The daily dispatch. [volume] (Richmond [Va.]) 1850-1884, 1857-01-28

not requiring lining of masonry to S444 and $7l0
per yard, in very loose ground requiring very
The average Of these statements gives sl38 per
f.
The cost of the Blue Ridge Tunnel has been
sos per l. #.
The Black Rock Tunnel in Pennsylvania
through hard rock, constructed by an eminent En-.
gineer, was executed 10 1885, when labor was
nearly half the present rate. 1t is 1882 feet in
length, and cost $l49 l29 its dimensions some.
what less, to cross section, than the Blue Ridge
Tunnel and none of it is lined. $l40, l20 for 1882
feet, would give for 1924, the length OF the Blue
Ridge Tunnel, $3.50 ,656. Add to this &24 600 for
masonry, and we have $354, ,659, being $lO9, 600
less than the actual cost of the Blue Ridge Tun.
mel, difference easily accounted for by the diff
ference in cost of labor the absence OF the facili
ties of shallow shafts, and the expenses Of vent-
lation and pumping, which increase in proportion
to the length Of driftway.
1t may be well to close the description of this
Tunnel, by giving a summary of the leading fea
lures of the preceding statement:
% Dmsn.on. Of Section, 81 high and Is 1sa wide '
Dimensions archsd, 700 f..
CuSis Dis son,snt. so uer iipe.r CUBIC Safr; M
Cubic yds. masonry laid, 1850 cubic yards.
Inclination of grade, 10 IT. per mile
Total cost, &464 0GO
Cost per L. IT,, l08
Total cost per c. I'd, $50
Cost per OK alone, $50
Time of construction, 7years.
N ext to the Great Tunnel in point of magnitude
and far exceeding it in the difficulty of its con.
struction, ia the Brooksvilie Tunnel, which passes
through a projecting spur of the main mountain,
about three miles east of the Great Tunnel Its
length is only 66a feet, and the height of the spur
abe We 1t $50 feet No unusual difficulty was fore.
seen in its construction; iu fact an easy task was
anticipated both by the Engineer and the contrac
tor;-yet of SO treacherous a nature is the rock
encountered, that it proved as difficult an under.
taking of the SORT as has ever been achieved in
this country. No one who has not seen this work
in the various stages of its progress, can well ap.
preciate the untiring industry and perseverance
which has been displayed here. The greatest
credit is due to the contractor Mr.. JOHN KELLY,
for his faithful execution of the work, and his
courage so often displayed at trying times.
The Eastern approach of this Tunnel is an ex
cavation SO feet in DEPTH In rock of nearly hard
a nature as that found in the main mountain, and
through this material $50 feet of the Tunnel is
perforated. But here an abrupt change occurs
and the perfor alton passes into rotten sate ly>
ing at an angle of about 45a, transversely to the
Tunnel and scanned in all directions. The slight-
est disturbance from q blow or blast would
sometimes bring down avalanches of rock into the
Tunnel, leaving immense cavities above to be
filed with packing or propped with timber This
character OF rock continues throughout the re-
mainder of this Tunnel The work of perfora-
ton was commenced on the Western side, and
although much less solid than was anticipated
before opening, still there thought to be suf-
ticent cohesion in the material for the first few
feet driven. Small cracks, however, soon began
to appear, and the roof was partially secured by
vertical props of rough timber. Its appearance
cJntinued to grow still more alarming, notwiih,
standing this precaution and at length a large
crack became Visible in the face of the excava.
tion outside of the Tunnel and about twenty feet
above the entIauce-stil no sliding or falling had
taken place. Twas now determined to introduce
more systematic mode of support and po.
lygonal frames of rough timber, l2 inches in di.
ameter or more, were placed at intervals of 8
feet. 1t was thought that with this assistance
the roof would stand until the introduction of a
brick arch This arch would have been imme-
dately introduced If brick for the purpose had
been at hand, but the necessity for them not hav.
Jog been anticipated, none could be obtained i'm.
mediately.
1t was perhaps fortunate that this was the case;
for the rock not yet having exhibited its worst
features an arch too slight for the purpose might
have been introduced and caamitous consequences
have ensued.
As the perforation proceeded the difficulties
increased, large slides and falls took place, the
rought tmbers were replaced by large, squared
ones, carefully joiated and braced, the frames
were placed only four feet apart, and the spaces
betw cen them supported by longitudinal timbers,
altogether formirg probably the strongest timber
lining ever used for such purposes. The head
ing was driven in this way for i've hundred feet,
and it was then determined to excavate the bot
tom course a. soon as Drlck cOulQ De procured f0r
the purpose of lining
The very heavy timbering used did not prove
sufficient for the weight upon it, and cOnsidera-
BILE length about midway the tunnel and, and un.
der the highest point of the spur fell In, crushing
the heavy bulks inlo fragments, and closing the
almost hopeless ALI we're discouraged, and 1t was
with great difficulty that men could he induced to
work in place so threatening
At length, however, all materials being prepar-
ed the work was resumed. additional timbers
were inserted when required, the bottom course
was attacked and fast ss it was removed, the arch
in was introduced In the meantime that portion
of the roof which had fallen In as before stated.
continued to give way, and at length the whole
impending mass fell 10 to the top in two places.
forming as it were two craters some 50 feet
square at the surface, and some $50 feet in depth.
IL was found necessary to remove nearly the
whole Of the contents OF these cavities through the
tunnel iuto which they gradually descended as
through q funnel, dur ns the removal. When
this was done q massive timber roof was copsiruc.
ted a. q protection to the workmen from farther
ldes, and the arch inserted ~ soon as possible -
Since this much more has fallen upon the arcn,
which, however, is sufficiently strong to bear any
weight thus brought upon il, and he trains are now
passing through the tunnel in security.
The construction of this tunnel under such cir
cumstauces has OF course been very costly
Through material hard ~ that Of the great tun>
mel 1t would have been much less 20, proving that
Inc neIoeSt mktetlal u not Oy euy AaSeos ~ 6toes
an obstacle 10 the work of tunneling ~ that of .
treacherous or doubtful character, however easy
of excavation.
The cost of this work, including all charges,
amounted TO $Il4 600 which 10 at the rate OF $l32
per foot. Two lives were lost during the execu-
tion of this work, in consequence Of the fall Of q
large fragment Of work near the entrance.
The Greenwood Tunnel through . spur of the
mountain about miles below the Great Tunns
on the Eastern SIDE 10 53s feet long. 1t presented
difficulties nearly equsl 70 those overcome 1t ths
Brooklyn tunnel, but having been undertaken
after that work had begun, precautions were taken
wnich experience had shown that necessity for. il
was successfully accomplished without the loss o
. single life, and has been In use for some time =
Il Ia lined with very thick brick arch through
out its length, and . massive portal Of the sam,
material was constructed At each end. The tota
cost was $40 40e, which II u the rate Of el42 PEI
/ foot. No less Than o 600 cubic feet Of timber
and l,924 600 brick wsTs used In is execution.
The inscription stone upon the Eastern portal o
this Tunnel, bears tbs following names:
q. Crozet, On q Et 81 yesr.
Eamd Y, y. Myers, Aest Engineer,