Clinch Valley news. [volume] (Jeffersonville, Va.) 18??-2019, 1900-03-30

John y. o'RouYke. one Of New Ycrk's
best known and most experienced enc
gineers and contractors. said: This
tunnelipg through the rock in the
several sections specified. The men
employed In that work find no conflict
ing Interests to obstruct their speedy
progress. It Is practically all blasting.
In cutting the tunnels for the new
subway, the engineers in charge will
start the work in two ways. One Is
from portals cut into hillsides at the
desired levels. and the other is from
shafts sunk from the surface OF the
higher grades. In both cases the
method OF blasting will be the same
Having determined the dimensions OF
the hole to be cut, which in this case
VIII be thirty feet wide and twenty
feet high, a gallery or heading at the
top is prepared by the blasters from
which to operate with drills on the
greater mass. The headings will be
about seven feet high and eight to ten
feet Wide. and Will be carried ahead
about 100 feet of where the excavation
is being made the full size OF the tun-
mel
To start heading a V-shaped cut
is first made by drilling six holes with
two sets Of drills about three feet
apart, and placed at such angles that
the holes cut meet at a triangle point.
They are charged with high explosives
and discharged simultaneously, fore
Ing out the shattered rock and leaving
the V-shaped cut. three TO four feet
deep, in the rock. Then two rows OF
holes, four each, are drilled straight
into the rock at either side of the
heading. These are charged and ex-
ploded, the blast squaring of the en-
tire cut to the depth OF the V-shaped
cut first made. The whole operation
is repeated until that particular Sec
ton or tunnel is completed.
Bench and Heading.
once the heading has reached the
proper length, another gang, larger in
numbers than the first, occupies the
cleared floor space Of the heading.
They drill downward at all angles tn
the limits OF the prescribed measure
ments. In the meantime the workers
at the heading are cutting It further
into the mass, so that the work on the
bench, as the full clearing is called
Technically, and the work on the head
Ing proceeds continuously and stimuli
taneously. Thus the progress is rapid.
an advance of 125 lineal feet a month
being the average. The shattered
fragments are removed by cars
promptly after each blast to the por-
tai or shaft, as the case may be. and
carted away for other uses. 1t is a sim
gular thing that in blasting the in
ner end of the charge never skaters
the rock to the full depth. 1t is like
powder In a gun in that respect For
that reason the cuts are always about
Two feet short Of the length of charged
holes. Blasters have given this I'M
exploded bit the technical name gun
because of the similarity.
The Greatest Dimcu:ty.
THE greatest difficulties to be over
come in carrying out the contract will
be found in the open or cut and cover
work in places where surface traffic is
congested and where large buildings
are close by. IL the ground happens to
be bad. In such cases provision will
have to be made for the accommoda-
ton OF the traffic and the protection Of
the buildings. This will be true par
ticularly in Park row, Forty-second
street, Broadway and several other
points. There are two ways by which
these troubles may be alleviated. One
is to work only one-half the width of
any such thoroughfare at time, leav-
ing the other half for the use of traf-
&c. In upper Broadway the contrac-
tors may brace the trolley structure
up on supports while cutting out their
ffty-foot subway beneath, or they
may move the tracks and all their be-