Fergus County argus. [volume] (Lewistown, Mont.) 1886-1946, 1906-04-17
Earthquakes and Dam Construction.

Earthquakes and Dam Construction.
An important question affecting the
choice of the type of canal to be built
at Panama is that of the possibility
of seismic disturbances and their
probable effect upon the canal. I'm
like the Nicaragua district, Panama
is practically free from earthquakes
of any magnitude; and the indications
, are that this comparative immunity
has existed for a long period. The
fact was brought out during the re-
cent examination into conditions at
Panama by the senate committee, that
there exists in an ancient church in
the canal zone, a masonry arch, which
is so fiat that by all the laws of equi-
librium it should long ago have fallen
in. 1t is an object of great curiosity
among our engineers on the isthmus,
one of whom admitted in the senate
inquiry that he was at loss to un-
derstand how a structure, so evident
ly near the breaking point, should
have maintained it's stability for hun
dreds of years. Now this engineering
phenomenon is taken, and very proper
ly so, as giving unmistakable evil
dence that for several centuries Pan
ANA must have been free from these
more serious seismic commissions
which have wrought such havoc with
structures of every kind in other
countries of Central America.
At the same time, it is known that
Panama is not altogether free from
earthquake tremors, and in making
our choice between a high-level and
a sea-level canal, the possible destruc-
tive effects of earthquake disturban-
ces upon the dams and locks of eth
err type must be taken into considera-
ton. Unquestionably the most vul-
nerable point in either type of canal
will be the dams, for upon them will
the very existence Of the canal de-
pend A sea-level canal would in
volve the construction at Gamboa of
a masonry dam 1856 feet high, besides
several smaller dams to control the
flow of small streams tributary to
the Chagres. A lock canal calls for
the construction at Gatun of an earth
dam 1876 feet high. The masonry dam
at Gamboa will consist of solid wall
carried down everywhere to rock
foundation and varying in thickness
from 100 feet at the base to 80 feet
at the water level. The earth dam
at Gatun will consist of a mass of
closely-compacted sand and clay, q
SEQ feet thick at the base, and 375
feet thick at the water level. AS far
as We know there are no actual data
to go upon in considering the ques-
ton of the relative effects of an earth
quake upon masonry and earth dams
but it is surely reasonable to expect
that under the tremor of an earth
quake the lofty, comparatively thin,
and unyielding masonry wall of the
Gamboa dam would be more likely to
rupture than would the broad and
more or less elastic mass of the Ga
tun earth dam; particularly when we
be practically dry throughout its
whole mass, while the earth dam will
be more or less saturated and plastic.
Furthermore, crack in dry so foot
masonry wall would be more likely
. to extend entirely through the mass
than it would if it occurred in a great
earthen mound, whose average thick
ness was over thousand feet.
, We are free to admit that when
) this question is considered in it's bear
!. ing on the masonry locks, the ad
, vantage lies with the sea-level canal
r which has but one of these. At the
same time, a crack through the walls
! of lock chamber would not be com
. parable in the extent of the delay. OF
. the possibility Of disaster, to frac
, ture of the great dam at Gamboa
2 Failure of that dam would mean the
r. wrecking of the whole CANAL but the
/; failure of lock chamber would moi
}. necessarily mean even an interruption
j. of navigation. For the locks will be
a built in duplicate, side by side; and
o unless the damage extended entirely
across the whole system, ships could
S cross through the uninjured lock while
= the damage was being repaired. Ev
en- if the damage extended entirely
d across both flights of locks, it is no
+. likely that the whole of the SUNNI
'. water supply would be lost, as i
k would be- We're the Gamboa dam de
y stroyed; for the lock gates would
y serve to hold back the impoundet
t. waters until repairs had been made
d and the repairs would not involve
/, anything more serious than groutini
o out the crack with cement
5. However, in any discussion of tn,
y earthquake problem at Panama. w,
e must be guided by probabilities, an,
l. these indicate that the risk from
e earthquakes is extremely slight. il
/ indeed, it may be said TO exist at al
S Were the canal zone known to b