The evening telegraph. [volume] (Philadelphia [Pa.]) 1864-1918, 1867-09-17
The New BIackfriars Bridge across the
Thames.

The East River bridge enterprise Gives addi-
tional interest TO the following account of the
new BaCktrlars Bridge over the Thames, which
we copy from the London Ttmes:-
- As the works connected with Blackfriars
Bridge slowly advance, II is tOun1 thatfthe very
causes which fastened the decay of the old
structure are precisely those which are hinder
ing the completion of the new. 1t was the
gradual alteration in the depth of the bed of the
river which destroyed the old bridge. The rush
on its centre and southern piers was too much
for the weak foundation which upheld them,
and though the structure did stand more than
century, nearly halt this period was passed in
sinking slowly, but surely, into a state of hope
less dilapidation and decay. In spite of all the
expensive remedies applied, nothing could re-
store it, and, in fact it was allowed to stand
long after it was dangerous for public traffic:
ITO understand the way 10 which these piers
are built and indeed, most bridge piers are
built nowadays, may not be unInteresting. In
almost every sort of great engineering, archi-
tectural or nautical undertaking, wood has given
place to iron. Wooden cotferdams for piers OF
bridges would be as much out of place now as
wooden sailing ships or mail boats. Wrought
iron caissons for this purpose of bridge building
are purely English invention, though the
name is French. The piers of New Blackfrars
Bridge are each one hundred and ten feet long
by twenty-five feet wide. Instead of building
method OF damming out the river by Golfer
dam Of piles, they are constructed by means of
wrought-iron caissons, six caissons being re-
quired for each pier. These caissons are
simply square wrought-iron tubes open at both
ends, and strengthened inside with iron girders
10 resist the pressure OF the water. They are
sunk on end in row exactly the length of the
pier and on the spot where the pier is to be
built. There are valves in them which allow
the tide water to enter and leave freely as il
falls and rises, and so in few days the great
weight of the caisson all resting on its lower
edge sinks it deep into ali the river mud, gene
rally down to the waters surface, where it will
go no further.
Another rim or tube of wrought iron is then
bolted on to the top of the caisson, and the
girders round the inside of this weighted with
iron ballast to the amount of about one hun
dred tons, and this generally takes it some ten
feet or twelve feet deeper. AT all events, as
long as the caisson continues to sink, other
rims are bolted to it, and other weights added
till it will go no further. In this state it is
generally suffered to remain a week or so,
when the last weights which the iron will bear
are added, and this final test generally sinks it
a few inches deeper. All then is secure, for by
that time. the end of the tube Is as deep as 1t
will 60 into the London clay, and far below
the bed of the river. What has to be done then
is very simple. The water is pumped out OF the
tube by steam-pump in a lew hours, and its
lower end being perfectly sealed by its penetra-
tation into the soil, keeps it perfectly dry. The
mud and ooze which 1T has enclosed are dredged
out down to the clay, and when this is reached
and levelled the work of building the founda-
tion is commenced some fifty feet below the sur
face of the Thames, but still in open daylight
and in perfectly dry and safe chamber.
'The foundations are laid in the hardest
brick, set in concrete, and thus built, the piers
are solid from end to end up to within six feet
of granite commence in huge blocks weighing
f1om twelve TO fifteen tons each, and these are
continued up to the height IRON which the iron.
work of the arches springs.
! 1.-THE caissons have been weighted to the
utmost they will bear with safety, and the sink
ing goes on, but in such an uncertain and
| erratic manner as clearly shows the rotten and
! unsafe nature of the soil through which they
are passing. Thus, for days they may remain
| immovable or only sink an inch or so, while
Vlvv 4lAaxrw 1arr into
in single night. OF course until they have
taken their bearings, as it is called, and will go
no further, nothing can be done, tor to pump
the caisson out with its lower end still insecure
would be only inviting such rush of water be
meath it as would again double the labor to be
gone through to clear 1T.
Notwithstanding the depth of water in the
caisson, the divers, to the number of five, are
| daily at work in it, dredging out the interior of
the tube and sending immense quantities of soil
to the'surface. Their reports all tend to show
that the bottom of the tube is very near the
clay, and that few feet more of penetration
viii make its lower end perfectly water-tght.
In the meantime other portions of the works are
carried on with all the speed that is possible.
"While removing one of the Surrey piers two
foundation stones of black slate were brought to
light One Of them is evidently stone that was
laid with all pomp and ceremonial, while
the other and smaller one found near it was as
evidently slowed away on the same day, but
pror to the ceremonial, by some master work
man, who took advantage OF his opportunity to
| hand down his name to posterity. The clear cut
inscription on the first says:-
"On the 28d daY of June, l76l in the first year o.
the reign of King George III. the tr,t stone of this
the first pier laid by Sir Robert Ladbroke
and presds mt of the hon rable committee carry
ing this bridge into execution. Robert Mylne Rrchi
tect; Joseph Dixon, mason
'The second stone says:-
"'On the 2Sd day OF June, l76l,in the first year o
reign of King George III, the first OF thi
pier was laid by Joseph Dixon, master mason to thi
bridge.
at is more than probable that the last men
toned stone was really that which WAS frs
laid.n