4

THE RULO BRIDGE.

II.

GENERAL DESCRIPTION.

The Rulo bridge is a single track railroad bridge. It consists of threechannel spans each 375 feet long between centers of end pins, resting on fourpiers of granite masonry (numbered from east to west), at each end of whichare three 125 feet deck spans, the spans being separated by iron towers 25feet long, making the length of the iron structure at each end of the channelspans 425 feet. The end pins are placed 4 ft. 6 in. between centers over Piers II and III , and 3 ft. 6 in. between centers over Piers I and IV , and the endpin of the deck span is 1 ft. in. from the back of the bolster, thus makingthe entire length of the whole structure from end to end of iron or steel work,1993 feet 1 inch.

The bridge is built on a grade of 0.4 per cent. (21.12 ft. per mile) ascendingwestward. The clearance at the center of the east span was 53 feet above thewater of April 14, 1884, and that at the center of the west span 56 feet abovethe same high water, this stage of high water being about six feet below thehighest water observed except that of 1881; these clearances were both ac-cepted in the approval of the plans by the Secretary of War. The actualclearances above the extraordinary flood of 1881, so far as this can be deter-mined, are 43.5 and 46.5 feet respectively. Since the construction of thisbridge, a Standard High Water has been established by the Missouri RiverCommission at this place (circular of April 24, 1889); the clearances abovethis high water are 50.8 and 47.8 feet respectively.

'The east approach is 15,220 feet long from a connection with the trackbuilt by the St. Joseph & Nebraska R. R., in Section 36, T. 61 N., R. 40 W.,to the end of the iron work, the maximum grade on this approach being 0.5per cent. (26.4 ft. per mile.)

The west approach is 19,260 feet long from the west end of the ironwork to the connection with the Atchison & Nebraska R. R., the maximumgrades being 0.4 per cent. (21.12 ft. per mile) in each direction, excepting ashort piece of one per cent, put in temporarily at the connection.

Besides the two approaches proper, a third approach, called the Atchisonconnection, was built connecting the west approach with the old line of the

Atchison & Nebraska R. R., this connection being 1.36 miles long, with maxi-mum grades of 1.5 per cent. (79.2 ft. per mile).

Pier IV the west pier stands on the edge of the river bank which is 530feet distant from the base of the bluff, the intermediate ground being a pieceof bottom land of about the elevation of high water, but which is composed solargely of the tough soil known as gumbo, that the action of the river upon itis very slow. The only protection required was a quantity of riprap revet-ment at Pier IV and extending a moderate distance above and below; thisriprap must be carefully watched and may require extension sooner or later.

The only protection on the east side is the dike, which was the first workdone in the construction of the bridge, and which has acted admirably.

All the levels taken during the construction of the bridge were tied to thebenches established by the Missouri River Commission and referred to a tidewater datum, this datum being 412.71 feet below the St. Louis City Directrix.

III.

SUBSTRUCTURE.

The substructure comprises the four granite piers which support thechannel span and sixteen small cylindrical piers which support the towerswhich carry the deck spans. The principal piers are numbered from I to IV ,Pier I beginning at the east end. These four piers are built on pneumaticcaissons of the following dimensions:—

Pier

I,

S3

feet long, 25

feet wide

and 18

Pier

II,

55

iC

“ 27

(c u

“ 18

Pier

III,

55

(.

“ 2 7

u a

18

Pier

IV,

53

a

“ 2 5

a a

“ 3°

All caissons were built with a side batter of one in twenty-four.

The foundations were put in by the company’s own men under the direc-tion of the Resident Engineer. The masonry was built by contract by thefirm of Drake & Stratton.

The caisson for Pier I was built in a pit excavated on the dry sand baron the east side of the river. The caissons for Piers II and III were built inposition on pile false work and lowered with screws to the bottom of the river.The caisson for Pier IV was built in a pit excavated in the shore close to theriver.

The pneumatic machinery was purchased from the Missouri Valley &Blair Railway and Bridge Co., and was the same machinery that had beenused in sinking the foundations of the bridge at Blair crossing. ' The ma-chinery was first set up on the east side of the river near the site of Pier I.Subsequently all of the machinery was transferred to the steamer John Bertram,which was purchased from the Sioux City & Pacific R. R., having been builtto be used as a car transfer boat at Blair Crossing. This steamer arrived atRulo May 28, 1886, and when equipped with the full outfit of pneumatic ma-chinery, formed an admirable tool.

The caisson for Pier I was built ot pine with an iron cutting edge andplanked with two thicknesses of pine plank. The other caissons were builtin the same way, except that the iron cutting edges were made heavier and thelarge sill timbers were of oak.

The caisson for Pier I is surmounted by 53 feet of crib work built in threesections and stepped down to 46 feet by 18 feet at the top of the upper section.The caissons for Piers II and III are surmounted by 42 feet of crib work builtwith the same batter as the caissons, but with the corners cut off so as to makethe horizontal section that of an irregular octagon, the crib being sheathedwith oak plank and the corners plated with 3-8 inch iron.

The caisson for Pier IV is surmounted by 50 feet of crib work 48 feet by20 feet, the sides being plumb.

Both caissons and crib work were filled with Portland cement concrete.

The excavation of the pit for Pier I was begun December 3rd, 1885, theframing of the caisson December 14th and the setting up of the cutting edgeJanuary 15, 1886.

The caisson was finished February 13th and the concrete filling was begunFebruary 18th. Air pressure was put on P'ebruary 20th and on March 19th thecaisson reached the clay at elevation 792.1. After sinking about four feet intothe clay a test pit was begun March 30th and sunk 19.3 ft. through the firstclay into the gravel which separated the upper clay from the lower clay andwhich at the site of this pier was only 3.4 feet thick. No increase of air pres-sure was required during the sinking of this test pit until the gravel was reached,and then it became necessary to increase the pressure at once to the fullamount corresponding to the actual depth. This test pit showed the upperclay to be a perfectly homogeneous layer on which it was considered safe to foundPiers I and IV , while it was thought best to sink Piers II and III to the lowerclay. The test pit having served its purpose the excavation was filled up andthe sinking of the caisson was continued till April 5th when an elevation of785.88 was reached. The sealing of the working chamber was begun on the