HIGHWAY BRIDGE LOCATION 7 
for judging the relative merits of different conditions, these being 
to a large degree modified by the nature of the individual problem. 
The following brief discussion of the most frequently encountered 
foundations may, however, prove enlightening as far as general prin- 
ciples are concerned. This discussion does not apply to deep foun- 
dation work employing compressed air or open dredging to great 
depths, but only to the foundation conditions ordinarily encoun- 
tered in ordinary highway bridge practice. 
TYPE A. EXPOSED SOLID ROCK OF SATISFACTORY QUALITY 
This is without question the most satisfactory, certain, and cheap 
foundation condition which can be obtained. Plate 1, C shows an 
example where advantage has been taken of foundations of this 
character in the bridge location. 
TYPE B. SUBAQUEOUS SOLID ROCK 
ROLLER TRACK ANO RACK 
EL.-I8.0 — x 
EL.-30.C ^* 
SAND ANO CLAY 
EL.- 50.0 5TIFF 
OftlVING S0IL-y_ 
-EL. + 25.92 
EL. + 4-0 AVERAGE 
CONSTRUCTION STAGE 
_0 AT U M_ LJN E EL . 0. 
(MEAN LOW WATER) 
^- EL- 8.0 
■EL.-I6.0 CUT-OFF 
The idea seems to have gained prevalence, especially among those 
who have had little actual construction experience, that any solid 
rock foundation is to be 
preferred to softer ma- 
terial at the same depth. 
This, however, is far from 
true, in fact, for sub- 
aqueous work, the pres- 
ence of solid rock under 
certain conditions may 
entail an expense much 
greater than if a reason- 
ably stiff clay were en- 
countered at the same 
depth. This point is 
illustrated by Figure 6, 
which is a sketch showing 
the principal dimensions 
of the center pier for a 
239-foot steel-draw span, 
built over the Coquille 
River under the writer's 
direction, in 1921. 
The original plan con- 
templated the driving of 
timber piles below eleva- 
tion — 18.0 as shown. 
The bid price on piling 
was 40 cents per lineal 
foot in place. The total 
weight of the center pier 
and superstructure rest- 
ing thereon was 1,348.75 
tons. From elevation 
- 18.0 to elevation -30.0 
the soil encountered was a sand-clay mixture with insufficient 
resistance to afford lateral stability to piling. When the work on 
Fig. 6.— Details of first design of pier for swing span over the 
Coquille River showing foundation conditions expected 
