410 
between the shores of a great river, 
without occasioning any obstruction to 
the navigation, has long been a desi- 
deratum of considerable importance 
with the public, and in the estimation 
of scientific engineers.. The difficulties 
which have opposed themselves to 
every attempt that has been hitherto 
made to execute a tunnel under the 
bed of a river, have been so many and 
so formidable, as to have prevented its 
successful termination in those in- 
stanees where the attempts have been 
made. - 
To propose, therefore, the formation 
of a tunnel after the abandonment of 
these several attempts, may appear 
somewhat presumptuous: on inquiring, 
however, into the causes of failure, it 
will be found that the chief difficulty to 
be overcome, lies in the inefliciency of 
the means hitherto employed for form- 
ing the excavation upon a large scale. 
' In the case of the drift-way made 
ander the Thames at Rotherhithe in 
1809, the water presented no obstacle 
for 930 feet ; and, when a great body of 
quicksand gave way and filled the 
drift, the niiners soon overcame this 
obstruction, and were able to procced 
until they were stopped by a second 
irruption, which in a few minutes filled 
it. Nothing comés moré satisfactorily 
in support of the system that is 
adopted here, than the result of the 
operations that were carried, under 
that circumstance, to an extent of 
1011 feet, and within 130 feet from the 
opposite shore. 
It is to be remarked, that at the se- 
cond irraption, on examining the bed 
of the river, a hole was discovered 
four feet diameter, nine feet deep, 
wiih the sides perpendicular ;—a proof 
that the body of quicksand was not 
extensive ; but what is most remarka- 
ble is, that this hole could be stopped 
merely by throwing from above, clay 
parilyin bags and other materials : and 
after pumping the water out under a 
head. of, twenty-five feet of loose 
ground, and thirty feet. of water, the 
‘Miners resumed the work, and pro- 
ceéded a little further ; but finding the 
hole at the first irruption increased, 
and the filling over the second very 
much sunk, the undertaking was aban- 
‘doned. 
The character of the plan before.us 
consists in the mode of effecting the 
excavation, by removing no more 
earth than is to be replaced by the body 
of the tunnel, retaining thereby the 
A New Plan of Tunnelling. 
[Dec. 1, 
surrounding ground in its natural 
‘state of density and solidity. 
In order so to effect an excayation 
thirty-four feet in breadth by eighteen 
feet six inches in height, the author of 
this plan proposes to have the body of 
the tunnel preceded by a strong fram- 
ing of corresponding dimensions. The 
object of this framing is to support the 
ground, not only in front of the tunnel, 
but at the same time to protect the 
work of excavation in all directions. 
The body of the tunnel, which is to be 
constructed in brick, is intended to be- 
fitted close to the ground; and, in pro- 
portion as the framing is moved for- 
ward, so the brick-work is made to 
keep pace with it. But as this framing 
could not be forced forward all in one 
body, on account of the friction of its 
external sides against the surrounding 
earth, itis composed of cleven perpen- 
dicular frames, which admit of being 
moved singly and independently of 
each other, in proportion as the ground 
is worked away infront. These seve- 
ral frames are provided with such 
mechanism as may be necessary to 
move them forward, as well as to 
secure them against the brick-york 
when they are stationary. It is to be 
observed, that six alternate frames 
are stationary, while the five interme- 
diate ones are left free for the purpose 
of being moved forward, when re- 
quired ; these, in their turn, are made 
stationary for relieying the six alter- 
nate ones, and so on. Thus the pro- 
gressive movement of the framing can 
be effected. 
In order that a sufficient number of 
hands may be employed together, and 
with perfect security, each perpendi- 
cular frame is divided into three small 
chambers, which may properly be 
denominated cells. By this disposition, 
thirty-three men may be brought to 
operate together with mechanical uni- 
formity, and guite independent of 
each other. ‘These cells, which 
are open at the back, present in front 
against the ground a complete shield 
composed. of small boards, which 
admit of being removed and replaced 
singly at pleasure. 
It is in these cells that the work of 
excavation is carried on. There each 
individual is to operate on the surface 
opposed to him, as a workman would 
cut out a recess in a wall for the pur- 
pose of letting in a piece of framing, 
with this difference only, that, instead 
of working upon the whole meee Be 
takes 
