The Massachusetts spy, and Worcester County advertiser. [volume] ([Worcester, Mass.]) 1825-1831, 1825-09-07

f.s VIZ 49,
by the surrounding ground in lis natura
tate Of density and solidlty.
10 or"er SO to effect aD excavation o.
hirty-fve feet in breadth by twenty.
five feet in height, Mr.. Brunei propose.
to have the body of the tunnel preced.
I'd by strong framing of corresponding
dimensions. The object of this framing
is TO support the ground, col only in
front of the tunnel, but to protect at the
same time the works of excavation on
all sides. The body of the tunnel, which
is TO be constructed of brick, is intend
ed TO be fitted close 70 The ground; and
IN proportion as the framing is moved
forward, so the brick work is made to
keep pace with it. But as this framing
could not be forced forward all 10 one
body, on account OF the friction Of its
external sides against the surrounding
earth;it is composed Of twelve perpen.
dicular frames, which admit of being
moved singly and independently Of each
other. in proportion as the ground is
worked away 10 front. These several
frames are provided with such mechsn-
ism as may be necessary TO move them
forward, as well as 10 secure them a.
gainst the brickwork when they are
stationary. II is to be observed, that
six alternate frames are stationary,
while the six intermediate ones are left
free, for the purpose of being moved
forward when required these, in their
turn, are made stationary for relieving
the six alternate ones, and so on. Thus
the progressive movement of the frame
can readily be effected.
10 order that sufficien, number of
hands may be employed together With
effect and security, each frame is diyid-
ed INTO three small distinct apartments,
which may properly be denominated
cells. BIZ this disposition the twelve
frames form thirty-six cells, in which
the men are 10 operate for excavating
the ground. Ii is to be observed, that
the ground in front of each cell is 10 be
kept from falling in by means Of pow
ertnl shield, consisting of small boards,
strongly secured by the frames. Ii is
from within the cells that each work
man is TO cut out the ground, jrst in The
way he would do if be were to cut out
recess 10 a wall for the purpose of fl
tipg closet into it but With this pre-
caution, that he is to remove each
board, one after The other, and replace
each in succession as he cuts the portion
of the ground corresponding with IT.
When he has thus gained from three to
six inches npar The whole srl.fnnn. ION
operation which it is expected may be
made in all the cells nearly in The same
time, the frames are moved forward,
aud so much of the brick work added to
the body of the tunnel. Thus in en-
trenched and secure cells, thirty-three
men may be made TO carry On an exca-
walton which is six hundred and thirty
feet superficial area, in regular order
and uniform quantities, with as much
facility and safety as if one drift only of
nineteen feet square was TO be opened
Oy one man.
The drift carried on under the Thames,
in 1909, which was about the size Of
one of these cells. proceeded at the
rate of four to ten feet per day. In
the plan now proposed. ii was not in
tended the progress should exceed three
feet per day, because the work should
proceed with mechanical uniformity in
all the points together.
The estimated expense of this under
taking, 100000. is SO much under that
Of bridge, as to have occasioned doubts
whether it has not been moderated,
Bat 10 remove these, ii is sufficient TO
state. that it will be constructed almost
entirely of brick, which is the cheapest
of all building materials, not merely as
a material, but also in the labor.