Memphis daily appeal. [volume] (Memphis, Tenn.) 1847-1886, 1882-05-21

hat the greatest difficulties of construction /
have been overcome, that they assert that |
The successful completion OF the work Is now |
but a question of time. The entrance to the |
tunnel on this side Is at the foot OF Morton !
street, between piers Nos. Al and A North |
river, and at this point has recently been
completed what Is considered a triumph OF
skill.
FROM THE JERSEY SHORE
two tunnels have been extended under the
river bed, the southernmost for distance OF
500 feet, and the northern 1000 feet. In the
latter, so CON paratively easy Is the work, the
workmen are constructing about three feet Of
tunnel day. No work Is IN progress in the
former, as it has been found that it is more
economical and in every way better to work
in one tunnel only at one time. The system
pursued in the excavation and building of
the tunnel itself has already been described
at length in the columns OF the Times. While
the general theory OF construction on this
side of the river is the same SIS that pursued
on the Jersey side, the formation of the earth
has necessitated very different method in
the details. Difficulties met with on this
side were not encountered in the sinking OF
the Jersey shaft.and the opening of the tun-
nels there Here the soil is coarse sand,
readily allowingthe passage OF water through
it,; there the soil is clayey, and the silt
under the river bed is impervious to water.
The work on this side, if wholly successful,
as it now promises to be, will be Won
der OF engineering art. 1t Is the first time
that a work of this character has been at
tempted where compressed air has been used
as 4 partial safeguard in the penetration OF
a soil which not only absorbs, but allows the
passage Of water through it. General Sooy
Smith, the former engineer, opposed the use
of this method, and advocated the substitu-
ton OF another, and, as he thought, less
dangerous plan, but he was overruled. The
peculiar form alton of the soil on this side
necessitated the sinking of a caisson, instead
OF the use of shaft, as was done on the New
Jersey side.
THE CAIssoN
is forty-eight feet long, twenty-nine and
half feet wide, and twenty-six feet in hight,
outside measurements, and Is sunk so that
its bottom is ffty-six feet below the mean
low-water mark and sixty-five feet below the
surface of the street. 1t is made entirely OF
wood, its walls are three feet thick, the sides
having a slope of one-half inch 10 the foot,
SO that Its interior somewhat resembles the
slopiDg sides of an inverte. funnel. 1t is
one third larger than that used on the Jersey
side and weighs 400 tons. On top of the
caisson coffer-dam in three compartments
was constructed, these compartments
running east and west across the
nine feet in width. In this are the &ir-locks
admitting TO the base OF the caisson
and thence 10 the tunnel proper. The two
side compartments are filled with the mate
rial removed from the excavations, thus SER
wing as load for the caisson. The whole
arrangement, with its load, weighs about
$500 TONS The caisson is, OF course, air
tight. When the caisson was sunk to its
proper level the bottom of the lower halves
tNrfr
side the caisson. The work thus far was
comparatively easy, but that which has fol-
lowed during the past four weeks, the open
ing of the north tunnel, has been watched
with much interest by engineers. 1t consisted
in cutting out the side of the eaisson west
ward, and the construction Of the iron bulk
head and of the tunnel walls, every step in
which work was desperate fight against the
yielding earth and the permeating water.
When the side of the csisson had been cut
through the work OF excavating the earth
haa to be carried on very slowly and care
fully, for a new and unanticipated difficulty
was met with. In addition TO the pressure
from above and from the sides, there was
found to be an upward pressure OF water
from the bottom Of the tunnel twenty eight
pounds to the square inch. The water that
found its way TO
THE TUNNEL
from below was found to be fresh, and to
come from the southeast, where seemingly
there is an underground spring, whose waters
make toward the river. How long this
newIy-discovered trouble will annoy them is
purely matter OF conjecture with the en-
gineers but they think that they have dis
covered plan of successfully battling with
the possible leakage from above or below.
