s 
BULLETIN 1486, TJ. S. DEPARTMENT OF AGRICULTURE 
«_EL-I8.0 
EL-30.0 
the piers was started, it was thought that the soil between eleva- 
tions — 30.0 and —50.0 would be such as to admit the penetration 
of piling for a sufficient distance to insure adequate lateral support. 
Figure 6 illustrates the condition expected. Instead of this formation, 
80 solid foundation material 
(cemented gravel) was en- 
countered at elevation 
— 30.0, and owing to the 
fact that the superimposed 
load was a moving one, it 
was considered the part of 
prudence to redesign the 
foundation to insure maxi- 
mum lateral stability. 
After several tentative re- 
designs had been prepared, 
the scheme shown in Figure 
7 was finally adopted as the 
cheapest possible solution. 
This method of construc- 
tion utilized seven steel 
tubes carried to solid rock 
and filled with concrete, as 
shown in Figure 7. The 
following is a comparison 
of cost for the two types of 
foundation. 
Scheme No. 1. — (Possible 
if stiff clay had been en- 
countered at elevation — 30.0.) Total weight of structure above eleva- 
tion — 18.0, 1,348.75 tons. Number of piles necessary at 15 tons per 
1 348.75 
pile, ' -, J — =90. Assuming a penetration to elevation —50.0, the 
total quantity of piling needed would be 90 X 34 = 3,060 lineal feet, and 
at 40 cents per foot the cost would be $1,224. 
Scheme No. 2. — (Possible for soft rock or hardpan at elevation 
— 30.0.) Total area of base needed at 10 tons per square foot unit 
load would be 134.8 square feet. 
Six tubes with 43^-foot diameter and one central tube with a 
7-foot diameter give a combined area of 
Fig. 7.— Redesign of pier for swing span over Coquille River 
necessitated by encountering solid foundation at elevation 
—30.0. This design cost considerably more than the first 
design in which it was anticipated that piles could be driven. 
(4.5) 2 tt 
4 
(7.0) 2 7T 
X6 = 95.5 
= 38.4 
133.9 square feet. 
The following is the actual cost of the work constructed as indi- 
cated in Figure 7 : 
Steel tubular caissons in place 22,980 pounds, at 9 cents $2, 068. 20 
Excavation in tubes, 59.5 cubic yards, at $6 357. 00 
Concrete in tubes, 55.33 cubic yards, at $25 1, 383. 25 
3, 808. 45 
