Читать книгу The life of Isambard Kingdom Brunel, Civil Engineer - Brunel Isambard - Страница 6

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BIRTH OF MR. BRUNEL, APRIL 9, 1806—SIR MARC ISAMBARD BRUNEL—THE BLOCK MACHINERY—MR. BRUNEL’S SCHOOL LIFE—THE THAMES TUNNEL—SINKING OF THE ROTHERHITHE SHAFT—DESCRIPTION OF THE SHIELD—EXTRACTS FROM SIR ISAMBARD BRUNEL’S JOURNALS FROM THE COMMENCEMENT OF THE THAMES TUNNEL TO THE DATE OF THE SECOND IRRUPTION OF THE RIVER, JANUARY 12, 1828—NOTE A: THE BOURBON SUSPENSION BRIDGES—NOTE B: EXPERIMENTS WITH CARBONIC ACID GAS.

Isambard Kingdom Brunel was born on the ninth day of April, 1806, at Portsmouth, and was the only son of Sir Marc Isambard Brunel.[1]

Most biographies commence with an account of the parentage of the person whose life is about to be written. If this be permitted in any case, no apology can be needed for prefixing to a Life of Mr. Brunel some particulars of his father’s career, since he was indebted to him, not only for the inheritance of many natural gifts, and for a professional education such as few have been able to procure, but also for a bright example of the cultivation of those habits of forethought and perseverance, which alone can ensure the successful accomplishment of great designs.

Sir Marc Isambard Brunel was a native of Hacqueville, a village in Normandy, where his family had been settled for several generations. He was originally intended for the priesthood; but, as he showed no inclination for that calling, and a very decided talent for mechanical pursuits, he was permitted to enter the French Navy; and he served in the West Indies for six years, namely, from 1786 to 1792. On his return home, at the expiration of his term of service, his strong Royalist sympathies made it unsafe for him to remain in France, and with great difficulty he managed to escape to America. He landed at New York in September 1793, and soon obtained employment as a civil engineer. A few years afterwards he was appointed engineer to the State of New York; and, while holding that office, he designed a cannon foundry and other important public works.

In January 1799, when Sir Isambard was in his thirtieth year, he came over to England, and shortly after his arrival married Miss Sophia Kingdom, a lady for whom he had formed an attachment some years before.[2]

The first great work undertaken by him in this country was the machinery for making blocks, which he designed and erected for Government at Portsmouth.

The history of the invention and construction of this system of machinery (for it consisted of forty-three separate machines) need not be given at length; but it may be permitted to extract the following passage from Mr. Beamish’s ‘Life of Sir Isambard Brunel’ (pp. 97, 99, 2nd edition), in which he points out the benefits which have resulted from its introduction, and the position its inventor is entitled to hold among those who have contributed to the progress of mechanical science.

Where fifty men were necessary to complete the shells of blocks previous to the erection of Brunel’s machinery, four men only are now required, and to prepare the sheaves, six men can now do the work which formerly demanded the labours of sixty. So that ten men, by the aid of this machinery, can accomplish with uniformity, celerity, and ease, what formerly required the uncertain labour of one hundred and ten.

When we call to mind that at the time these works were executed, mechanical engineering was only in its infancy, we are filled with amazement at the sagacity and skill that should have so far anticipated the progress of the age, as to leave scarcely any room, during half a century, for the introduction of any improvement....

Beautiful as are the combinations and contrivances in the block machinery, and highly deserving as the inventor may be of credit for originating such labour-saving machines for the production of ships’ blocks, there is a far higher claim to the admiration and gratitude of all constructors of machinery, and of all workers in metal. In this block machinery exist the types and examples of all the modern self-acting tools, without the aid of which the various mechanical appliances of the present day could not be produced with the marvellous accuracy which has been attained. It is true that to the trades unions or combinations among the artisans, is in a great measure directly due the introduction of self-acting machines; but the types of all these tools existed in the machines and combinations of Brunel’s block machinery. The drilling, the slotting, and the shaping machines, the eccentric chuck, and the slide rest, with the worm wheel motion, are all to be found in his machine.

On the completion of the block machinery Sir Isambard Brunel removed to London, and took a house in Lindsay Row, Chelsea, where he remained until he was obliged to live nearer the works of the Thames Tunnel.

Mr. Brunel’s first recollections were of the house at Chelsea; and in 1814, when he was eight years old, he commenced his school life under the Rev. Weeden Butler, who resided in the neighbourhood. Previously to his going to Mr. Butler, he had been taught Euclid by Sir Isambard; and he had also a great talent for drawing, for which he had been remarkable even from four years old. His drawings were beautifully precise and neat, but, when the subject admitted of it, full of vigour and picturesque effect.