Where the rough excavation at the heading
is made, circlet of iron plates, set together
against the soil so that they are alright, is
constructed. This plan differs from that
heretofore used in the work only in the sub
stitution of smaller and variously shaped
plates in place OF the four by two and hall
feet plates used on the other side. This
change was made so that the exposed sur
faces could more quickly be covered and the
| leakage, if any should occur be more easily
| stopped, and the treacherous soil be pre-
| vented from caving in. The plan has thu
| far proved eficacious, and the first section o
| the north tunnel, twelve feet out from th'
| caisson, is completed. Workmeu are nov
Dushing forward the construction of the tun
| mel in the heading extending ten feet further
| toward the river When this section is com
pIeted and work further out toward the river
| is begun, a new obstacle is to be met with
and overcome. From the heading to beyond
the river bulkhead wall Is a distance
| of forty seven feet, but before the tunnel car
pass under the wall it must pass through thu
earth into which the piles on which thu
bulkhesd walls rest are driven. But littl
| trouble is anticipated, however, the plat
| being to cut these piles off aud build tn
walls of the tunnel of twice the 9rdInar,
| thickness, in order to support the additiona
| weight imposed. Once beyond this
WALL OF PILES,
and under the river bed, it is thought tina
the progress onward and downward will b
comparatively easy, fer il is expected that a
| a distance of from 800 10 AGO feet from tn
| caissoh the workmen will strike the I'm
| pervious silt, which permits OF much NOR
rapid progress. Fifty ieet below the meal
low.water level the opening cut is situated
| but the tunnel must descend considerable
below this level before the middle of tn
channel is reached, for at that point tn
deptb of the water is sixty-three feet. Wit
he increased depth OF the water comes a
increased pressure, necessity tor heayIe
masonry, and more problems which ma
defy theoretical engineering. The eDgir
GERS in charge are confident, how
ever, that the penetration of th
treacherous soil on the New Yor
the most formidable obstacle to be overcom
Others, however, think that the create
difficulties are yet to come and the create
skill vet to be exercised in successfully ca
rying the tunnel under the bed OF the rive
channel. The engineers in charge are col
fdent that if no greater obstacle than hi
vet been met with is to be overcome, tt
work can be completed within the five yea
time specified for its completion. There al
now
THREE GANGS OF wORKMES
employed at the New York end of the tut
mel, each working eight hours at time ]
; the compressed air, which has pressure
| about twenty-five pounds to the square inc
, above the normal pressure. None Of the
men have as yet suffered from the dlsea
known as ''the bend" which so frequent
anuoys men working in compressed air. In
is due to the fact that the effect Is b
coming better known il is more easily cou
: teracted, and every precautisn to gual
against the suffering of the men, as well
= against accident, is taken. On the Jers'
| side the danger from this disease Is AVERT
by the use of a secondary alr-loek IN Whl.
the pressure is five pounds less than IN q
lock at the heading. After breatalng Tor
few minutes this less dense air, the workm
mass into the air at a normal pressure. As Il
system has been found to afford relief, It W
be used on this side as soon as II Is posslt
tn do 40. The electric light has done avs
TO a great extent, with the annoyance irc
the smoke of lamps or candles, but as The
= latter lights have 10 be used ID Sorki
among the huge braces used IN proppIng
the walls experiments are now being ma
to produce a wick which will not smoke.
extra engine for comprising the air lore
into the heading stands idle in the engiI
. room on this side Of the river, for use IN Ct
e of an emergency, or the giving out OF e1tt
- of the two engines constantly II use lie
= phouic communication is had with the
eine-room from the tunnel. An extra Ia
i provided for use in case the water 81
a ply should be cut of in any way, and IN
= are two air-loeks in the cofier-dam, 50 tina
le repetition of the disaster which occurred
!, the Jersey side would hardly be possible
!" case of a Ieaksge or caving in OF the he
ing. One of the locks used on this sld'
y the one constructed for use on the Ier
= CITY side, and through which the bodies
= the twenty men killed in the accident
70 brought from their place OF burIsl IN
I 81. uLzff