on December 15. The laying of masonry began January 11,1886, and the caisson reached bed-rock at elevation 35.72 on January31. The sealing of the working chamber was begun February 1, andcompleted February 8. The masonry was finished April 22, 1886.

The framing of the caisson for Pier B began November 27, 1885,the construction of the staging: December 2, the erection of the caissonJanuary 5, 1886, and the lowering with screws January 30. On February5 the caisson rested on the bed of the river, and air pressure was puton February 6. The laying of masonry began February n, and thecaisson reached the rock at elevation 28.62 on March 7. The concretefilling of the working chamber was begun March 9, and finished March12. The masonry for this pier was completed June 12, 1886.

The framing of the caisson for Pier C began June 28, 1886, theconstruction of the staging July 31, the erection of the caisson Au-gust 18, and the lowering with screws September 15. Air pressure wasput on September 17, and on the same day the caisson rested on thebed of the river. The laying of masonry began September 23, andthe caisson reached bed-rock at elevation 30.07 on October 20. Theconcrete filling of the working chamber was begun October 24, andfinished October 30. The masonry for this pier was completed De-cember 18, 1886.

After the completion of the foundation of Pier C, it was thoughtwise to discontinue the work until after the flood season of 1886.

The construction of the staging for Pier D was begun September14, 1886, the framing of the caisson September 15, the erection of the

caisson September 23, and the lowering with screws October 27. Airpressure was put on November 3, and on November 4 the caisson restedon the bed of the river. The laying of masonry began November 4,and the caisson reached bed-rock at elevation 40.80 on December 3. Theconcrete filling of the working chamber was begun December 4, andfinished December 7. The masonry for this pier was completedMarch 8, 1887.

The river closed by ice unusually early, — on November 18, 1886;but it was not thought safe to begin work on the construction of PierE until the season was so far advanced that there was thought to beno danger of this ice moving. In the intervening time the pneumaticmachinery was moved from the east to the west side of the river.

The construction of the staging for Pier E was begun October19, 1886, and the framing of the caisson was begun on the same day.The erection of the caisson was begun on November 28, and the lower-ing with screws began January 5, 1887. Air pressure was put onJanuary 9, and on January 10 the caisson rested on the bed of theriver. The laying of masonry began January 12, and the caisson reachedbed-rock at elevation 46.43 on February 17. The concrete filling of theworking chamber was begun February 19, and finished February 22.The masonry for this pier was completed April 7, 1887.

The full details of the five piers, the caissons, the air-locks, andthe appliances used in connection therewith, are given on Plates 2, 3,4, 5, 6, 7, 8, and 9. The rate of progress in sinking is illustrated graphi-cally on Plate 10. Full records of the progress in detail of sinkingthese foundations were kept, and are given in Appendix C. The de-tailed cost is given in Appendix D.

The concrete used was manufactured in a mixer consisting of a9-inch spiral conveyor with teeth arranged between the flights, andrunning in a wrought-iron trough. The sand, cement, and water weremixed in this mixer, and the stone was put in after depositing the con-crete mortar in position, the stones being thrown in by hand and thewhole mass thoroughly rammed. Inside of the working chamber nostone was used. The proportions of sand to cement varied from twoto four parts of sand to one of cement, the cement being Portlandcement except in some unimportant instances.

The cost of the five foundations is shown in detail in the follow-ing table; this cost including all concrete and other material below themasonry: —