After some time he was sent to Dr. Morell’s school at Hove, near Brighton. The following extract is taken from one of his letters home in 1820:—

I have past Sallust some time, but I am sorry to say I did not read all, as Dr. Morell wished me to get into another class. I am at present reading Terence and Horace. I like Horace very much, but not as much as Virgil. As to what I am about, I have been making half a dozen boats lately, till I have worn my hands to pieces. I have also taken a plan of Hove, which is a very amusing job. I should be much obliged to you if you would ask papa (I hope he is quite well and hearty), whether he would lend me his long measure. It is a long eighty-foot tape; he will know what I mean. I will take care of it, for I want to take a more exact plan, though this is pretty exact, I think. I have also been drawing a little. I intend to take a view of all (about five) the principal houses in that great town, Hove. I have already taken one or two.

In the intervals of his classical studies he seems to have employed himself, not only in making a survey of Hove in its existing state, but also in a critical examination of the works in progress for its enlargement. It is told of him that one evening he predicted the fall, before the next morning, of some houses which were building opposite the school, and laid a bet on the subject, which his companions readily accepted. He had noticed the bad way in which the work was done, and that the stormy weather, which appeared to be setting in for the night, would probably blow the walls down. In the morning he claimed the wager, for the buildings had fallen in the night.

Except from November 1820 to August 1822, when he was at the Collége Henri Quatre at Paris,[3] Mr. Brunel was so very little absent from home that he became thoroughly acquainted with all his father’s undertakings. Among these was the veneering machinery at Battersea, remarkable for the great diameter of the saw, the steadiness of its motion, and the mechanical arrangements for clearing the veneer from the saw; also the works at the Government establishments at Woolwich and Chatham, and the machinery for making shoes. They have been fully described by Mr. Beamish; but the mere mention of their names is enough to show how great were the advantages enjoyed by Mr. Brunel in receiving from his father his early professional education.

From the year 1823 Mr. Brunel was regularly employed in his father’s office. It was in the early part of this year that the project of the Thames Tunnel first began to occupy Sir Isambard’s attention; but he was also engaged at that time in other works of great importance, among them the suspension bridges for the Ile de Bourbon, and designs for bridges of the same character over the Serpentine, and over the Thames at Kingston.[4] Some account of the Bourbon bridges, and also of experiments with carbonic acid gas, on which Mr. Brunel was engaged, will be found in the notes to this chapter.

The history of the Thames Tunnel will be told, as far as possible, in Sir Isambard Brunel’s own words, as given in his journals.[5] Although these extracts do not relate to works for which Mr. Brunel was personally responsible, they have been inserted in the belief that they are valuable, not only as showing the nature and extent of his duties as his father’s assistant, but also as displaying, in the most interesting and authentic form, Sir Isambard’s character and genius at a time when his son was brought into hourly contact with him, and under circumstances which would cause the influence of his example to make a deep and lasting impression.

Previously to the year 1823 there had been several plans suggested for the construction of a tunnel under the Thames; and it would seem that a great demand was supposed to exist for some such means of communication between the two sides of the river eastward of London Bridge; for after the failure of the operations undertaken by Mr. Vasie in 1805, and Mr. Trevethick in 1807,[6] a high level suspension bridge was proposed, although it was not intended to be used for heavy traffic.[7]

The first reference to the Tunnel in Sir Isambard’s journals is dated February 12, 1823. ‘Engaged on drawings connected with Tunnel;’ and on the 17th and following days of the same month, ‘Isambard was engaged on Tunnel.’ These entries become more and more frequent in the pages of his diary, until it is evident that Sir Isambard’s whole time and thoughts were absorbed in this work.

The spring of 1823 was occupied in preparing drawings and models of his plans, and in enlisting the sympathy and assistance of various influential persons. By the close of the year the designs were matured sufficiently to enable the promoters of the scheme to commence the task of organising a company for carrying it out; and in January 1824 they resolved to call a general meeting of their friends, and invite public subscriptions.

On February 17, Sir Isambard explained his plans at the Institution of Civil Engineers, and on the next day a meeting was held at the City of London Tavern, under the presidency of Mr. William Smith, M.P., more than a hundred persons being present. Resolutions authorising the formation of a company were passed unanimously, and the share list was opened. In the course of an hour one-third of the subscriptions was filled up, namely, 1250 shares; and before the end of the day the number of shares taken was 1381.

Borings were then commenced in order to ascertain the nature of the strata through which the Tunnel would pass. A bed of gravel was found over the clay, which gave Sir Isambard great anxiety. A large pipe or shaft was sunk on the side of the river, and in it the water rose to within three feet of the surface of the ground, and fell about eighteen inches with the tide. ‘It is manifest (Sir Isambard writes) from this that unless the Tunnel is enclosed in the stratum of clay, it would be unsafe to drive through the bed of gravel. The Tunnel must, therefore, begin with the substantial clay.’

However, the result of thirty-nine borings in two parallel lines across the river, to the depth of from 23 to 37½ feet, seemed to prove that there was below the gravel a stratum of strong blue clay of sufficient depth to ensure the safety of the Tunnel.[8]

A report to this effect was made to the shareholders at their first general meeting in July, and it was also stated that the works would be completed in three years.

