The sun., 1919-06-29
Many Technical Authorities Advise
Further Study Before Going Ahead :
Along Lines That Have Been J.
Approved by Goethals +


amount Of fieXibility has resulted, and
this has eased OF given to the distort-
ing forces that are set up both by the
external pressures and the twisting
movement of the shield itself. as 1t
forced It's way against a wall Of mate
rial which was not uniform in It's
frontal resistance. Mr.. Torgie fears
that the less elastic reinforced con-
crete blocks, interlocked as they will
be, viii not yield in tho same fashion,
but be far more apt to fracture. The
frontal resistance Is proportional to
the diameter OF the face OF the
shield, and in the case of the forty
two foot tunnel this would be nearly
four times that compared with the
| shield used in boring the Pennsyl-
vania Railroad tunnel under the
Hudson.
Gen. Goethals chose the forty-two
foot tunnel in lieu of the planting of
one or more smaller tunnels by the
! open trench method, where the tun-
mel sections would be sunk in an
excavation dredged from shore to
shore in the river bed. Let us quote
what he had to say by way of OBJ
lection to the rival scheme. because II
reveals some details which are re-
lied upon to warrant doing Just what
he opposed. "To build the tunnel It
Is proposed to eXcavate a trench the
bottom OF which is to be eighty feet
below mean low water and to have q
width OF forty feet; to drive piles in
this trench, five foot centres across i,
and eight foot centres longitudlnally
these piles to be from 40 to 70 feet
long after they have been cut off al
the proper elevation, SO that the tun.
mel will shave under It a rock or q
pile foundation. thus assuring the
greatest stability.
THE material through which the
trench must be dug is soft silt ant
mud. Some idea OF the fiuidity OF the
material may be had from tests made
by dropping pole As feet long
weighing 30 pounds. of which IS
feet was Of wood ~ inches In diane
ter. 10 feet OF Is inch diameter steel
under It's own weight II penetrated
the material to q depth of from 81 e
SO feet. The upper stratum, in Close
proximity to the water, is in such 6
liquid state as to be set In motion by
the passage Of deep draft vessels. il
Is true that the material becomes
more compact at the greater depths
yet II Is equally true that water ad
mltted to tho lower strata reduces
these TO the same consistency as the
upper stratum, which will be the cast
il they are reached during the prog
ress OF tho dredging operations. Tt
currents through material which re-
duces to q practically fluid state wheI
water has access to It becomes q seri
Gus and difficult task. an
forced TO the conclusion that tn.
trench method Is impracticable fol
constructing the tunnel on the site Sc
leCted."
Trench Method Not Novelty.
The trench method OF tunnel plant.
ing is not novelty. 1t has been sue
Cossfully employed here in New YOrl
city In linking up a section of ON
subway system which runs under tho
Harlem River. And despite Gen. Goe
thals's stand two civil engineers OF tn,
ACCOMPLISHMENTS Ice Stuart anI
+. Kennard Thomson--have worked
out plans designed to use the trench
method and they are counting upoI
the semi-fiuid nature of the river bee
to help them to clear the way easily
J and to sink and TO secure their TUNE
sections into place once they have beer
properly aligned from tho surface. DR.
Thomson says; THE first requisit,
for a tunnel should be safety; the sec
ond, permanence, and the third
, economy.
"a shield driven tunnel under IN,
Hudson River does not, and will not
comply with any one of these require
ments, as compared with what cal
{ be done by the trench method. TIL,
5 reason for this Is that tho Hudson
River silt Is about 200 feet deep. ant
l any tunnel in II must perforce be
r floating tunnel. For If its weight 4
= made Just right without any live loa'
It will be too heavy with trains or We
2 hicles in 1t. In short It is a physica
, impossibility 10 design tunnel whtcl
l would always be in equilibrium. A
] n matter OF fact the Pennsylvani
, tunnel. probably the best lined tunne
5 In the world. moves up and dow
z with the varying loads of the hig
q and the low tides.
4 "Now "a tunnel that rises and fall
with the tides. as any tunnel mus
c which is shield driven through mate
G rial of this character. would be likel