The sun. [volume] (New York [N.Y.]) 1833-1916, 1915-07-11

Will cost a little more than 500, 900.
1T will he readily appreciated that
the u~nderpinning OF buildings along
the route is a very prominent factor
in the work. says Mr.. Madden. THE
the number Of large and heavy build
ings. few Of which have foundations
to rock or hardpan, and with these
exceptions all other foundations are
above the subway subgrade and uni
above water level as well.
There are forty-fve buildings of
less than EVE stories assessed valu-
alton $1,000, 000), twenty buildings of
from seven to twelve stories in
height assessed valuation SIS, 900, OO0).
and ten buildings Of from thirteen to
twenty stories in height tassesed
valuation 5000. 000). Aside from
three of the caisson type the founda-
tons include wooden piles supporting
concrete footings. steel and concrete
grillaxes and continuous concrete
base walls.
irrespective uf the present con-
.struction the work in connection
Will III subway hlubt bc COhuuStVu
with the view of not only perma-
nently transferring the building loads
TO an adequate bearing outside OF
the influence OF the contemplated ex-
cavation, but. in addition. Of secur-
ing all underlying ground from n
displacement which might affect the
integrity Of any portion Of the abut-
Ting of adjacent buildings"
How have the engineers proceeded so
far? Mr.. Madden avs
"The method OF UNDERMINING con-
templates the least possible disturb
ance Of existing foundation piers or
footings and is accomplished by intro
ducing longitudinal steel beams or
Orders judiciously close to the bot
tom OF the foundation. between which
cross beams are placed on each side
at each pier. and this steel grillage
is then pinned into the footings and
concerted solid, producing, in effect.
a supplementary spread foundation.
"Excavation Is then started be-
tween each set Of piers for an under
p,nning pit below the grillage and the
sides OF the pit are protected with
carefully placed horizontal sheeting
boards as II increases in depth. This
continues until ground level is at
tanned. below which steel castings
fourteen inches in diameter are sunk
in two foot lengths with hydraulic
Jacks until they extend a proper dis
lance below the bottom n, the pro-
posed subway excavation.
when the required depth has been
reached the casing is filled with con-
crete, and when the full number or
piles are In place the Pit Is con-
GREETED to within about two feet OF
the concerted grillage and, with verti-
cal street struts, a direct transfer or
the load Is effected by use az steel
wedges and steel bearing plates, and
this remaining space Is then con-
GREETED and grouted solid with a rich
cement grout. Grout IL very huid
cement which permeates and FILE up
all interstices.
"On the completion of the pit the
foregoing operations are repeated until
the requisite number for adequately
supporting the building loads have
been provided. In most instances
these pits are made continuous by
successive operations so as to form
"A cut of wall for the entire length
Of the building, thus preventing any
displacement OF soil under the inte-
rior floors or footings lying behind
IN cases, however. where the ma
terial encountered will permit the
pits are connected with close sheet
ing: that is. tongued and grooved
planks, to attain that purpose. These
cut off walls are extended across each
intersecting street. Up to date the
results have met every expectation
and the progress has exceeded the
original estimate. In fact we have in
this way underpinned all OF the
buildings contiguous to Hanover
Square"
I Perhaps some readers may not he
able to understand perfectly the terms
Mr.. Madden has used BY heading
he means the e~xcavating done imme-
diately under the two layers Of heavy
planking which take the place of the
asphalt paving of the street. Grill
age" Is that building up Of timbers
placed crosswise which answers for
the time being as a support, and this
arrangement of grillage Is n of the
restless processes Of the work. In some
cases great wooden girders a full foot
square in cross section and many
feet long, rather appropriately called
needle beams are laid beneath the
street crosswise. and then, as the
dirt is dug away under them, support
ing posts. equally sturdy but not
more than six feet long, are placed
upright to hold the needle beams
aloft. 1t Is in this fashion That the
excavators get deeper down stage by
stage.
The cutting from time to time has
uncovered gas pipes, water mains
drains and sewers. These the sub
way builders disturb as little as pos.
sible. When finished the William street
subway will have q total length OF
2,643 feet. The structure will be OF
! standard two track type. requiring ar
/ excavation about 20 feet in width
which at stations will he Increased
to the fun width of 40 feet between
the building lines to provide for islant
platforms, from which stairways will
extend to a mezzanine passageway
connecting with the entrance stairs tC
the surface.
The depth to subgrade will vary
from % to 81 feet below the surface
and in general the excavation will ex-
tend from 3 to 5 feet below mean
high water, with a maximum of IL