34 
The Colorado Experiment Station. 
made. Larger rocks may be used in the footing than in the wall 
above. 
Fig. 2 shows the manner in which a trench may be dug around 
the bottom of the excavation and filled with concrete to form the 
footing. It also shows the manner in which the surface of the foot¬ 
ing may be leveled by resting one end of a straight edge board upon 
a center stake and the other end upon the surface of the footing. 
When the inside form is set up it rests upon this footing. The 
form is so constructed that when set upon a level base the sides will 
be plumb. Hence if the footing is not level, the wall of the silo will 
not be started plumb and difficulty will follow. 
Figure 3 shows a cross section of the silo wall and footing- 
after the inside form has been set upon the footing and the six- 
inch space between the form and the dirt wall has been filled with 
concrete. It will be seen from this cut what the effect of an irreg¬ 
ular dirt wall would be. 
Excavating in Loose Sandy Soil. —In case the soil is such that 
the walls of the excavation cave and give way it will be necessary 
to excavate from a circle considerably larger than the silo so that 
the outside form may be set up around the inside form to take the 
place of the dirt wall. The footing in this case will be made by 
digging a trench, about two feet wide and from one to one and a 
half feet deep and filling it with concrete. The footing should be 
laid out so that the silo wall may be started upon the center of it. 
This may be done by describing two circles in the manner shown in 
Fig. i. The circles should be separated by a, distance equal to the 
desired width of the footing. 
Reinforcing Foundation. —The foundation should be well re¬ 
inforced. This may be done by laying strands of barb wire three or 
four inches apart in the concrete as the trench is being filled. 
Reinforcing Wall Under Ground. —The wall under ground 
should be reinforced in the same manner and with the same woven 
wire that is used above the ground. 
Setting Up Forms. —At the first setting, the inside form rests 
upon the footing. The diameter of the inside form should be taken 
after it is set up and in case it has been forced out of circle shape 
it should be drawn back again. 
After the forms have been filled and allowed to set over night, 
they are ready to be raised for the first; time. Before this is done 
the scaffolding must be started. 
Scaffolding. —Proper scaffolding is a very important feature 
of concrete silo building. No outside scaffolding is used. An idea 
of the scaffolding arrangement can be gained by reference to cuts 
