|A Chicago Tunnel Railway electric locomotive.|
Sixty miles of tunnels are being constructed under the principal streets of Chicago. Twenty-six miles have already been completed. Over a narrow gauge electric railway in these conduits the Illinois Tunnel Company expects to transport 90,000 tons of freight daily after January 1, when it hopes to begin operations.
So quietly has the work been carried out, with no interruption to traffic and no obstructions in the streets, that only a small percentage of Chicago's population is aware of the scope of the enterprise, or of the fact that the business district will be honeycombed with shafts, leading to all of the railroad stations and to the principal mercantile establishments.
Under an ordinance granted by the City of Chicago on February 20th, 1899, the Illinois Telephone and Telegraph Company -- a new corporation -- was given a franchise for the use of space under the streets. It constructed a network of large tunnels beneath the business district, with roofs not less than twenty-four feet from the surface. These tunnels are of two sizes, the trunk conduits being twelve feet wide and fourteen feet high and the branch shafts six feet wide and seven feet six inches high. The material is cement, which in the larger tunnels is twenty-one inches thick at the bottoms and eighteen inches at the walls.
Under the roof and along the walls of the tunnels on each side are strung the telephone cables, leaving space on the floor sufficient for a railway. The company in July, 1903, therefore secured an extension of its franchise rights, permitting it to operate apparatus for carrying freight of all kinds and for handling mail matter, packages, newspapers and other articles. The Illinois Tunnel Company last January acquired the system.
More than two miles of twenty-four inch railway already have been built, and this mileage rapidly will be increased until all the shafts have been equipped. Over these rails will run trains drawn by electric locomotives, now in successful operation. The cars are wholly of iron and steel and are twelve feet in length.
Each will have a capacity of thirty thousand pounds of freight. The trolley system of propulsion is being used, driving the trains at a speed of from fifteen to twenty miles an hour. A five thousand horse-power electric plant soon will be in operation.
Upon the completion of the track laying, three thousand cars and one hundred and fifty locomotives will be put in service. These will run to the six great freight depots of the twenty-five trunk railroads which center in Chicago. All of the stations are within a section less than two miles square, and the enormous freight traffic of the city has caused congestion in the streets. The tunnels will relieve this, as they are expected to take as a single step nearly all of the four million tons of coal burned annually within the "loop" -- the elevated railway marking the center of the business district.
The system of handling the freight will be simple. Shafts are being constructed from the tunnels directly into the freight houses of the railways, and the tunnel cars will be lifted on elevators to the sides of the freight cars ready to be unloaded. When the underground car is filled it will be dropped again into the tunnel, ready to be unloaded at the warehouse of the consignee or placed in the Tunnel Company's storage quarters to await his orders.
Nearly every large business house in downtown Chicago will have shaft connections with the tunnel system, elevators like those at the freight depots carrying the cars into the stores or storage houses. As the tunnel cars will accommodate any object that can be passed through the door of any railway freight car, there hardly is anything which the Tunnel Company cannot transport to the merchants.
The installation of this system will remove thousands of wagons from the downtown streets, keep them cleaner, and make the handling of freight much cheaper than it is at present. Chicago is the only city in the world to employ an extensive system of this kind, and the effect of its successful operation will be incalculable. There is little doubt that New York, with its subway for the transportation of passengers, will follow with its tunnels for the hauling of freight, and other crowded cities cannot but profit from the change from old to modern methods.
A feature of the tunnel system is the great distributing station at the river and Taylor Street. The Tunnel Company a few months ago purchased for nearly $2,000,000 seven large warehouses for use as its terminals. All freight not immediately desired by the consignee, and all of which must be re-routed, will be shipped to this center. All the trunk lines of the tunnel meet here, and the cars can be elevated to the tops of the seven-story building and unloaded there. Merchants buying in large quantities save great sums, and fall, summer, winter and spring stocks often begin to arrive months before they are placed on sale. The larger merchants have their own warehouses for the storage of these goods, and shafts will extend to their warehouses. The smaller dealers, however, generally are deterred from purchasing in advance because they lack room in which to place their stock. Under the new system this may be stored in the Tunnel Company's houses and taken out in small lots, just as the retailer desires it.
The ultimate intention is to extend the tunnels into the manufacturing districts, and far away from the business section. Not until the downtown system has been put in successful operation, however, will the tunnels be dug further than present plans provide. The work now on hand is to connect them with the freight depots and basements of buildings.
The construction of the tunnels has been an enormous undertaking. Work was begun in an alley near Madison and Monroe Streets, west of La Salle Street. Seven other shafts were started at various places in the downtown district. It then was found that the city street maps were inaccurate, and a complete new topographical survey was made. The pneumatic system was used in the excavating. Airlocks were placed just inside the several shafts and air under pressure was admitted into the portion where the men were working. The shafts were made larger than the dimensions of the finished tubes, allowing a space of nearly two feet at the sides. Iron ribs were placed at short intervals along the inside, and within these were built walls of wood. In the space between the inner and outer walls, cement, stone and gravel were poured, making a solid mass that would uphold all weights in the roadways above. Another system of false work used was that in which steel plates were placed to support the cement while it was drying and to permit the workmen to tamp it down firmly.
The work was carried on by three shifts of men laboring eight hours each. The first gang of miners went on duty at 4 o'clock in the afternoon and worked until midnight; the second labored from midnight to 8 o'clock in the morning, and the third, which was known as the concreting shift, began at 8 o'clock in the morning and worked until through. The last completed their tasks so the miners could resume work at 4 p.m.
