ASAE GH OLOGISIs 164 
of the Black Lick retaining wall. The steel ribs were spaced 4 feet apart 
throughout the wall and connected with 2 by 2 inch angle irons running 
horizontally through the mass as shown in the figure. 
TUNNELS, 
Reinforced concrete is used very often for the lining of tunnels. It 
is very similar, in general, to the lining of plain concrete heretofore 
described, its chief advantage being in unstable soils or in soft or strati- 
fied rock where falls or squeezes occur. Here the steel bars or members 
aid in supporting the pressure until the concrete has become perfectly set 
and also supply the tension members which aid the lining to withstand 
distortion. 
Tunnel Under River Spree, Berlin.—A notable example of the use 
of steel concrete is in the tunnel under the River Spree at Berlin, Ger- 
many. It is 2,017 feet long and lies 40 feet below the level of the river. 
It is formed of a cast steel cylinder, 13.12 feet in diameter made into 
rings, set together and covered with 3% inches of cement mortar upon 
the outside, and 434 inches upon the inside, with a heavy concrete floor. 
The steel rings vary from 1.64 to 2.13 feet in width. 
SEWERS. 
There are many forms of steel concrete used in sewer work. Ex- 
panded metal has been frequently used, being imbedded in concrete either 
just over the arch, or encircling the entire barrel. 
Plain round and square bars, angle irons, I-beams and the Monier 
wire mesh have been used under various conditions. 
One system that is being extensively used in Cleveland and Colum- 
bus, Ohio, will be briefly described here. It is known as the Parmley 
patent. 
It consists of a system of two sets of round or flat steel bars im- 
bedded in the concrete. The sets are staggered, one set being placed 
near the inner lining of the sewer, while the other set is near the outer 
side of the concrete walls. Both sets, however, are kept close to the inner 
surface of the crown of the arch and only extend downward to a point 
about one-fifth the diameter of the sewer below the center line. Longi- 
tudinal rods are also used to aid in distributing the stresses. To over- 
come the disadvantage of having the bars continuously in the way during 
the construction of the invert, the bars are cut into pieces and either 
punched for bolting or bent to engage hook and eye fashion. The shorter 
pieces are set into the concrete vertically, extending above and below the 
spring line, the arched piece being set in place when everything is ready 
to concrete the arch. For smaller sewers, the iron or steel rods, which are 
small, can be brought upon the work in merchantable lengths and cut 
and bent cver forms as the work progresses. 
