LIX

JOINT TRACK ELEVATION AND DEPRESSION AT SIXTEENTH AND CLARK STREETS, CHICAGO.

G. W. VAUGHN, M. Am, Soc. C. E.*

As considerable interest has been manifested in this work by all classes of railroad men who were at all familiar with the complicated nature of the conditions under which it was undertaken, the following brief and necessarily incomplete account, detailing some of the difficulties and complexities under which it was carried out, may be of interest. The diagram on Fig. 553 will serve to make clear to you in some degree the network of tracks in the field under review between 15th and 16th streets, as they existed on the first of March last. The distance between those streets was about one thousand feet, and bunched together in that space and covered by a radius of three hundred feet were found one hundred and thirteen rigid crossing frogs, and near by were seven slip switches for the use of the various lines of tracks of the fifteen different railroads crossing here.

The roads within this field were the Lake Shore & Michigan Southern, with two main tracks and seven switching tracks; the Rock Island, with two main tracks and one switching track; the Chicago & Western Indiana, with four main tracks and thirteen switching tracks; the Santa Fe, with two main tracks and ten switching tracks; the Chicago, Madison & Northern, with two main track; the Chicago & Alton, with one switching track; and the St. Charles Air Line Railroad, having two main tracks owned and used jointly by the Illinois Central, the Michigan Central, the Chicago, Burlington & Quincy, and the Chicago & Northwestern Railroads. In addition to this the C. & W. I. Company's tracks were used by the Wabash, the Monon, the C. & E. I., the Erie and the Grand Trunk Companies; thus, counting the Illinois Central and Chicago, Madison & Northern as one road, the trains and transfers of fifteen different railroads were concentrated in this field of about five acres.

Thus it will be seen that there were fourteen main tracks and forty-two switching tracks and the traffic over them to be taken care of, to say nothing of the two lines of rails of the City Railway Company, which crossed thirteen of these main and switching tracks. It may be proper to note here also, that the records of the different lines show that during the month of March, 1898, five thousand cars and five hundred engines passed this point daily. The plan prepared by the Advisory Board of Engineers of the several railroads and finally adopted, provided that the tracks of the

*Engineer in charge, Joint Track Elevation and Depression Sixteenth and Clark streets.

Chicago & Western Indiana and the Sante Fe Companies should be depressed about nine feet, and that all other tracks in this field should be elevated about ten feet. It also provided that Clark street should be elevated and pass over the depressed tracks on a steel viaduct, and that in order to permit its south approach to pass under them the St. Charles Air Line tracks were to be moved south eighty-five feet and pass over Clark street on a steel bridge.

Mr. James Dun, Chief Engineer of the Atchison, Topeka & Santa Fe Railway Company, was chosen by the Advisory Board of Engineers to have general supervision of the work, and on the 14th of April a contract for the masonry was let to the Brownell Improvement Company and work under it was begun on the 24th. Owing to the necessity for keeping the traffic moving it was thought to be extremely difficult, if not impossible, to use derricks in handling stone; and after a careful study of the problem it was decided to use concrete for both the retaining walls and abutments. To this time all of the tracks were in their original position, and the only ground upon which walls were to be built, which was clear of tracks, was that for the retaining wall north of the proposed depressed tracks and west of the tracks of the Lake Shore and Rock Island roads, and even this was crossed by two tracks of the Air Line and two Y tracks of the Lake Shore.

Work was begun on the section of this wall lying between the Rock Island tracks and those of the Air Line; north of this section of wall was a short spur track running parallel with it, and after the excavation for the foundations of this section of about 240 feet were made this track was utilized for the concrete mixer and the cars carrying the cement, sand, and stone for immediate use. When this section of wall was completed, temporary bridges having been placed under the Rock Island and Lake Shore tracks, the excavation for the foundation of the abutment was made and the concrete put in place under these bridges to a height of about seven feet, where it was left awaiting the elevation of the tracks. The same course was pursued at the St. Charles Air Line tracks, and in fact at all of the abutments for the fourteen tracks which were to be elevated. In the meantime work was actively prosecuted in the moving of tracks and in the construction of new ones in order to clear the grounds to be occupied by walls and abutments, and at the same time to provide facilities for keeping the traffic moving. From this time forward this work became a large factor in the item of cost, as in most cases new tracks were constructed before the old ones could be abandoned. In this way short sections of the retaining walls were constructed in such places as could be most readily cleared of tracks, the dominant thought in the minds of those in charge of the work being that traffic must be kept moving.

In this manner all of the retaining walls adjacent to the tracks which were to be depressed were finally completed, and the foot

Fig. 555. Chicago and Western Indiana Tracks May 29th, 1898, before elevating. View from 16th Street looking northwest. Walls and Abutments of Concrete Masonry on the left. Concrete mixer at work on the right.