The first operation connected with the works, was the constriction of a shaft; and for this purpose land was bought on the Rotherhithe bank, about fifty yards from the river. On March 2, 1825, the ceremony of laying the first stone of the shaft was performed.

Mr. Smith, our chairman, attended by most of the members of the Court of Directors, and a very numerous cortége of friends invited on the occasion, proceeded from the Tunnel Wharf to the ground, where they were received among the cheers of a great concourse of people. Mr. Smith addressed the assembly in a very eloquent speech suitable to the occasion, and performed the ceremony of laying the first stone. From this day dates the beginning of the work.[9]

The mode in which Sir Isambard decided to construct the shaft was one not uncommonly adopted in the construction of wells; but to apply it to sinking a shaft fifty feet in diameter was a novel and bold undertaking. The brickwork intended to form the lining of the shaft was built on the surface of the ground, and the earth being excavated from within and underneath the structure, it sank gradually down to its final position.

The brickwork was 3 feet thick, bound together by iron and timber ties, and there were built into it 48 perpendicular iron rods, one inch in diameter, fastened to a wooden curb at the bottom, and to another curb at the top of the wall, by nuts and screws.

When the shaft or tower of brickwork was completed up to the top, 42 feet in height, the next step was to remove the blockings on which it rested, and this being done the gravel was excavated and hoisted up, and the shaft descended by its own weight.

The Rotherhithe shaft was only sunk forty feet in this manner; the remaining twenty feet, in order to leave the opening for the Tunnel, was constructed by under-pinning, or underlaying, as it was then termed. The underlaying was commenced in the beginning of June.[10]

By July 4 they had got down to the level of the intended foundation of the shaft, having passed into a stratum of gravel, black pebbles embedded in greenish sand, with little or no water; from which circumstance Sir Isambard was of opinion that it was unconnected with the stratum of gravel above.

July 12.—Engaged on a general drawing for the great shield, and in preparing some instructions for moving the same (a very intricate operation!)

July 22.—Underlaying is a very laborious mode of proceeding. The sinking of a wall well bound as the first, would evidently be the best and cheapest mode for making another tower of 50 feet diameter.

On the 28th Sir Isambard enters in his journal the following additional observations upon the success of his plans for sinking the shaft:—

Considering the great labour necessary for securing the ground for the underlaying, the waste of planking, and of shores, and the time necessarily taken up in moving about, in securing and in baling out the water, and the many causes of interruption, and the imperfect way that things are done in underlaying, it is quite conclusive that the original plan of making a shaft, by sinking the structure, is the safest and the most economical. What is done is sound, and when once in place, may be secured with foundations in a very easy manner. The brickwork of the shaft is remarkably hard. Had it been made with brick facings and rubble stone, it would certainly be water-tight, and almost impenetrable by ordinary ways. The vertical ties and the circular wall bands are not to be dispensed with in a structure destined to be moved as the present has been.

On August 11 the underlaying was completed, and preparations were made for constructing a reservoir in the bottom of the shaft for receiving the permanent pumps. This was finished on October 11, with great difficulty, owing to the nature of the ground, which consisted of loose sand containing a large quantity of water.

August 19.—Engaged at home in revising my plans for the manner of carrying on the horizontal excavation, more particularly of penetrating through the shaft. This part of the operation requires indeed very great attention, as it presents great difficulties, arising from the wall to be broken through, and chiefly from the angular opening that is to be made at each extremity. Then another consideration is the uniting the brick arches to the brickwork of the shaft.

September 16.—Engaged in the early part of the day on revising my plans of future operations in the Tunnel work, and in adapting them to the nature of the ground as it is found at the various depths we have penetrated: namely, to about 73 feet. Went afterwards to Maudslay to request that the great shield may be completed.

Great shield.

October 14.—Engaged in the early part of the morning in making some arrangements for the working of the great shield. Too much attention cannot be given to that subject at the early part; for, when once in its place, it would be extremely inconvenient to make any alteration.

Preparing for the frames.

October 15.—The dome of the reservoir will be covered to-day about noon; the bottom of the shaft will therefore be completed. They are now preparing to apply two frames of the shield. The ground now open in the front is remarkably hard; it consists of pebbles imbedded in a chalky substance, with hard loose stones of the nature of the Kentish rag. Everything is going on well. Devised with Isambard how to make our wells for the descent of the materials, &c.

Thus at last the shaft was completed, and Sir Isambard was able to commence the Tunnel itself, which he ultimately determined to construct in the form of a rectangular mass of brickwork, 37½ feet wide and 22 feet high, pierced by two parallel horseshoe archways, each 14 feet wide and 17 feet high.

Before entering upon the history of this undertaking, some account must be given of the machine which Sir Isambard Brunel devised for effecting its accomplishment.

