The Evening critic., 1884-05-23
A DOUBTFUL DAM.
Some Engineering Difficulties at the
New Reservoir.


The work on the dam OF tho new reservoir
which has been pushed with grott energy by
tho contractors since tho opening OF spring,
has now reached point where decision
OF great deal OF Importance must be made by
tho engineer In charge. Th' Importance of
this decision was foreshadowed by discussions
in THE CRITIC at the lime tho plans and esti.
mates for the work were being discussed
three years ago. At that time there was quite
a controversy In engineering circles over the
points that must now be decided, and suSh
authorities as General Meigs and Colonsl
Thomas Lincoln Casey woro found dissenting
from some OF the conclusions OF the District
Engineers.
The Question mt Issue
related TO the method OF secur-
ing the body of tho dam against the
effects Of saturation aud consequent
weakening or possible destruction by the
"stepago" OF tho numerous springs which
were known to belong TO the GROUND upon
which IL was to be built. Tho plan adopted
by the District engineers was that OF q simple
entthwofk dam, with no protection against
the burrowing tendencies OF su bjacent springs,
except such as might be Afforded by what is
known Ms "core" OF puddled clay.
This device General Meigs and Colonel Casey
pronounced insufficient because OF the pscu-
liar character OF the ground on which the dam
was TO rest. These eminent engineers pointed
out that the ground upon which the dam was
TO be built was formed by the slopes OF a basin
which was the head OF a living stream, and as
Permeated with spriBgheads and
Undermined by Belts of quick
sand.
They held upon such foundation the tom
dency of a purely earthwork dam would be to
receive saturntion from the water proceeding
from these springs, which would gradually
burrow passages through It ana thus grad
ually undermine the structure. Tho maxi
man head OF water In the reservoir being
over thirty feet constant pressure would be
exerted calculated to aid the natural efforts OF
the springheads to ind outlet.
The ultimate result OF the operation Of
these forces, II was believed, would DO TO
cause necessity for frequent repairs, which In
the long run would BIO far moro expensive
than properly constructed dam in the nrst
instance would be; not TO mention the possi-
bility OF the dam giving way altogether and
destroying everything in the valley from the
reservoir TO the canal. This danger was not
any weakening that might be caused by sat-
uration would probably be discovered before
tho dam could give way; so that the expert.
ences OF the Croton dam In 1871, and the
Worcester dams In later years were not likely
TO be repeated here.
But whenever Weakening Was Dis.
covered
II would be necessary to empty the reservoir
In order TO repair the dam, thereby suspend
ing for a time the water supply derived from
II, the inconvenience OF which must DO reck.
oned In addition to the cost OF repair.
On these and other more technical grounds
General Meigs and Colonel Casey insisted that
the dam ought, in the first instance, to DO
cored throughout with solid mass OF con.
crete or masonry, impervious to water, and
that in making It's foundation the utmost care
should be exercised to excavate all the beds of
quicksand that were known to exist along the
lower slopes OF the hillsides and in tho bed of
the rivulet that headed In the basin.
These views were not adopted by tho Dis
trict engineers, but loss thorough, though
on. The result Is that as the excavation has
proceeded the engineers In charge
Have Encountered Creator Dim-
cuIties Than They Anticipated
until within few days "a temporary halt has
been called until more critical examination
can be mnde. The matter will, 1t is under
stood, receive the attention OF General New
ton himself as the work, though nominally in
Congress imposed upon the Engineer Bureau
ofthe War Department, and tho Chief Engl-
neer OF the Army is therefore ultimately re.
What a Contractor Snid.
Thinking that perhaps some further In.
formation might be obtained at the scene OF
operations a CRITIC reporter this morning
called upon the managing member OF the flrm
OF contractors who are doing the work and In.
terrogated him upon tho points involved. This
gentleman stated, with smile, that he had
done too much work under the superintend-
ency OF military engineers to be guilty OF such
thing AS expressing an opinion OF his own
upon any subject involving professional eti.
| quette.
| tin this work." said he, "all have to do is
| TO conform to the specifications OF tho con-
| tract, and for the rest obey orders the same as
| private soldier. II the engineers In charge,
| from Lieutenant Symonds up to General New.
| ton ask my We've, shall give them, together
| with the results of my experience, which
1 covers over thirty years of constant occupation
| In hydraulic work. But l do not deem It
| proper to enter Into any controversy that may
be going on
II is said that General Newton, who takes an
active interest In this work, is inclined to &C.
cord great weight to the Views OF General
| Melgs, who Is regarded rs tho founder of tho
| present system OF water works, aud whose
| work ON the old aqueduct and the reservoirs
| above Georgetown forms one OF the monu-
ments OF the Capital City.