The sun. [volume] (New York [N.Y.]) 1833-1916, 1902-12-21

vices for tunnel driving on the same theory.
Mr. Sooysmith's schem, diffe from tn
Of Mr.. Jacobs's in the beginning because he
holds continuous line OF piles to be
better rest for the tunnel than the isolated
p ers. The tunnel structure, unless material
70 added to give II weight, would be generally
lighter than the silt 1t displaces and would
therefore have tendency to rise rather
than TO settle. This would make any pro-
vision for supporting structure unneces-
gary. were it not that the factor of the
va wing load and weight and the vibration
Of trafhc is Of real Importance. The bed
Of silt which might support. quiescent
load indefinitely without settlement might
load which brought with it a slight pound
ing. The vibration of the moving trains
must be transmitted to a larger mass of
the underlying silt so that the shock will
be dissipatei
Mr.. Sooysmith's plan accepts as true
that a continuous. pile foundation is the
ideal one. and he has called the attention
Of the commission to the pile piers along
the river front which show how great and
permanent the bearing capacity Of such
formation may be made.
To sink this line Of piles across the river
will be comparatively simple. Mr.. Sooy-
smith thinks steel tube large enough
70 receive the pile would be jetted down
in the same manner as pile until its lower
end reached the level at which the bottom
Of the tunnel would be. probably, thirty five
feet under the mud. The pile would then
he telescoped through the tube and driven
through the slit with Nasmyth hammer,
which, with the help of compressed air.
NAV be operated under water.
The piles could easily he driven so that
they would be at the exact level desired.
With this pile support laid Mr., Sooysmith
would then proceed to construct the tunnel
by the freezing process.
In Europe this method has been employed
In sinking many deep shafts. In this coun-
try il has been used but once, for few Jobs
have called for so much work as TO warrant
the installation Of a refrigerating plant
The system has not been used for hori-
zontal tunnel work, but a number Of engi-
neers have given the opinion that it could
be operated perfectly for Just such job
as the Hudson River tunnels will be.
The difficulty and great cost OF con-
structing subaQueous tunnels by COM
pressed air is due to the difference Of hydro
static head at the top and bottom Of the
heading and to the size OF the shield that is
necessary. A small tunnel. not more than
six or seven feet In diameter, may be con-
structed through the most difficult material
with comparatively small expense. But
the Pennsylvania tunnel tubes are to have
an interior diameter OF nineteen feet. which
will make the excavated tunnel about
twenty three feet In diameter. The driving
OF 30 large a tunnel through silt must he
slow and highly expensive. The workmen
have to cope with the difficulties OF working
in a compressed air chamber, and accidents
costing life and meaning delay and damage
to the work done are not infreIuent.
The freezing system as 1t Ia put 10 use in
shaft sinking consists Of sinking vertical
pipes around the site Of the shaft. These
pipes are closed at the bottom and each
contains a smaller pipe open at the bottom.
Brine. cooled by an ice machine, is circu-
lated through these pipes until frozen
wall In made, shutting OF the water and
sand and permitting the excavation and
shaft work to be done within the protec-
ton Of this frozen coNerdam.
For the tunnel work Mr.. Sooysmith has
planned q small tunnel, to be built in the
usual way This he calls the pilot tunnel
II will be about six feet in diameter In the
centre line Of the ina tunnel. This pilot
tunnel will be used as a refrigeration
chamber By maintaining a temperature
below zero, Fahrenheit. in this chamber
the surrounding silt will be frozen into a
substance which may be dealt with much
like sandstone.
The pilot tunnel will be lined temporarily
with metal plates and the refrigerated
brine circulated through pipes laid
against this lining, leaving tho centre un-
INSTRUCTED. 70 that the freezing may follow