106 ANNUAL REPORT 
concrete composed of I part of cement, 2 parts of sand and a parts of 
broken stone. The portal head walls were of 1 part of cement, 3 sand 
and 6 broken stone. Figures 50 and 51 show south portal and section 
of the Peekskill tunnel. 
Chicago Telephone Tunnels,—Perhaps one of the largest, at any 
rate one of the longest, tunnels ever attempted is that of the Illinois Tele- 
phone and Telegraph Company in Chicago. The trunk tunnels are 
1234 by 14 feet and the lateral tunnels 6 by 714 feet in the clear. Their 
total length when completed will be about sixty miles. Up to September 
I, 1902, twelve miles had been constructed and the work was advancing 
in fourteen headings at an average rate of 328 feet per day for com- 
pleted work. About 1,500 men were employed in three shifts working 
eight hours each. The crown of the tunnel varies from 24% feet to 35 
feet below the surface of the street. The tunnel is being driven through 
stiff, blue clay without any support being required. Semi-circular draw 
knives are being used to cut down the clay. It is then shoveled into 
the cars which transfer it to the shafts where it is lifted to the street 
above. ~The “mbs used! for, the) forms) are of channel irony. 2) ineh 
channels for the laterals and 5 inch channels for the trunk tunnels. 
Two inch planks are used for lagging. The concrete consists of 1 
part Portland cement and 5 parts crushed limestone, screenings and stone 
below 34 inch in size being used, or gravel and sand being used in place 
of crushed stone. At curves and intersections, the concrete is strength- 
ened by being made in proportions of 1 cement to 4 of stone or gravel. 
The floor is first put in place, the ribs are then set up and braced and 
the lagging suspended upon the frame work of ribs. The concrete is 
rammed behind the forms in layers and as each layer is finished, lagging 
is added until the key of the arch is reached—here short lagging is 
used and the concrete rammed into place from the end of the wall. After 
the forms are removed the walls are plastered to make them smooth 
and impervious. ‘The floors of the trunk tunnels are 21 inches thick, with 
side walls 18 inches thick, while in the laterals the floors are 13 inches 
thick with 10 inch side walls. In the twelve miles of work done, 175,000 
cubic yards of excavation have been removed and 90,000 barrels of cement 
have been used in the work. The tunnel was kept in most scrupulous 
cleanliness by the superintendent. The writer was never in a cleaner 
tunnel in his life. One could travel miles through the tunnel, going right 
into the working headings, and not soil a dress-suit nor injure patent 
leathers. At every street intersection street name plates are set into the 
concrete walls so that it is much easier to determine one’s location in the 
tunnel than in the streets of the city above. Figures 52, 53 and 54, show 
a section of the completed tunnel, one of the ribbed forms for the trunk 
tunnel showing method of bracing the forms and a completed intersection. 
Figure 53 also shows the diaphragm plates used at the end of a section to 
pkeephtherconcrete im place: 