In order to avoid a quicksand of considerable depth and extent, the Tunnel had to be carried but a short distance below the bed of the river; and, as in all tunnelling through soft soil,[11] the top and sides of the excavation had to be supported until the brickwork was built in; and the front or face had also to be held up as the miners advanced. This support was given by means of a machine called ‘the shield,’ described on one occasion by Sir Isambard as ‘an ambulating cofferdam, travelling horizontally.’[12]

The main body of the shield consisted of twelve independent structures or ‘frames’ made of cast and wrought iron. They were each 22 feet high, and rather more than 3 feet wide; and, when placed side by side, like books on a shelf, against the face of the excavation, they occupied the whole area of the face, and also the top, bottom, and sides for 9 feet in advance of the brickwork. Each frame stood on two feet resting on the ground, and was divided in its height into three cells by cast-iron floors. In these cells, of which there were thus thirty-six in all, the miners stood, and worked at the ground in front of them.

The duty which the shield had to perform was to support the ground until the brickwork was built within the excavation; but it was essential that this should be done in such a manner as to allow of the mining operations being carried on; and it was also necessary that the machine itself should be capable of being moved forward.

The first point, therefore, which has to be explained in the action of the shield is the manner in which the earth was supported by it.

It has been already stated that each frame rested upon two feet, or large iron plates. These two feet together covered the ground under the frame to which they belonged, and thus the whole of the earth beneath the frames was pressed down by the feet.

The earth above was supported by narrow iron plates, called staves, laid on the heads of the frames parallel to the line of the Tunnel, the ends resting on the completed brickwork behind it. The earth at the sides was kept up by staves resting against the outermost frames.

The arrangement for holding up the earth at the face of the excavation was necessarily of a more complicated character. Each frame supported a series of boards called poling-boards, by means of small screw-jacks or poling-screws, two to each poling-board, which abutted against the frames, and pressed the boards against the earth. The boards were 3 feet long, 6 inches wide, and 3 inches thick, and were arranged horizontally. These poling-boards, more than five hundred in number, covered the whole surface in front of the frames.

To resist the backward thrust of the poling-screws against the frames, each frame was held forward by two large screws, one at the top of the frame, and the other at the bottom, abutting against the brickwork of the Tunnel. The brickwork was completed close up behind the shield as it advanced.

The way in which the earth was excavated, and the shield moved forward, has now to be explained.

The plates or staves which supported the ground at the top and sides of the shield were pushed forward separately by screw-jacks; but in order to advance the poling-boards in front, it was necessary that that portion of the ground against which they pressed should be removed.

The miner, standing in his cell, took down one, or, at the most, two of the poling-boards, commencing at the top of the cell, and having excavated the earth a few inches in advance, replaced the poling-boards against the newly-formed face, pressing them against it with the poling-screws. Thus the excavation was carried on without depriving the ground of the support it received from the shield, except at the point where the miner was actually at work.

The operation of advancing the frames was effected in the following way. When everything was ready for a move, one of the feet which carried the frames on jointed legs was lifted up, and advanced forward a few inches, and then pressed down on to the ground, until in its new position it again bore the weight of the frame. This done, the other foot was lifted, moved forward, and screwed down in the same manner, and then the frame itself was pushed ahead by means of the large abutting screws, which kept it top and bottom from being forced back on the brickwork.

It is, however, evident that these abutting screws would have been unable to push on the frame, while the ground in front was pressing back the poling-boards against it; therefore, during the process of moving a frame, it had to be relieved from the thrust of its poling-screws. Accordingly, when it was desired to advance any one of the frames, the butts of the poling-screws of the tier of boards in front of it were shifted sideways, so as to rest, not against the frame to which they belonged, but against the frames next it on either side. This done, the frame itself was advanced, and was then ready to receive again its own poling-screws, and also those belonging to the adjoining frames, so that they might in their turn be moved forward. It will thus be seen that the whole shield was not moved forward at one time, but that the frames were advanced alternately.

There were many other ingenious arrangements in the design of the shield, which need not be referred to in a description intended only to give such a general idea of the machine as may make the history of its operation intelligible.[13]

When the frames had been completed in Messrs. Maudslay’s factory, they were conveyed to Rotherhithe, and lowered down the shaft. An opening had been left at the bottom of the wall, about 37 feet wide by 22 feet high, and against this the shield was erected. It was then ready to commence its progress through the ground below the river.

On November 25, 1825, the shield made its first start. Sir Isambard was unfortunately unable to witness what was in fact the actual commencement of the Tunnel, as he had three days before been seized with a sudden and alarming attack of illness, which kept him at home till December 6. The works were left under the direction of Mr. Brunel.

December 8.—The great shield is advancing very slowly, meeting with much interruption by the water, which still runs within the cells, and also by the difficulty of forming abutments for the frames. [Temporary abutments were necessary until the shield was sufficiently advanced to allow of its being pushed forwards from the brickwork built up behind it.]

