Evening star. [volume] (Washington, D.C.) 1854-1972, 1911-07-19
NEW WATER CONDUIT
Work Started on Repairs to
Cabin John Bridge.
TUNNEL OF CAST IRON
Huge Metal Pipe to Make Sure Of
No More Leakage.
N0 ST0PPAGE OF SERVICE
Reservoirs Below Bridge Will Sup
ply City When Water Is
Cut Of.

An interesting engineering project for
the improvement Of the District water
supply system is in process Of execution
by Col. Langfitt and his chief assistant,
Capt. Hannum, the engineers In charge
of government works in this vicinity. 1t
involves the construction of a cast iron
tunnel through the length of Cabin John
bridge and is designed mainly to prevent
leakage from the conduit at that point.
which in recent years, especially IN the
winter time had become SO extensive as
to materially affect the city water sup
ply.
The present tunnel over the bridge Is
lined with brick and cement and mas
served it's purpose WELL considering the
long time 1t has been in service. 1t IS
difficult to keep In good repair. however.
and leaks constantly. Finally 1t was
concluded that complete metal lining
was necessary to insure perfect flow OF
water and prevent possible deterioration
Of the masonry structure OF the bridge
itself. At its last previous session Con-
gress appropriated $4,000 for the pur-
pose and all the preliminaries for the
work have been arranged
Problems to Meet.
The construction of q metal tunnel is a
comparatively simple operation from an
engineering standpoint In the present in
stance however, it Is necessary to build
the tunnel over the bridge without inter
fering with the water service and also
without interfering with travel over the
bridge. That is made possible only by
storing an extra quantity of water In all
the reservoirs below the bridge periodi-
cally, and then emptying the conduit by
closing the gates at the intake at Great
Fails. BY this operation it is possible to
work in the tunnel over the bridge for
only thirty-six hours every week. At nrst
it was thought that sufficient water could
be stored to admit of a total suspension
of the flow Of water for forty-eight hours
each week. Practical tests demonstrated,
however, that the daily demands OF the
system would not justify cutting OF the
supply for more than thirty-six hours a
week.
Because of the necessity Of prosecuting
the work in the tunnel without interfer-
ence with the regular water supply, which
during the recent hot spell exceeded 6G,-
0000O0 gallons day, and not being able
to work continuously more than thirty
six hours IN every seven days, II will take
about five months time to complete the
tunnel.
To Be Built In Sections.
Under the approved project the existing
brick tunnel over the bridge, having an
internal diameter of nine feet, will be
lined throughout with iron castings built
in three-foot sections, from each abut-
ment OF the bridge, u distance of about
80 feet. complete working plant. In
Guiding derrick for handling the cast
ings. has been established near the east
end of the bridge and the interior OF the
brick tunnel has been prepared for the
installation of the metal sect. ons. A con-
tract for supplying 80 tons of these cast
ings has been awarded to the Camden iron
works of Camden, y. j.. at a cost Of
about $1,000 and ii is expected that about
twenty-five tons will be delivered in a
few days. The work of putting them In
position will be done by the regular Wash
ington aqueduct force in charge OF
foreman. Capt. Hannum will personally
supervise the construction.
While that work Is In progress advan-
tage will be taken of the periodic empty i.
ing of the conduit to make necessary re-
pairs to the conduit at its upper end.
near Great Falls. The engineers have re-
ported that the conduit after forty-seven
years service is in excellent condition
and that the brick lining Is almost inva-
riably strong and sound. There are. how
ever, several places near Great Falls
where the conduit was blasted through
solid rock. where no brick has ever been
placed The outline of the conduit at
these places is rough and irregular and
is considerably larger in sections than the
lined portions. which have an internal
diameter of nine feet.
Decay in Rock Sections.
The latest inspection showed that it is
only at the first of the unllned sections
near Great Falls and at the bridges and
cuiverts that any material deterioration
has occurred. The only considerable de-
cay of rock was found to be In section
about 400 feet in length between Great
Falls and waste weir No. /. and not far
from that weir. To guard against any
possible danger to the conduit by OBJ
struction from falling rocks it has been
arranged to line with cement all that
section of the waterway where there is
evidence of rock decay. The work will
be done this summer whenever the shut
ting off of the water at Great Falls per-
mits the workmen to go into the big con-
duit.