London and Its Environs Described, vol. 6 (of 6) / Containing an Account of Whatever is Most Remarkable for Grandeur, Elegance, Curiosity or Use, in the City and in the Country Twenty Miles Round It

by Anonymous

The centre arch is seventy-six feet wide, and the others decrease in width four feet on each side, so that the two next to the centre arch are seventy-two feet wide, and so on to the least of the large arches, which are each fifty-two feet wide, and the two small ones in the abutments close to the shore, are about twenty feet in width.

The foundation of the bridge is laid on a solid and firm mass of gravel which lies at the bottom of the bed of the river; but at a much greater depth on the Surry, than the Westminster side; and this inequality of the ground, required the heights of the several piers to be very different; as some have their foundations laid at five feet, and others at fourteen feet under the bed of the river. The piers are all four feet wider at their foundation than at the top, and are founded on the bottoms of the above mentioned wooden cases formed of the most substantial work, eighty feet in length, twenty-eight in breadth, and these timbers are two feet in thickness. The caisson or wooden case, in which the first pier was built, contained an hundred and fifty loads of timber; and forty thousand pound weight is computed to be always under water in stone and timber.

Westminster Bridge.

S. Wale delin. B. Green sc. Oxon.
Walton Bridge.

The materials are much superior to those commonly used on such occasions: the inside is usually filled up with chalk, small stones, or rubbish; but here all the piers are the same on the inside as without, of solid blocks of Portland stone, many of which are four or five tons weight, and none less than a ton, except the closers, or smaller ones, intended for fastening the others, one of which has its place between every four of the large ones. These vast blocks are perfectly well wrought for uniting; they are laid in Dutch terrace, and also fastened together with iron cramps run in with lead. All this iron work is however entirely concealed, and so placed that none of them can be affected by the water.

It is also worthy of remark, that the soffit of every arch is turned and built quite through with blocks of Portland stone, over which is built and bonded in with it, another arch of Purbeck stone, four or five times thicker on the reins than over the key; and by this secondary arch, together with the incumbent load of materials, all the parts of every arch are in equilibrio, and the whole weight so happily adjusted, that each arch can stand single, without affecting, or being affected by the other arches. In short, between every two arches a drain is contrived to carry off the water and filth, that might in time penetrate and accumulate in those places, to the great detriment of the arches.

Though the greatest care was taken in laying the foundation deep in the gravel, and using every probable method to prevent the sinking of the piers, yet all this was in some degree ineffectual, for one of them sunk so considerably when the work was very near compleated, as to retard the finishing it a considerable time. This gave the highest satisfaction to those who had opposed this noble work: but the commissioners for building the bridge, immediately ordered the arch supported by that pier, on the side where it had sunk, to be taken down, and then caused the base of the pier to be loaded with incredible weights, till all the settlement that could be forced was made. After this the arch was rebuilt, and has ever since been as secure as the rest.

In short the last stone was laid in November 1747, eleven years and nine months from the beginning of the construction; a very short period, considering the vastness of the undertaking, the prodigious quantity of stone made use of, hewn out of the quarry, and brought by sea; the interruptions of winter, the damage frequently done by the ice to the piles and scaffolding, and the unavoidable interruptions occasioned twice a day by the tide, which for two years together, reduced the time of labour to only five hours a day. The expence of erecting this bridge, and of procuring all the requisite conveniences was defrayed by parliament, and amounted to 389,000l. which was raised by several lotteries.