December 29.—The frames are very much out of level in the transverse line of the Tunnel. This would be attended with serious inconvenience if I had not provided for the means of recovering any irregularity that might take place, and which, as it appears, cannot perhaps be prevented; but having foreseen this, I have provided the remedy by being able to take down the top of each frame, and to remove the top staves in parts, or the whole, at pleasure—a very important provision it proves to be.

January 16, 1826.—Too much precaution cannot be taken, in the management of the frames, to have the leg-screw particularly well secured, as every foot-run of the arch of the Tunnel sustains 82 tons. Each frame carries as follows:—

The two end frames each	65 tons	= 130
Ten others, each	52½ "	= 525
		655	tons.

January 21.—The ground at the top and sides very good; same in the front. In breaking the ground out of the limits of the shield on the right a great deal of ground fell in. This indicates that, if it was not for the protection of the shield, nothing could be done. This accounts also for the occasional breaking of the ground in making the drift in 1809.

Tunnel begun.

The brickwork of the entrance being carried as far as directed, the body of the Tunnel was begun to-day.

Water broke into the works.

January 26.—Isambard went down to Rotherhithe; the water had broken in in great abundance upon the work over Nos. 4 and 5. [The twelve frames were distinguished by numbers.] A 4-inch pipe was driven over the shield from inside the shaft, but the water did not follow it, and the stream augmented very rapidly. The frame No. 5 was moved forward, and it checked the water for a moment, but it came again with violence. A heading was immediately ordered by Armstrong [the resident engineer] from the east well, in which Isambard concurred.

February 3.—Ordered a pit to be opened and made by sinking a curb 8 feet diameter and 18 inches thick, well bound with bolts. [This pit was a well sunk from the surface to enable the gravel containing water, into which the head of the shield had penetrated, to be removed, and clay substituted.]

February 6.—The shaft begun last night, and was sunk 20 feet to-day, and remarkably true. Had we known the ground as we now know it, we might, by having opened a well contiguous to the great shaft, have sunk the shaft in a week; but for that purpose we must have had two steam engines, one for pumping the water, and the other for taking up the ground.

Unremitted attention wanted.

February 10.—Went very early to the Tunnel for the purpose of giving directions to prop up the back of the staves, which, for want of weight at the new shaft, might be overbalanced by the pressure of the ground at the back. I could not rest a moment until it was done, for the consequences might have been fatal, at this moment in particular. What incessant attention and anxiety! To be at the mercy of ignorance and carelessness! No work like this.

Observations on the mode adopted to check the water.

February 12.—The ground having been opened carefully from under the curb of the pit [see above on date February 3], the greater part of the gravel was removed, and stiff clay substituted for it. This was done by driving first some wrought-iron flat bars, which kept the ground up. This shows that the shield is a most powerful protection, and would enable us to penetrate through a bed of gravel. Though the breaking in of the water had somewhat terrified the man in No. 5, he soon returned to his post, and the others have acknowledged their full confidence in the security afforded by the shield. The boring ahead had not yet been attended to: it is owing to the want of this precaution that this accident is chiefly to be ascribed; for had we known as much as we now do, we might have passed through without the pit being opened.

March 1.—Water at the back of the frames, but less than before. The men show a great deal of spirit in overcoming the present difficulties. Isambard was very busy yesterday and to-day in the frames, and about the works. He was severely hurt in the leg by a piece of timber falling against it. [This accident prevented his attending again at the Tunnel until the 24th.]

On March 6 the proprietors paid a visit to the Tunnel, and were highly satisfied with what they saw. On that evening Sir Isambard writes:—

It is of absolute necessity now to provide for everything that is conducive to the more expeditious management of the frames, and to a greater facility in getting up the brickwork. If these two points are realized, then indeed we may soon expect to be moving at a good rate—not less than I have held out, namely, 3 feet per 24 hours.

Water stopped as expected.

March 11.—Received early in the morning a report from Armstrong stating that the water was completely stopped—that it had been stopped during the night. Aware that we had passed the gravel, it was of course expected that we were under the clay; means were therefore resorted to, to drive clay and oakum at the tail of the top staves, which was productive of a very good effect. The great shield was soon entirely free of water. This shows the efficiency of the shield to oppose difficulties which could not have been overcome without the complete protection it affords, under almost any circumstances. Indeed this has been a tedious operation since January 25, when the water first burst upon No. 5, at the front of the shield. The miners as well as the bricklayers have worked with great spirit and perseverance through the whole, during a period of 44 days. The well that was made at the front of the shaft has been of use in acquainting us with the extent of the open ground we had to pass through. It will be made a useful opening for ventilating the works. By means of this well we have been able to apply the lead pipes with which the water has been diverted: it is not therefore a useless expense. Things were put in better order to prepare for a more expeditious way of working. Directions were given to place the frames in a better condition. Isambard is still too unwell to go to the Tunnel.

Considerable slip of ground: how to check it.

Very dangerous.

