A R C H I T 
and not merely under each pier; and this they did, not by 
/hutting out the whole river at once by one tingle inclofure, 
but by fil'd excluding one part, then another, and to join¬ 
ing the whole together by degrees : for it would be impof- 
fible to withfiand and repel the whole force of the water a-t 
once. We mutt therefore, while we-are at work on one 
part, leave another part open for a paffage for the dream. 
You may leave thefe pafiTages either in the channel itfelf, 
or, if you think it more convenient, you may frame wooden 
dams or- hanging channels, by which the fuperfluous wa¬ 
ter may run off: but, if you find the expence of a conti¬ 
nued foundation for the whole bridge too great, you may 
only make a feparatc foundation for every particular pier, 
in the form of a (hip, with one angle in the (tern and ano¬ 
ther in the head, lying diredlly even with the current of 
the water, that the force of the water may be broken by 
the angles. We are to remember that the water is much 
more dangerous to the (tern than to the head of the pier. 1 ’ 
Palladio, who is the next writer, fays, “ To lay the foun¬ 
dations of pilafters, if the bed of the river be (tone, or gra¬ 
vel-done, you have the foundation without any trouble ; 
but, in cafe the bottom be quickfand, or gravel, you mult 
dig therein till you come to (olid or firm ground; or, if 
that diould be found too laborious or impracticable, you 
mud dig moderately deep in the fand or gravel, and then 
you mud.thrud in oaken piles, which will reach the (olid 
or drm ground, with the iron by which their points are to 
be armed. A part only of the bed of the river mud be 
inclofed from the water, and then vve are to build there ; 
that the other part being left open, the water may have its 
free current; and fo go on from part to part.” 
Scamozzi propoles three different methods; the fil'd:is, 
by driving a double row of piles, and filling in between 
them chalk, or fome clofe materials, and afterwards pump¬ 
ing out the water, and then driving other piles within 
thefe to form the foundation of the piers. This being 
done, a platform of oak-plank is to be framed and laid 
tipon thefe piles, on which the done-work of the pier is 
to red. His fecond method is : after having founded the 
river and levelled its bed, he propofes to make a drong 
oaken-frame, or grillage, which is to be buoyed up with 
boats, and laying on it a thick dratum or layer of dones, 
well cramped together with iron, and jointed with drong 
terrace-mortar, he directs it to be let down gently to the 
bed of the river. The third method is as follows : after 
having turned oft' the courfe of the river to one dde, by 
means of fences or channels funk on one dde of the bed 
of the river, he made a dam with piles entirely acrofs the 
fiver, fufficiently wide to form the piers in; and, when lie 
had by digging obtained a proper foundation, he proceed¬ 
ed to build all his piers together, and, having railed them 
above low-water mark, he again turned the channel of 
the river into its former place. 
It evidently appears, on the face of this author’s ac¬ 
count, that the various circtuudances attendant on rivers 
gave occadon to thefe three methods in the courfe of his 
praClice, and not that he conddered any one of them as 
alike practicable in all cafes. His fil'd method, we pre- 
fume, was applied in thofe cafes where a river was deep, 
and deditute of a natural good bed. His fecond was pro¬ 
bably adopted when a river was moderately deep, but of a 
natural good foundation in its bed, and capable of fupport- 
ing a heavy pier, founded on a drong frame of oak im¬ 
mediately let down upon it, without the infinite trouble 
of piling, damming, and pumping off the water. His 
third fcheme we fuppofe to have been applied in fordable, 
(hallow, and narrow, rivers, canals, or brooks, &c. where 
there was a fuitable place for turning the courfe of the 
water, either by a wooden fence placed in a diagonal or 
(loping direClion acrofs the river, or when the ground on 
one dde of the river formed a pcninfula, or fomething ap¬ 
proaching to it; in which cafe, by digging through the 
neck of land, it was eafy to turn off the dream to one dde, 
and equally eafy to bring it back again. Mod of the 
French bridges have been built on the principles of Sca- 
Yol. II. No. 6r. 
