New-York tribune., 1880-06-20
DIFFICULT ENGINEERING TORK.

BEGINNING TIE SECOND TUNNEL IN TIE NORTH
RIVER EXCAVATIONS.
What is considered the most delicate and
probably most difficult piece Of engineering that the
excavations for the North RIVER Tunnel have made
necessary has lust been succefsfuy accomplished in
the completion OF the twenty feet OF the second or
south tunnel The first tunnel has nlrendy been driven
$50 feet from the working shaft in Jersey CITY, making
900 feet under the river The shell Of tho tunnels com
posed Of two feet Of brick laid inside OF plates OF boiler
iron plates supported, at hrst at the TOP OF
the tunnel forming what is called an overhang ana
the weight Of the mud lie largely resisted by the use Of
compreesed air. In the first tunnel there s plenty Of
room 40 that the upper plates be readily bOted
IN the plates already completed and the work proceeds
simply and easily. Tho opening Of the second tunnel
h pernaps twenty feet the entrance through the
aIrlock Here one tunnel separates into two. which will
be united again nearing the Ncw-York side
Tn beginning the second tunnel there was nothing
ncrmapent TO work upon The tenacious silt III which
a are being made becomes hardened under
the influence Of compressed air aud cracks falling In
masses II entirely unsupported. aud allowing the ar 10
epcape The iron plates are inserted at hrt on the top
and IL was necessary devise some means OF support
Ing them as Of COURSE the arch could not be completed
until the work had been pushed far enough ahead TO
allow sufficient room. Special arrangements were
therefore made for holding these plates in position until
the ring could be completed secondary arch OF iron
mates called bridc," was thrown across from the
north tunnel, the Dr lie DclnG supporter
I'm noSittOn by arch thrown up from rue tOth
stde of the tunnel already constructed Ihs FORMED
fpmnOrary roof which, together wtn the pressure OI
comnressed air. served TO protect the wOrken as t'y
nroceeded with the construction OF the shell Inc nSt
mari of the work WIS exceedingly SLOW ana teGlonH'
Small excavations made at the top under the per
sopal supervision OF the superntendcn ana inc sl wa
nassed out from TO man In buckets ike thc Olu-
fashioued lines mt AS as large enough space
was cleared away iron plate was Inserted ana heu
rbe Sit in the centre OF the tunnel core Of about ~
teen feet I'm diameter lett undsturDed, ana thc
iner after long and careful work. eXcavaod passage
ahnut four rect wide all around this core b0nR the
nlates I'm position they proceeded, ana sc ulg thr
from lateral pressure by or braces llAccd akast
the core AS soon the shell connected. me
masOns proceeded buIld along and inside Gf n bIck
Ta two feet I'm thickness In tins way the hrst nVc ieci
~ ihe tunnel were bnt The space between the brick
nacted nng and the whole was allowed 10 remain fol
seyera davs in order that tho silt along the exterior O
rho iron shell might settle firmly INTO position De1Oc thc
m,nera proceeded with the work fcw days ago IL wac
Judged safe begin eXcavating. Thc core OF Blu WuS
dug out ann the miners, protected ny tne IRON sucI
Ave feet wde began eXcavatng the Sill belOre hcll
and uniting plates advance, as III inc hOrtL
tunnel AT present about twenty feet OF the ROuth tu
mel are In course Of construction but since the com
DetiOn Of the first five feet 1t mas not been ounu neccS
| sary to leave the silt core. ,
The reporf that the wOrkmcn in the tunnel euher from
| uI-heath and have a tendency to malaral levers
tuemselves TO be perfect health aud secuted the idc
Of any sIckness arising from their work. The tennerI
ture Ia the tunnel Is pleasant aud equabe ranging IRON