March 25.—Went to the Tunnel with Isambard. Found that a considerable fall of ground had taken place again at the right side. No one could account satisfactorily for it. I inspected it, and directed that, after making it good, flat bars of iron be driven at the head of the side staves, in order to pin it up, and in order to enable the miners to get at the solid ground. It is very bad and extremely dangerous; the ground is evidently the same as that which, in the report of the first attempt, was found so loose as to have dropped upon the works, leaving a large cavity above, when it is said the man ascended and made good the hole. We should be warned by this, lest we should meet another as fatal as it ultimately was on that occasion. [This observation refers to the driftway of 1807.]

April 24.—By Armstrong’s report the water is entirely out, and the men at work in the morning in removing the dirt, &c. Isambard engaged at the Tunnel, where I am not yet able to attend as often as I could wish. Everything goes on well, much through his exertions.

May 11.—One hundred feet will be completed to-night.

May 22.—The top plate over the frame No. 1 has been cracked without any particular violence or stress. It appears that it is nothing but the change of temperature that is the cause of that rupture. The accident justifies the opinion I have of cast-iron not being safe upon traction, and the precaution of having had wrought-iron bolts at the back of the frames. [These were vertical rods which took the tensional strain.] Without these bolts what would have become of the shield, if one casting was to break? The fracture was accompanied with a loud report like that of a gun. Isambard was in the works at the time of breaking: nothing could have prevented it.

The shield being too much out, resolved to move it bodily.

May 25.—I observed that nothing whatever had been gained to recover the deviation [the shield had gradually worked 2 feet 3 inches to the westward], which subjects us to so much inconvenience and loss of time. The only way to bring the shield right is by taking the frames sideways.

June 3.—Finding it too laborious and almost fruitless to bring the frames in the right way, I came to the determination of having them brought bodily to the east by cutting the ground on the side. I accordingly gave directions to Armstrong to proceed in making a heading out of No. 12, and by securing the side staves to continue downwards until the ground be clear. The working was accordingly discontinued in front.

June 4.—The mode of proceeding by the common way of mining shows the impracticability of carrying a large excavation anywhere, particularly under a considerable body of water. The expense of timbering would be too great, even if it could be sound. The ground above the frames is remarkably good, but under it there is a stratum of silt which breaks and falls in large masses.

Isambard’s service very important and most efficient.

June 5.—Isambard got into the drift, and gave the line for the better disposition of the staves, which was afterwards done in a proper manner. Isambard’s vigilance and constant attendance were of great benefit. He is in every respect a most useful coadjutor in this undertaking.

June 10.—The last frame (No. 1) is brought close to the others, and the brickwork brought up to fill the back.

Dangerous state of the ground. Precautions taken.

June 15.—On inspecting the face of the ground this morning I observed a breach in the front of Nos. 3, 4, and 5, where the ground has given way in the lower cell. This was truly alarming. I ordered iron staves to each floor in order to pin the ground, and thereby to counteract the slipping which would immediately take place.

June 19.—The bricklayers left off work, but, on enquiring into the cause, I learned there was no other but to have a libation upon the new arrangement of piece-work.

June 29.—Gave positive directions to cut only 4½ to 5 inches thick at a time at the front of the top cells, instead of 9 inches, as they had done for some time.

July 3.—The great question is, does the clay undulate at its surface? We should have some reason to apprehend that it does so, because at the beginning we had not proceeded many feet into the clay when we struck again into the gravelly stratum. The surface of the clay must therefore have sunk at that particular spot; which circumstance seems to warn one of the need of great vigilance and great prudence in the progress of the enterprise.

Cofferdam burst at Woolwich.

Warning for us.

July 10.—A cofferdam burst yesterday at the works at Woolwich, having blown up from the foundation. How cautious this should make our men! The cofferdam may be repaired, and very easily too, but an irruption into the Tunnel—what a difference, particularly at this early period!

Carelessness of the miners.

August 10.—Found the lowest cell of No. 1 left by the workmen without a single poling against the ground. This is indeed a most unjustifiable neglect.

August 12.—At six this morning completed 205 feet.

Observations on the bad effect and consequence of driving on as is done.

August 21.—This piece-work has not been productive of much effect as to quantity of work. As to quality it is very questionable. A work of this nature should not be hurried in this manner. Fewer hands, enough to produce 9 feet per week, would be far better than the mode now pursued from necessity, but not from inclination on my part. Great risks are in our way, and we increase them by the manner the excavation is carried on. The frames are in a very bad condition.

September 5.—It is much to be regretted that such a work as the Tunnel should be carried on by the piece. Obliged to drive on, no time is left to make any repair, or to recover any lost advantage. Isambard is most active. Mr. Beamish shows much judgment in his exertions, and zeal in his attendance.[14]

Water breaking in at back of frames.

How to check it. Isambard’s exertions.

