Autobiography of Sir John Rennie, F.R.S., Past President of the Institute of Civil Engineers. Sir John Rennie
I therefore felt highly gratified with this great mark of confidence, and devoted my whole energies to the work night and day. The ironwork was carried into effect by Messrs. Walker, of Rotherham, under the able management of their experienced and able superintendent, Mr. Yeats, and the masonry and piling under the well-known contractors, Messrs. Jolliffe and Banks; and Mr. Meston, the resident engineer, faithfully discharged his duties.
As these arches were the largest of the kind ever constructed, considerable doubts as to their stability occurred to many, and the subject was discussed amongst scientific men with considerable energy; and amongst others, the celebrated Dr. Young undertook to investigate Mr. Rennie’s calculations, and came to the conclusion that the bridge was well designed, and would be a perfectly safe and stable structure, and equal to the support of any weight or amount of traffic which could be brought over it. But in order to fulfil these conditions, it was absolutely necessary that every detail of materials and workmanship should be worked out with the greatest skill and accuracy.
As the arches were of such great span with so small rise, the pressure upon the piers and abutments was chiefly lateral; it therefore became necessary to construct them in such a manner that they should offer the most effectual resistance to this pressure. In consequence, the foundations of the abutments were made on an incline, and the masonry from thence upwards to the springing of the arches was made to consist of a series of courses radiating upwards until they reached the angle of the springing courses; so that, in point of fact, the abutments formed, as it were, a continuation of the side arches to their base; and in order to connect the courses of masonry more solidly together, the courses were connected with each other from the top to the bottom by several series of vertical bond stones, thus forming one solid immovable mass. These abutments were supported on a platform composed of piles, double sleepers, and planking, the piles being 20 feet long, 12 inches in diameter in the middle, and driven solidly into the ground at right angles to the inclination of the foundation. As the pressure upon the piers was nearly equal on both sides, it was necessary that the foundations should be laid level. These also rest upon a wooden platform of double sills and planking, lying upon piles of the same dimensions as those of the abutments, driven vertically into the ground below, and the courses of masonry, which were laid horizontally, were connected together in the vertical direction by a series of bond stones in a similar manner to those of the abutments. The abutments and piers were founded many feet below low-water mark of spring tides, so as to be below the reach of any possible scour of the river. Those parts of the piers from immediately below the springing of the arches to a point above the top of the main solid ribs of the arches were composed of large blocks of stone set nearly vertically, breaking bond laterally and vertically with each other, and in the centre of this part of the piers there was a set of keystones 12 feet long and 2 feet thick, tapering on each side, forming so many stone wedges. These were very finely worked on all sides. These wedge stones broke bond laterally with the blocks in front of them, and were firmly driven into their places for a depth of 2 feet by means of heavy wooden rams. The masonry of the pilasters and salient angles of the piers is of the same character as those of the interior of the pier before described, and worked into them in the same manner, so as to form one solid bond from one point of the pier to the other. The whole of the exterior of this part of the piers, as well as of the abutments, is cased with granite from Scotland or Cornwall; and it was necessary that the blocks forming this casing should be of the largest kind, which hitherto was quite unusual, particularly for the facing of the abutments from whence the arches were to spring, which required blocks from 15 to 20 tons. These were of such unusual magnitude, and nothing of the kind had hitherto been used in London, or even elsewhere in England, that the contractors made considerable objection to obtaining them, and even went so far as to say that it could not be done. I was perfectly convinced that it could be done, and that it was merely a question of a little extra expense, and strongly recommended my father to insist upon it, as it was absolutely necessary for the security of the bridge; and he did so, and directed me to proceed to Aberdeen for the purpose of obtaining them. I accordingly started for Aberdeen; and when there, carefully examined all the quarries in the neighbourhood, which I found had only been opened up on a small scale, and were merely adapted for getting paving stones, the commerce of which with London was then upon a considerable scale; but the idea of obtaining blocks of the size required for the Southwark Bridge was considered to be entirely out of the question; or, even if they could be obtained, the price would be such that the contractors would not consent to pay. In fact, so many difficulties and objections were made that I found nothing could be done in that quarter. I therefore determined to proceed to Peterhead, 30 miles farther northward, where the red granite abounds in large masses near the coast, and where I was told that I should probably succeed; but still, they said, even there it would be very difficult to get them. Upon arriving at Peterhead I immediately set to work exploring the adjacent country for several miles round, and soon found that blocks of the size required could readily be obtained, and even larger ones if necessary. I accordingly selected, by way of experiment, a mass of solid rock about four miles to the south of Peterhead, lying within a quarter of a mile of the sea coast, and about 200 feet above the main turnpike road to Peterhead, which ran along the sea shore. This block, weighing about 25 tons, was accordingly marked out, and was soon detached from the main mass of rock by means of wedges, and was 10 feet long and 5 feet square. The workmen who executed this task were rewarded with ample wages and a good supply of whisky, and were extremely proud of their achievement. Then came the important question, how they were to convey it to Peterhead. To get it to the turnpike road was soon accomplished by means of a wooden inclined tramway formed of stout planks moved upon wooden rollers. Good wages and whisky settled this, and the workmen considered it a further great triumph; but still the greater difficulty remained, how to get this vast block (as it was then considered) four miles to Peterhead. I then went back to Peterhead, and after numerous inquiries, and as many failures and objections on all sides, at last found two large single bogies, each consisting of a pair of strong wheels 8 feet in diameter, connected by a strong axle shaft and a double pair of shafts in front. These two pairs of wheels I joined together at the axle shafts by two strong beams, cased with wrought iron, and strengthened the wheels and axles in other respects as far as necessary. I then took this carriage to the block of red granite already mentioned lying in the road, and slung the stone, by means of strong chains, to the two longitudinal bearers of the carriage. Some twelve or fourteen horses were then attached to the carriage, and off we departed in great triumph for Peterhead. The toll-keeper, never having seen such a mass of stone before, did not know what to charge. However, having at length satisfied his demand, we proceeded onwards, and we had scarcely advanced a mile when we came to a soft piece of road, which yielded under the great weight of the stone, and the wheels stuck fast, buried about 9 inches in the ground. This accident created general dismay amongst the attendant workmen, and they began to consider the task hopeless. However, nothing daunted by this mischance, I soon rallied their courage, and with plenty of screw-jacks, wedges, and levers judiciously applied, we raised the wheels out of the ground, and placed strong wooden beams under them, forming a rough kind of railway, over which we dragged and pushed the carriage with its stone in safety, until we had passed the unsound part of the road. This operation detained us about a day. Everybody worked with the greatest ardour and goodwill, which was aided not a little by a plentiful supply of ale and whisky, and the men were determined, for the honour of Scotland, that they would not be beaten. Having overcome this serious obstacle, we started again on our journey, and reached Peterhead about four hours afterwards, making the total length of the journey—four miles—a day and a half. The whole town of Peterhead, having never seen such a sight before, and having considered our task impracticable, turned out to see us, and welcomed us with the most enthusiastic acclamations.
The next thing to be done, having succeeded so far, was to get a vessel that would take this monstrous block of stone, as it was termed, to London; and although there were a considerable number of vessels in the harbour, I could not at first prevail upon any of the captains to take the charge. All sorts of objections were made, and amongst the rest, it was impossible to get the stone on board, and if they did, it would make a hole in the bottom, and the vessel would founder with all on board. At last, after a great deal of difficulty, I found a brig of about 200 tons burthen, the captain of which, after a good deal of persuasion, consented to take the block of stone to London, provided that I would put it on board at my own risk and expense, and indemnify him against all risk