The distance excavated by the two shifts of miners averaged twenty-one feet at each heading. The number of headings was around fourteen. It required twenty men to operate each heading, and 850 were engaged in tunnel construction, while 600 others were employed in the offices and in hauling gravel, stone, cement and excavated material. Nine hundred tram cars were used in removing the dirt, which was taken out at the rate of more than 400 running feet a day. The cars were hoisted up the shafts to the elevated houses a few feet above the street, and from these the dirt and stone fell into wagons beneath. The dirt then was hauled to the lake front, where it was used in increasing the size of a city park. Later the method was changed by having a tunnel extended directly to the lake front, removing the necessity of teams for hauling the filling. At another end of the system the cars were run out upon scows and the clay taken down the river. It is estimated that more than 4,950,000 cubic feet of dirt have been excavated.
The Illinois Tunnel Company has an authorized capital of $30,000,000 and a bond issue of the same amount. It has issued only $15,000,000 of the bonds, however, holding the remainder to pay for future extensions of the tunnels and of the transportation and telephone systems. The officers of the company are: President, Albert G. Wheeler, of Chicago ; Vice-President, C. D. Simpson, of Scranton, Pa.; Secretary, Edward W. Gearhart, Scranton; Treasurer, John C. Law, of Pittsburg, Pa.
The Chicago Tunnel Company has in progress several extensions to its system of freight tunnels under the business section of the city. These extensions include several branches from the main lines under streets to the subbasements of large buildings being constructed, one extension in Canal St., from Taylor St. south to the new freight station of the Minneapolis, St. Paul & Sault Ste. Marie Ry. Line and another on 13th St., from Indiana Ave. to Lake Michigan, where a new disposal station will be placed. At this disposal station cars of excavated material from various parts of the business district will be lifted by two elevators and the spoil will be used to fill in along the lake shore. The disposal station is provided by the Chicago Tunnel Co. as a convenient means of disposing of waste material. The land which will be filled in is a part of a project of the South Park Commission to extend Grant Park along the lake front.
The length of the tunnel extending from Indiana avenue to the Lake on 13th St. is approximately 1,000 ft. It is 6 1/2 ft. wide and 7 ft. high with an arch built to a 3 ft. 3 in. radius. The tunnel extension is carried for almost all of its length, under the right of way of the Illinois Central R. R., and the material excavated is a soft blue clay which is easily cut with a draw knife. Air pressure is used on this extension because of the soft nature of the clay and because of the location of the tunnel under the right of way of the railway. A pressure of 10 lbs. is carried. The railway company has a compressed air plant at this location and carries an air pressure of 100 lbs. for use in the coach yard. Air from this plant is furnished for the tunnel work. The air pressure is supplied through a reducing valve which automatically maintains the pressure in the tunnel at 10 lbs. For emergencies a motor driven compressor is installed in the tunnel.
Three shifts are worked in driving the tunnel and each shift excavates and lines 6 ft. of tunnel. The first 4 1/2 hours of the shift are occupied by mining. Two miners cut away the heading and two muckers load the chunks of clay -- which come out in pieces of the consistency of putty -- onto small cars which hold about 6 cu. ft. These cars are passed through the air lock and hauled away in trains through the main tunnel to a disposal station. There are about 13 cu. yds. of excavation in the 6 ft. section of tunnel. Two men excavate this and throw the material back to be loaded in cars by the two helpers, in about 4 1/2 hours, or at the rate of 0.7 cu. yds. per man per hour.
After the excavation is completed about four batches of concrete are thrown in the bottom and leveled off approximately to the elevation of the bottom of the ties in the permanent track work. Two or three planks are laid on this to support the steel ribs for the forms of wood lagging and these ribs are bolted together in place. The ribs consist of 6-in. channels made to conform to the shape of the tunnel. They are in two pieces with flanges at the top and bottom so that they may be bolted together. A 1-in. wood block is placed between the flanges so that the bolts pass through the block. When the ribs are removed this block is first knocked out so that the steel ribs may not bind. The flanges for the bolts which tie the two sections of the rib together are not made square with the rib but are skewed about 10°. This provision aids materially in loosening the ribs when they are unbolted.
When the ribs are set up and bolted in position 3 ft. apart, a piece of 1 3/4x6 in. lagging is placed behind them on each side of the tunnel and held there by driving a nail through the steel rib. Holes in the ribs are provided for this purpose. Concreting then is commenced and the lagging is placed on each side as fast as the concrete is carried up.
The concrete is brought into the tunnel through the lock in the same cars used for carrying out muck. From 31 to 35 one-bag batches of 1 to 5 bank run gravel concrete are used for each 6-ft. section of tunnel. The gravel is brought to the work in canvas bags holding about one bushel each. The concrete is hand mixed outside the lock. The mixture is made sufficiently wet to cause the cement to set but is not wet enough to form a sloppy concrete. In the arch or key, 3-ft. lagging instead of 6 ft. is used and the concrete is put in over the end of the 3-ft. lagging and rammed back to fill the space. The last concrete placed in the key is sloped back to the roof so that it will form a sloping joint with the next section.
Concrete is allowed to set at least four days before removing the forms and lagging in sufficient amount to permit the continuous prosecution of the work is provided. This requires 72 lin. ft. of forms.
The work of extending the Canal St. tunnel is being prosecuted without air pressure. This tunnel is approximately the same size as the 13th St. extension, but is oval in shape, corresponding to the standard section of tunnels under the city streets. The Canal St. excavation is more difficult, and grub hoes and matlocks are used to cut down the heading. Six men form a gang and three shifts of eight hours each are worked. In each shift 4 lin. ft. of tunnel are excavated and lined.
Following the work of extending the tunnel as described, the narrow gage track is laid and concreted in, and the tunnel is plastered with a mixture of 2 parts stone dust and 1 part cement. The stone dust is ground limestone and the mixture adheres well to the rough surface of the concrete. It produces a smooth surface and waterproofs the wall satisfactorily.
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Last updated 01-March-2010