September 8.—About 2 P.M. I was informed by Munday that water was running down over No. 9. I went immediately to it. The ground being open, and consequently unsupported, it soon became soft, and settled on the back of the staves, moving down in a stream of diluted silt, which is the most dangerous substance we have to contend with. Some oakum was forced through the joints of the staves, and the water was partly checked. Isambard was the whole night, till three, in the frames. At three I relieved him. He went to rest for about a couple of hours; I took some rest on the stage.

Things improving.

September 9.—Towards noon the stream changed its character. The clay, being loosened by the water, began to run, but it thickened gradually. It was late in the evening before the loosened clay acquired the consistency of a loose puddling, which covered the staves, and made them a complete shield against further irruption, or rather, oozings of mud. If we consider that at this place we have at the utmost 9 feet between the top staves and the gravel, over which the river flows, it is most satisfactory and most encouraging to have this additional proof of the protection which the shield affords. At nine o’clock at night Isambard sent me word that ‘tout va à merveille;’ indeed it was so, for it was like a stopper interposed between the river and the top-staves. Instructed as the men were by the first accident, they went on as usual in the irrespective occupations. Pascoe, junr., and Collins were remarkably active and persevering, and some other men equally so; while old Greenwell encouraged them by a speech of his own in high commendation of the security of their situation.

Water more abundant. Is it from the river?

September 12.—The water, bringing with it a sort of clay broken in small particles, increased to an alarming degree. In consequence of this continued displacement of the silt and clay, a cavity had been formed above the staves. At about three, when I had gone to the Court of Directors, the ground fell upon the staves with great violence, causing a surge most alarming as to probable consequences. Isambard was at that moment in the upper frames, and he gave directions for increasing the means of security. On my return I found things much worse than I left them, but every means of security was judiciously applied. During the night in particular things presented a very unfavourable appearance. The men, however, were as calm as if there were no other danger to be dreaded than wet clothes or the splashing of mud. I observed the men in the lower cells were sound asleep.

Exertions by the men.

Slight improvement.

September 13.—Every means were resorted to in the course of the night and during the early part of the day to stop the water. The men have shown great zeal and good management in their respective avocations, and above all the utmost confidence. Isambard has not quitted the frames but to lay down now and then on the stage. I have prevailed on him to go to his bed, or rather, used my endeavours to induce him; but he has not since last Friday night (the 8th). Things were rather better at the close of the day.

September 14.—Things upon the whole have assumed a more favourable aspect. The situation is nevertheless very critical. Nothing but the utmost precaution in following up what has begun can bring us out of it. This has been a most eventful week!

September 18.—Isambard was the greater part of the night in the works, and the benefit of his exertions is indeed most highly felt: no one has stood out like him! Everything is quite safe, the water is kept back, and the work proceeds in a most satisfactory manner.

October 22.—It is evident [from a flow of silt which had taken place on that day] that with the shield we have passed close under a body of collected water a few inches only above the staves. Isambard is too unwell to stay long in the works.

The want of a drain subjects us to much inconvenience.

October 24.—The want of the main drain which was originally intended to carry the water to the main reservoir is felt everywhere. This drain is in my original plan, but the committee expressing on several occasions a wish that I should dispense with it, I complied, most reluctantly however, to prove my earnest wish to reduce the expenses. It will not, I apprehend, be found an economy.

Effect of the shoes in keeping the ground dense.

October 26.—Every step we take shows how much security is derived from the shoes, supporting as they do the shield and the superincumbent weight. They press down in the same proportion the ground on which they bear. They keep it as dense as it originally was, and fit it for the structure that is to come upon it. It is evident, therefore, that what is wanted is that the ground should be kept pressed. It is with this object in view that I have holdfasts and jacks. What incessant vigilance is required, what an incessant call on the resources of the mind, not only to direct, but more particularly to provide for many things that may occur.

November 17.—At this date 307 feet 9 inches had been completed.[15]

December 8.—The evil [that of not having a proper drain] is going on with us, and without any remedy except the drain, or a cesspool by way of expedient. How much anxiety must one feel at being so circumstanced! Should any water break in, how should we proceed? This is another source of great solicitude. We have no command of the frames when they rest upon wooden legs, or when the screws are bent; and what is worse is that the men drive on without any consideration or any fear of consequences. This circumstance, and the apprehension of the water breaking in, are matters of the most dreadful anxiety.

Superincumbent weight varying daily, and still more every fortnight. What stress on the frames. The shoes have never yielded; a most important circumstance.

