The Coconino sun., 1924-05-02
THE CoCoNYNO SUN

ed with pockeLkn1Ie, or could De
pinched out with the fingers.
From the observations made at
that time. it was our opinion and con-
Cured in by Mr.. Davenport and Mr..
Proctor, that it was questionable
whether the material would be imper-
vious to head of water over 40 or
so feet in depth, and that the ma
terial was not suitable for any type
of masonry dam where the foundation
pressures would exceed five tons per
square foot. The indications in the
nit filled with water showed that the
material is more or less porous and
with a constant head Of water over
the formation it will become saturat-
ed or moist and this condition would
be classed similar, for clay in thick
beds moderately dry which the most
eminent authorities allow from four
| to six tons per square foot.
It was our opinion that the material
limited the height Of a dam to not
more than so feet and the type should
be one of a wide foundation of the
gravity masonry type, or earthern or
rockfilIed type of dam.
The semi gravity arch type is not
adaptable, as the same formation ex-
lists in the canyon sides, so that very
little thrust can be taken on the sides.
The multiple arch dam would not
he suitable for this material as
| foundation.
A recent article in the Proceedings
Of the American Society of Civil En-
gineers. August, 1928, by Fred A.
Noetzli on "Improved Type of Multi
ple Arm Dams," states that the gem
eral considerations are:
"Foundation - 1t is essential that
the foundation of multiple arch dam
be impervious by nature, or we made
so by prouting, or by deep cut-off
trenches, in order to prevent water
from percolating below the arches
and starting erosion. One must also
he assured Of the bearing value OF
the material under the butresses, so
that no irregular settlement will oc--
cur. The arches and butresses OF
high multiple arch dams should be
founded on and keyed into solid rock
so as to provide safety against slld-
mo between masonry and foundation.
/ In this same article, under the para.
oranh of "Factor of Safety of Dams,
! IS the following:
"The stability of most engineering
structures depends on two dlstlnct
factors: First, the adequacy ana saIe-
tv of the material Of the foundation
and the nature of the contact between
this material and the structure; and
second. the stresses in the structure
due to its weight and the loads and
other influences which may be acting
unon it For example, dam built
upon an inedaquate foundation may
he doomed to failure notwithstanding
that perhaps the structure itself was
of a conservative design, with low
nnit stresses in the masonry"
sI+ is one of the great advantages
of multiple arch dams that the danger
of uplift is practically ellmlnated'
Furthermore, any sliding between
buttresses and foundation may be pre-
vented by excavating for the but
tresses substantial trenches OF SUIT
able depth extending into sound bed
rock and embedding the buttress FOOT
ings securely in such trenches.
In the case of any masonry type OF
dam the foundation is the all lmpor-
tant factor and in this particular case
where no firm bedrock has been en-
countered, it is a question for the
0eologist and chemist to determine
the characteristics of the material.
Samples of the material collected
by c.. T. Pulliam, city clerk, at oui
reuuest. were submitted to Prof. "
r Tolman of Stanford university, for
examination and report. Prof. Tol-
man was formerly state geolog1st OF
Arizona and is personally familiar
with the general geological conditions
ovar the state. Prof. Tolman classl-
fled the material as strictly volcanic
denosit of tufacious character WITT
very little or any calcareous SUD
stances that would be of a cementme
nature. The finer particles separat
ed when immersed in water In tes'
t1lbe and would, therefore, be readily
carried away with any slight fioW o
velocity of water through tne ma
terial. Prof. Tolman was very DOUBT
ful of the material and formation 10
the purpose of reservoir and dam
I and without a more extensive stud!
of the geological structure on tne slt'
and surrounding vicinity, could no
recommend the construction of dan
and reservoir on this material.
We also consulted with Prof. G. I
] Wing. dean of the engineering de
partment of Stanford university, an
professor of structural engineering
as to the feasibility of various type
of dams on this material and location
Prof. Wing stated that a rock-fill Q
earth dam of moderate height wit
: deep cutoff walls into the STRAIT
would be the most satisfactory. 1
. gravity masonry type with deep cut
off walls and design of foundation
: to keep within the bearing capacity o
the material would also be safe, bu
any thin arch dam would not be safe
81 Mr.. Davenport obtained the follow
ing information from the director o
! the u. S. geological survey, Wash
. ington, D. c.:
]. aMr. Darton, one Of the geologist
81 of this survey, who is familiar wit
q the San Francisco volcanic field, give
= the following information regardin
IL law CabnI