The Sun.
London, England, 1865-02-13 00:00:00

The Thames Embankment•

It will not be for the want of excellent practical ex-
amples of the science if the general public do not
become in a rough and ready sort of way tolerable
engineers. No one can walk far now-a.days, or
journey much by road or rail, without coming in
sight of some stupendous mechanical contrivance for
facilitating traffic or erecting bridges and buildings.
The Thames Tunnel is a mere trifle as an engineer-
ing work to what has been accomplished in the sub-
terranean railway, and the subterranean itself is
about to be outdone by its own extension, for
the completion of which it will be necessary to make
a second tunnel underneath the first. Tunnels,
viaducts, and scaffoldings are, in fact, familiar to
every one. Of the latter we have in London just
now four excellent specimens—that for the bridge
at Cannon-street, that which forms the temporary
bridge at Blackfriars, that for the removal of the
old bridge, and that which will soon dam out some
10 or 11 acres of the Thames, and reclaim it
for the great Embankment between Westminster
and Waterloo. Just now the works connected
with this really gigantic undertaking are in full ope-
ration, and the whole series of processes by which
cofferdams are commenced, continued, and com-
pleted can be watched in all their stages, from the
first pile driven at Hungerford-bridge to the perfect
series of caissons which now shut out the Thames
from the large area enclosed below Westminster.
It will probably be very long before Londoners will
again have such an opportunity of studying practi-
cal engineering on the most extensive scale. Steam
and hand pile-drivers, steam and hand pumps,
steam cranes and travellers, with steam machinery
for driving air-pumps ; men working at the top of
lofty timbers, or down in the darkness far below
the bed of the river, filling the cofferdams by sluices
to flush out the mud, and then pumping it out again
by steam ; with stones, bricks, rubbish, offal, dirty
water, and all the unsavoury flotsam and jetsam
which go to make up the river Thames—these and
a hundred other operations and contrivances are
always in work day after day, and from morning to
night.

The works next to Westminster-bridge are those
which attract the greatest amount of public atten-
tion, for there everything can be watched from the
pumping out of water to the puddling in of clay be-
tween the timbers of the cofferdam, and here also
can be seen the whole plan of struts and cross
timbers which enables the iron caissons to keep out
the whole flood of the Thames for a depth of 40ft.
above them, and resist a pressure of no less than
120 tons on each caisson. From no point of the
river can the whole system on which the Embank-
ment is to be built be better seen than here, for
here are both the iron and timber embankments
behind which the massive granite face of the real
Embankment is to rise. The method of building this
iron cofferdam, though very simple, is from its very
simplicity of great interest. The caissons are elipti-
cal tubes of wrought iron rings or belts, each ring or
belt being 12ft. long by 7ft. wide and 4ft. deep, with
a flange or edge that admits of the rings being bolted
one to another. Three or four of these rings are
bolted together and sunk between guiding piles to
their proper position in the bed of the river, then
others are similarly added on till the height of
.the
whole is sufficient to raise them above high-water
mark, and the weight of the whole is sufficient to
sink the hollow tube of iron which they form through
the soft mud on which they rest and keep them
water-tight from below. When this result has been
attained the water is pumped out and the tube gra-
dually weighted with iron to force it lower till it has
reached a fair depth, and has a firm hold in the
ground, when the agency of the pneumatic machi-
nery is called.into play. After the workmen have
descended and dug out the gravel and shingle to a
depth of some 2ft. or 3ft. below . the lowest in-
ternal edges of the tube, a weight of 60 tons of iron
is placed upon it from the inside, with an air-tight
iron cover, which closes in the top. Through an
aperture in the top of this cover the air is forced in
by steam power till it has reached a pressure of 81b.
to the inch—a pressure which dilates the tube more
than half an inch in all directions, when the air is
suddenly released, and the cylinder as suddenly
contracts and sinks through the earth which it has
itself enlarged to a depth of 2ft. or 3ft. lower. This
process has to be repeated over and over again till
all the superincumbent mud and silt and gravel has
been penetrated, and that mysterious geological
compound like heavy, brown plaster of Paris,
though as hard as marble, and known by the name
of the London clay, has been reached, when no effort
of modern engineering can contrive to get any-
thing much further. The presence of this London
clay on the banks of the Thames varies in an almost
unaccountable degree. In some cases it crops up
close under the mud ; in others it can only be
found after a laborious penetration of 40ft. below
it. Thus one caisson may only penetrate 10ft. or
or 12ft. below the surface, and its next neighbour
may have to go to a depth of 40ft. or 45ft. Once,
however, that it is reached the sinking of the cais-
sons stops, they are merely filled up to the level of
low-water mark with solid concrete, and thus filled
they will remain till the time shall come when the
Embankment itself will totter, for behind them it
is intended that its foundations are to be built, and
it is to be hoped to last for centuries to come. The
lower parts of these iron banks are never to be
removed. The upper parts, which now shut out
the Thames at Westminster, will of course be taken
away as the wall of the real embankment is built
behind them.
To take this part as exemplifying the process of
construction, we have here a length of 240 feet of
iron caissons towards the river, shut in by a cross
dam near Montague-house, which reaches back
from the caissons to the shore, so as to enclose a
water-tight space of nearly an acre and a quarter.
This space, though enough to make a fair orna-
mental lake, the screw pumps of Messrs. Wood-
wards and Murray soon cleared of water, and as
the supporting mass of this water inside diminished
and the weight of that shut out increased powerful
timber struts have been added to the caissons till all
are now said to be equal to more than double the
weight which a full spring tide can bring against
them. From this space the mud has been flushed
out, and here in this space next week the labour of
building the Embankment proper will begin. The
first operation will be to clear out all the shingle
a depth of 14 feet behind the cais-
and gravel to
sons, or more than 40 feet below high-water mark,
additional and still more powerful timber sup-
ports being added to the caissons as the men
get lower down beneath the river, and the pres-
sure of the great mass of water overhead in-
creases. This somewhat hazardous work will be
done in short sections at a time, and as fast as the
required depth is reached—that is to say, on a level
with the concrete with which the caissons are half
filled—the excavation will cease, and the space is
then to be filled up rapidly with solid concrete. Onhe
this will be laid the brickwork, and over all, on the
river face the solid blocks of granite, which are to
rise in a.massive wall to a height of 30ft. above the
river. It may give a good rough general idea of the
gigantic proportions of this work if we merely men-
tionquantities with which Mr. Furness, the con-
tractor for the first portion only, *from Wes, tnuns. ter
to Waterloo-bridgeeartloads of eartil;as has to deal. First, then, 71,000
to be excavated, and 60,000
cartloads of concrete
70,000 tve
onsteofbetipped
30,000
to
rods, or nearly in," 4,000
brickwork have to' be
laid and faced with
be fils
led ofci granite, and the
whole has afterwards to
400,000 cartloads of earth.
lwho are now
To those behind with
so often blocked up in the Strand bythese slow-
moving, dismal string of carts laden with g'
tidings that at the
earth for
the Embankment it will be sorry
least 200,000 more cartloads have yet to Pass that
way. We fear, however, that the nuisance is una-
voidable. It is not, as in the case of a railway em-
bankment, where a tramway takes any quantity of
earth from one end of the line where it is to be got
to the other end where it cannot be got at all. In the

case of the Embankment both ends are equally in

want of earth, and none is to be had of any sort but
• what the contractors buy in different parts of London,
and this ever-varying quantity, of course, can only
' be brought in carts, and the carts can only come
along the Strand. For the present, therefore, we
fear that an abatement of this nuisance, however