The New York herald., 1876-09-16

reef produces eddies on.oon sides OF according TO
the direction OF the tidal currents much In the
way OF vessels coming down with the ebb the effort
TO hug tho shore. and thus avoid being thrown the
middle reef II Is the way OF small and large vessels
equally and Its removal is an essential element In the
Improvement of tho channel"
OPERATIONS HALLErr's POINT KKEY
When II was found by experiment that the pecu-
liar conformation OF this great projecting mass OF
submerged rock rendered any attempt removing Il
by surface blasting fruitless it resolved to resort
10 the more elaborate and tedious plan OF drilling
adopted by General Newton for the removal OF the
otner detached rocks In the East River The surface
blasting system was very simple one. but not always
effective Charges powder weighing about 125 pounds
enclosed in tin made perfectly water tight were
laid the surface Of tho rock aud fred by Of
voitac current The weight OF tho superintendent
water was considered ns acting as sufficient compress
sive force tampng and the effect tho rock in the
immediate vicinity OF the explosion snattcr It
that the could be easily detached and
moved by graphing The plan answered very we'll
where sharp projecting rock surrounded by deep
water into which the debris was blown, but where
large surfaces presented themselves such that Of
the Hactts Point Reef, thcre was no chance for the
broken rock to free itself from the main mass. and
consequently the plan of surface blasting failed.
The system OF drilling is extremely tedious and
pensive and tho chief object OF the undertaking
complete It In the shortest possible time consis-
tent with the complete removal Of tho reef the late Mr.
G. c. Reheimers plan OF subaqucous tunnelng for the
removal OF rock obstructions channels at once
adopted by General Newton and indorsed by tho other
government engineers. This ''ihe FIRST time, so
far as known" according to General Newton, THAT
tunncing was suggested means OF removing rocky
distractions in n chanueln and lar as the opera
tons have progressed at Haletts Point tho
engineers have found to regret the adoption
OF this new system.
THE CHARACTER OF THE WORK
The ledge AT Halett's Point as shown by tho accom-
panyng plans, projects into the waterway Of the East
River He'll Gate in a northessterly direction The
triangular shaped surface within tho limo Of thirywo
feet soundings extends outward from It's base, rest
ing the mainland to It's apex at tho thrtytwo foot
line about 400 feet The excavation. however, is not
carried further than the twentysix foot line, al
thought few points the headings have been run
the ull distance From the trapezoidal shaped shaft
the shore ten man headings have been driven
radiating outward Gnd these form the basis OF tho
general plan Of the subtcrranean submarine excava
ton.
During the progress Of driving these main tunnels
supplementary system Of excavation was also carried
and the headings connected by series of nearly
semlcrcular galleries, having the centre Of the shan
sectors between the main headings have been again
divided by ubhcadngs until the entire space within
the area desired to be excavated has been followed
out the roof rock forming the present bed OF the
beng supported Oh natural rock columns which
have been left untouched for that purpose.
AS the ledge shelves away into deep watcr with
varying slope from the highest point represented by
the site the present main shalt, the length, direction
and gradients of the different headings had necessarily
be subordnated to the peculiar contour Of the rocky
mass ana the utmost care had to be observed in
preserving the thickness OF ten feet between the upper
and lower surfaces OF the roof rock which covered
tho excavation. IL must bc remembered that IN cxca
waiting this immense submarine chamber or system Of
quantities of powerful explosives had 10 bo
employed and the repeated shocks caused by the rend
ing and tearing away OF this solid rock were OF
transmitted TO every part OF It's mass In pro-
PORTION their distance from tho centre OF genera
tion. Now, careless use OF any Of these powerful
agents would be likely shatcr the thin shell OF roof
rock and cause drowning out OF tho workings by
an uncheckable leakage.
As IL was when tho work OF driving the headings
was nrst started tho Of tho ledge surface
not complete IN the vicinity OF the operations, conse
qucntly the tunnel excavated at haphazard and
the roof rock between It and the river thinned
awav TO about four feet thick The result great
leakage which compelled the building up OF masonry
shield against tho face OF the excavation near the roof
and the lowering of the direction OF the heading
respond with the dip Of the ledge into deep
water.
BY tho most careful management and untiring watoh
tuness this work is complete so far As the
excavation goes and nothing remains but to load all
tho supporting rock columns, which arc already pre-
pared and drilled for tho purpose as described IN tho
HERALD and then send the electric spark its mission
of destruction.
HEADINGS AND GALLERrBs
To convey proper idea of the OF tho OPERA
tions on the HaIlets Point lege It is necessary to pro-
sent table giving lengths Of tho headings
and sub.headings with tho scmcircuar galleries that
connect them These aggregate over 400 feet and in
cludc all thc cuttings made through tho ledge except
that necessary to sink tho main shaft. The debris OF
this excavation been brought out Of the workings
,p.o the main shalt on cars running narrow
paueo tram roads, the boy OF the loaded car beng
lifted from It's truck by powerful derrick and the
tents deposited tho spoil bank or great heap Of
finely broken up rock which has been taken out OF tho
shaft since the OF the works In October,
,soa The size OF the shaft is III by 80 and ts
depth below the level OF low water,.3 .33 feet. All the
a,er that accum the works by leakage Is led
TO the pumps through the headings, that part
Of the excavation is controlled by the pumping power
and can be dried without difficulty by the Cameron and
the Blake pumpa in use
r.nlE OF LENGTHS HEADINGS AND 0ALLBRTEa
Feet
Heading No. l, main .....-.................. 1868
Heading No q main ACKNOWLEDGEMENTS. 1s5 70
Heading No. g. main. ....-.................. lgyy5
ue,d,ne No 4 NEUTRALITY-SUSPICIOUS.. le453
Heading No s. main Observation-Disclosures. l9l %
Heodine No g. ........................ 22s 0s
Heading No 4 main n......................... $50 So
ueading No s. ain........................ 2l3a2
Heading No o. nam ain........................ 225 SO
o. u. a..