New-York tribune. [volume] (New York [N.Y.]) 1866-1924, 1896-04-28


be at least eight dlamond-drill holes on each
side of the river one in each corner OF the two
tower caissons. The Commission at that time d.
rected them to be sunk at least ten feet into solid
rock. wherever it might be found. The hrst Dor
ing. continued Mr.. Buck. was begun at the north
easterly of the NewYork tower site
early in April. Delay and trouble were expe-
rlenced with this hole due partly to the instaa-
ton Of the drilling plant and partly to the pecul-
lar obstacles encountered. The engineers expect
much less delay with the remainder Of the bor-
ings. Continuing Mr.. Buck said:
THE preliminary borings had indicated rock at
fifty feet below high water. about fifty feet from
the place where the present hole was made In
making the diamond-drill boring the contractors
first sunk four-irch iron pipe through the over
lying mud and sand until it rested on rock. In
stead Of this two-inch pipe was then put down
for the diamond drill to work In. 1t is necessary
that the pipe in which the drill works should rest
closely on the rock in order TO prevent the en-
trance Of sand and to enable the jet Of water
forced through the dr-rod to flush the drlllings
up through the pipe and out at It's top. The drill
then inserted and the borngs begun. The
drlll-rod is about one and one-haK Inches In
diameter outside. and hollow, with stream or
water passing through under pressure all the
time At its lower end Is the dr-bt, small
ring of steel about one-quarter inch thick. into
the lower edge Of which are set. about one-half
al inch apart, eight or ten black diamonds about
one-eIghtn inch in diameter. The diamonds pro-
ject slightly both inside and outside the ring and
form the real cutting edge Of the tool. The drill
rod Is turned by the drilling machine, placed
over the top of the pipe. at speed of about
five hundred revolutions per minute, and is fed
down at the rate OF about one inch In from 100 10
700 revolutions, according to the hardness Of the
rock. A ring is thus cut into the rock and core
of rock Is formed inside the lower portion or core
barrel OF the drill. This core breaks off and Is
brought up when the drill IS removed from the
hole. affording sample OF the rock penetrated
HARD LAYERS OF GNEIss.
1.-The rock found was the typical gneiss. found
all over the northerly part Of New-York City 1t
consists Of hard layers, much like granite. liber-
ally interspersed with mica which gives it
marked but irregular stratifed appearance; the
core breaks off readily at the layers of mica and
the specimens brought up from this hole vary In
length from one to five inches and about one
inch in diameter The irregular,y of the rock
prevented rapid boring. In less than one day.
however. the drill had passed through five feet OF
rock and passed into cavity which quickly filled
with sand, and the drill was stopped. Sound ings
made with rod showed this cavity TO be about
two feet deep and that rock existed below IL. The
diamond drill could not be used again until the
two-inch pipe could be sunk to the lower stratum
Of the rock. four-inch hole was churncd
through the hve-foot upper layer and the two
inch pipe driven down. The drill waa again
started and ran into second cavity after passing
through two feet OF rock The bottom OF this
cavity could not be determined with certainty,
and it became necessary to begin anew at the top
IAN eight-inch pipe was driven 10 the first
rock outside the four-inch pipe. Through this
rock an eight-inch hose was churned and a six
inch pipe was driven to the second stratum.
through which six-inch hole was churned to the
second cavity. and into the solid rock below IL
far enough to give seat for the four-inch pipe
The latter was then inserted and a four-inch hole
was churned about two feet. partly to make sure
that this was not thin layer of material.
The drill was again started and In less than
twelve hours, ending at O'Clock Friday evening.
reached q depth Of seventy and third feet below
high water having penetrated more than fourteen
feet into the bedrock.
at is believed that some two more feet OF
soft rock overlies the bedrock 1t Is probable
that the depth penetrated into the bedrock Is up
ward OF sixteen feet
PECULIAR FORMATION ON THE NETWORK
SIDE.
1.-THE formation of the river bottom at the
end Of Pier No. 49, at Delancey-st.. New-Yorh
is certainly peculiar. and 1t is not possible to
determine until other borngs have been made
how large the layers everything the bedrock
may be. They Of precisely the same ma
terial as the bedrock. and may be pieces de-
tached from, its main body at some other place
/
may be portions Of lodges situated above or be-
low the boring and projecting over IT. 1t is
known that the bedrock does not occur so high
as this until the solid ground is reached at East
st. and that II slopes gradually downward
toward Brooklyn to depth Of about hundred
feet below high water at Broadway and Bed
ford-ave
There can be no doubt that the last rock
found Is bedrock. 1t increased in frmness and
grew harder the depth increased. The en-
gineers OF the new bridge believe that The New
York foundation will not extend more than
sixty feet below high water. which is thirty
feet higher than the NewYork foundations and
| fifteen feet lower than the Brooklyn founda-
tons OF the old Bridge. All OF the bridge plans
have been prepared on the supposlt!on that it
might be necessary to 60 TO this depth on the
New-York side. and on many accounts II Is not
desirable to stop much above this level
THE contractors for the borings are now
fitting up a floating plank. TO be operated In
addition to the one they are now using on Pier
! No. IS. II is expected that two more holes Will
be started simultaneously on the New-York side
before the end Of April. The experience gained
in the first hole will be Of value in driving the
balance of them. An S-inch pipe will be sunk
at the start In each case, and the machines
will be specially adapted to the material already
encountered. The contract calls for the compile
tion OF all borings on both sides Of the river by
June L. and 1t seems probable that they VIII
be finished before that time"