E C T U R E. t2 5 
mozzi’s fil'd method, viz. by driving oak piles and keep¬ 
ing off the water ; this they call a batardeau, and we name 
it a coffer-dam. 
The piers of Wedminder-bridge were founded by an 
improved kind of coffer-dam, made capable of floating 
and riling again after being funk witli two or three of the 
fil'd courfes of done for the pier. The bed of the river 
being of the bed kind, they had little more to do than to 
level it; for previous to this operation, they had driven 
in large piles all round, about dve feet clear of the dimeii- 
dons of the coder-dam. Thefe piles ferved both as a de¬ 
fence to t he coffer-dams, and to fecure them in their place 
when funk. Having laid the drft courfe of dones on the 
bottom of the coffer-dam, they drew it exactly over the 
place where it was to be funk, and, by opening a duice 
made for the purpofe in the dde of this veil'd, the water 
came in and funk it. During about two hours before low- 
water mark, they employed their pumps to draw off the 
wateragain, by which means the coffer-dam was once more 
raifed to the furface, fo as to afford them an opportunity 
of correcting Inch uneven parts of the foundation as they 
might have ubferved in their experiment. To the fil'd: 
courfe they now added two more, cramping each done to¬ 
gether, and filling every joint with terrace-mortar; and, 
after having fo done, they again opened their duice and. 
funk the machine, and depodted the done-work in the 
manner juft related. By this means they foon brought the 
work to within two feet of low-water mark, and by the 
next tide they were enabled to get above it. The fides of 
the cofter-dam were fo contrived, that, by relieving a 
number of iron-wedges, they detached themfely.es from 
the bottom, and were at liberty to be nled for another pier, 
by being again fixed to a new bottom. It fhould alfo be 
obferved, that when the tide was at its height, the cofter- 
dam was about fix feet under the furface of the water; 
but, being loaded with three courfes of dones, and well 
fecured by ropes fadened to the piles, it remained unmo¬ 
ved by the tide. Here it will be very natural to enquire 
why the coders were not made fufficiently deep to exclude 
the water at its greateft height ? The anlwer is eafy, when 
the circumfiances are known ; for, if it be conddered, that 
the water at its full height rofe fixteen feet, and that tljf 
bed of the river where the pier flood was funk about fix 
feet, a coffer twenty-two feet high would have been requi¬ 
red, a fize completely unmanageable; and, as they alfo 
had a duice in the fide of the coffer jud on a level w ith 
low-water mark, and by which all the fuperincumbent 
water was eafily got rid of, it was evidently unneceffary to 
have the coder higher than fixteen feet. The circumftan.ce 
of the coder’s being fo much under water, far from im¬ 
peding, rather facilitated, the execution of the work ; for 
all the water above the edges of the coffer cleared itfelf 
with greater facility than that within, which paired through 
the fluice. As for the remaining wateu-below the duice, 
it was carried off by a number of chain-pumps, fo that 
the workmen were diortly enabled to bring the pier above 
water. 
In the year 1753, the foundation of Effex-bridge in 
Dublin was laid in a very deep and rapid dream by Mr. 
Semple, who adopted the following method: Round the 
place where the intended pier was to red, the workmen 
drove, at about thirty inches didance from each other 
both ways, two rows of drong piles, which were left at 
the height of low-water mark. Thefe piles were lined 
with planks, within which they rammed a quantity of clay, 
and thus formed the external wall of the coffer-dam. 
Within this wall, and at about the fame didances, they 
drove in a row of piles dove-tailed at their edges fo as to 
receive each other, and which formed the extremities of 
the plan of the piers at the level of the bed of the river. 
After having dug to a fine ftratum of fand about four feet 
lower, within thefe there were a great number of other 
piles driven as deep as they pollibly could be made to pe¬ 
netrate. They next filled up the voids or intervals of thefe 
_piles; and, in order to produce a folid and petrified foun- 
K k datioiij 
