432
HISTORY OF ENGINEERING.
Book I.
Masonry in the superstructure.
To 15,850 feet sup), in the soffite of the main arches, being 3 feet thick, £ $.
set in place and mortar included, at 20c?. - 1320 16
To 2000 feet supl. in the soffite of the abutment arches, at Is. - - 100 0
To blocking up the spandrills of the arches solid 6 feet high, containing
473 cube yards, at 5s. - - - - - -118 5
To cube masonry in the spandrill walls, abutments, and wing-walls, fromthe top of the piers to the top of the cordon, containing 3776 yards,at 5s. ------ 944 O
To hammer-dressing the plain superficies thereof, containing 33,984 feet
at 1 }/l. - - - - - - 212 8
In the'parapet, 11,856 feet supl. on both sides, being 15 inches thick, stone,
workmanship, mortar, and setting ditto, at 6d. - 269 8
To 18,382 feet supl. in the faces of the arches, bands and keys, the cordon,mutules, capping, and pedestals, which being before reckoned in solid,except their projecting parts, and all square work, at 4 d. - - 306 7
To 2160 feet supl. in the 12 eyes, and 640 feet in the terminating pillars,in the whole 2800 feet supl. of circular work (being before includedin the solid), at 6d. - - - - - 70 0
The walking path, being 4 feet wide, contains 3641 feet supl. of stone,
working and laying, at Id. ------ 106 12
To 10,948 cube yards, to fill up the spandrills and wing-walls, and form
the road, at 9d. - 410 11
Contingencies.
To piling engines, pumps, and other utensils, supervisal, unforeseen acci-dents, and expences ------ 1000 0
Abstract.
To cofferdams -Excavations and drainageMasonry in the piers and abutmentsCentering for the archesMasonry in the superstructureGravelling the bridgeContingencies - - -
726 2
544 8
- 1840 3
- 1754 10
- 3447 17
410 11
- 1000 0
Total - - - £9723 11
d.
8
O
O
0
o
o
'4
o
0
0
0
0
0
0
1
0
0
0
0
1
In the batterdcaus and centres there remained at least 5763 cube feet of timber, whichif sold at 9c?. per foot cube would amount to 2147. 2.9. 3c7., besides iron work, engines, andutensils; which, it was presumed, would be sufficient to make the road to and from thebridge.
The prices in the preceding estimate include all labour, carriage, mortar, and setting upin place, unless otherwise particularly expressed.
Description and method of fixing the foundation of the second pier and the cofferdam. —The gravel proving harder than was expected in this last pier, much time being occupiedin driving the piles of the cofferdam down to their proper depth, and so much difficulty beingexperienced in drawing them, that they were severely injured when drawn, it was proposedthat for this pier there should be as many additional piles, .as should set the whole at thedistance of 9 feet from the sheeting of the base of the pier, and that they should be drivenno further than to fix them firmly in the ground, even should that happen at only 2 feet.
To prevent the filtration under the bottom of the piles, gravel and corn-mould earthwere thrown in on the outside, after being well mixed together; and this was slopedagainst the piles, and extended to a width of 6 feet all round.
Method of forming the excavation -The pumps being fixed, and the water pumped out,
the excavation was made to the size of the pier; and after having got down a space in themiddle to its proper depth, the width and depth were increased, till the area was clear fordriving the piles, upon which the foundation frame was to rest, and no more, leaving thematter on the outside of the area to form its own slope towards the cofferdam, so that therest of the area remained solid, to support the sheeting of the dam.
The depth of the excavation was determined after the following rule. It must be exca-vated at least 3 feet at a medium below the natural surface of the gravel where the pierstands ; but if this did not carry down the base of the pier within 2 feet of the level at which