Evening public ledger. [volume] (Philadelphia [Pa.]) 1914-1942, 1915-08-27
ENGINEERING PROBLEM
TO KEEP SUBWAY FREE
OF WATER AND GASES
n;aiculties Arise at City Hall
Where the Tube Will Dip
Considerably Lower Than
It's Normal Depth
rsrTMPS" FOR DRAINAGE

r,.o Of the most important problems
.sronting the engineers in the con-
.-,c,ion of the Broad street subway
s.r CITY Hall will be the drainage
nd the proper ventilation of the tube.
-. daloulty in each case arises from
-. fact that the subway which win
~. under the public building and the
w.rket street subway, must dip to a level
nslderably lower than the normal depth
Of the tube.
A. the track level of the subway will
4. from 10 to 12 feet below the city
.,.,er level. large quantities of water
All seep through the rock and the con-
,re,e foundations of the subway and
..urally will flow into the pocket
seated by the dip in the tube. All
heavy gases and foul air also will sink
,,,o this pocket by virtue of their nat
,val weight The problem for the engi-
,eers will be to prevent the accommodating
water and the gases from interfering
with the operation of the trains.
The drainage problem may be realized
hetter when It is understood that the
~ approximately 25 feet below the sewers
running under Market and Broad streets.
After considerable study the engineers
manning the subway decided to follow
Inc example set in the construction of
The New York subways and locate
"sumps' at regular intervals.
sump in engineering means a pit be-
low the working level of the excavation,
into which the water will drain In the
A..g1
Ing the drainage water collecting there
will sink into the ground gradually, but
sump in a subway is usually so near
the bed rock that the water cannot drain
away naturally. Pumps must be used
accordingly to empty the sumps.
In the section of the subway running
beneath City Hall half dozen such
pumps will be located, all connected by a
is-inch drain pipe. The sumps themselves
will be two by three feet in size. The
drainage water will flow into these sumps
from the bottom of the subway then will
be pumped 25 feet into the street sewers
BY means of two submerged vertical shaft
centrifugal pumps, each of 600 gallons per
minute capacity. The pumps will be op-
Grated by electric motors automatically
controlled.
In building the Market street subway
several small drainage sumps of similar
UdtuIt WtIb COHSlTuCleu. AS lIle
level of the Market street line is only
few feet below the top of the main
sewers, the engineering difficulties there
were not great. Small pumps to empty
the drainage sumps under Market street
are now in operation along the line of
the present subway at 22d, 18th, Juniper
and 9Th streets.
The ventilation of the Broad street sub
way will be less difficult, although none
the less important problem than the
drainage. The present ventilation system
Of City Hall. with it's series of air ducts
and air chambers, will be used as a basis
for the subway ventilation. The complete
details Of the system have not been
worked out as yet by the engineers in
he City Transit Department. but II is
believed that large fans will be installed
to drive the gases and bad air from the
pocket Of the subway into the air ducts
and stacks now in use in the City Hall.
Al the same time the pumps will draw
IN constant current of fresh air.
The specifications under which the con-
\ factor will work require that the pres
ent ventilation system of City Hall must
not be disturbed during the process of the
obstruction of the subway. Where there
Is likelihood of dust and unpleasant
doors, a partition must be constructed
which will make an air duct Of the upper
part of the basement corridors and of
Basement rooms which contain heat
ducts