December 12.—Little do others know of the anxiety and fatigue I have to undergo day and night. Advanced as we are, we have only gained somewhat more experience, but the casualties are just the same. An accident now might be as fatal as it would have been 200 feet back, or as it would be 200 feet forwards. We have not a period when we can think ourselves safe except when we have connected these arches with a shaft on the other side. Loaded as we are with the weight of the river, we have to advance our shield and build our structure under that weight, a weight which varies twice a day, and twice a month to a much greater extent. The shoes are the great foundation of our security. When once pressed down with the greatest power that can be applied, they do not give in the least afterwards. They have not yielded even upon loose gravel; we must therefore congratulate ourselves that they have answered so completely. We have now walked our frames upwards of 350 feet; we have had to renew the legs and the heads, but it is not through want of strength so much as from mismanagement. The first legs were never injured so long as their action was limited to 3 inches, but when it was increased to 6 inches, they immediately gave way one after another, without however any damage to the structure or to the shield. The heads gave way, or began to give way, from the moment the legs did; because, when a leg gave way, it brought upon the contiguous frame an increased weight which broke the heads one after another. That the breaking of so important a part of our shield should not have been attended with any bad consequences is a proof that provision had been made for the casualty. The proof that it had been foreseen and provided for is in the manner these heads were adapted to the frames. By the way they were fixed they would be easily taken down and replaced. Though the heads gave way, the top staves were not materially affected by it, and the service continued until new heads were substituted. Some have fancied that the ground did not bear wholly upon the shield and the arches, but supported itself in parts. Experience proves that the pressure is rather more than that which rests artificially on the frames. The ground is compressed all round by the increased weight of high water: we might therefore conclude that the shield operates as a pillar, that supports beyond the limits of its base or cap. It is a great satisfaction to be able to say that so long as we followed the original plan, nothing gave way except the back screws. These again were damaged by being run out of the sockets. We may therefore ascribe most of the evils and damages to the increased range of action, and still more to the rude implements the men have used, whenever they met with any difficulty in moving the frames. If it is considered that we had no other men to train in the use of this immense machine but excavators and miners, very great allowance must be made for what has occurred.

Falling of three facings from neglect. Awful!

December 20.—An accident of an alarming nature occurred. The poling-screws of Nos. 10 and 12, being on No. 11, Moul, the miner in that frame, removed his butting screw; the consequence was that the frame started back, the polings and poling-screws fell down with a tremendous crash, and the ground followed to a considerable extent. This is the most formidable accident that has yet occurred in the face of the work. The ground was fortunately unusually firm, and no fatal consequences ensued.

December 31.—Isambard and nine friends sat down to a dinner under the Thames! Now a year is over since we began to make any progress horizontally, for we had only 11 feet of arch when the water broke in on January 24 last. We may therefore say that the whole of what has been made of the Tunnel has been made in that period. It is worthy of remark that until the end of April no fracture whatever, no bending of the legs, had taken place, notwithstanding that we had supported for a period of nearly three months a greater weight than we ever had since. The ground nearly 40 feet high kept sinking upon us as we advanced, and yet no stave, no top, no leg gave way. Each leg was capable of carrying nearly 80 tons at the point of fracture, consequently the aggregate strength of 36 legs was equal to 2,880 tons, which is six times over the greatest effort that could be exerted by the superincumbent weight. The heads, after they had given way, remained in place, some—namely, Nos. 1, 8, 12—for seven months, and the others from four to six months. It cannot be said therefore that there was a want of strength, since the broken heads continued to perform for so many months after being so much damaged; nor is there any defect in the iron. If the frames were, as some have fancied, lanky, which implies weakness in their sides, how could they have supported the alternate stress to which they are put by standing alternately on one leg? Not one single joint has yet started. Every frame has been upwards of 2,000 times in that raking posture, consequently the shield has been upwards of 24,000 times strained under the weight that has broken the heads. One single side has broken, and is now as good as the rest. Is such a machine to be stigmatised as it has been, without looking more minutely into its operations?

Observations on the responsibility attached to this enterprise.

January 4, 1827.[16]—A work that requires such close attention, so much ingenuity, and carried on day and night by the rudest hands possible—what anxiety, what fatigue, both of mind and body! Every morning I say, Another day of danger over!

January 12.—It is astonishing how the silt resists the sliding of the top staves. Assured as we were of having stiff clay from 33 to 37 feet, with what confidence we might have looked to making 18 feet per week. There would be no difficulty in having accomplished it. We must not look back, but overcome all difficulties!

Isambard on duty several successive nights.

January 16.—Isambard having been up several successive nights, went to bed at ten, and slept till six the next morning. I am very much concerned at his being so unmindful of his health. He may pay dear for it.

February 2.—Work done to this day 405 feet 4 inches.

February 3.—I visited the works; and, being in the cabin, I complained of the dust there. Dust under the Thames!

February 26.—I went to the Tunnel. The arch being well lighted up, and the whole walk completed, a few visitors were admitted. The coup d’œil was splendid. Mrs. Brunel, Emma, Sophia and her three little children were the first. It gave me great pleasure to see the whole of my family in the new scene.

March 21.—There being no clay above us, there is much to apprehend from the springs. It would be much better to work slower than we do. It is indeed very hard to be under the necessity of driving. Anxiety increasing daily.

No clay above head; should work slower.

Water increasing daily.

March 28.—The top pumps failed; the water rose above the abutting screws. The frames of some of them could not be advanced, nor could the bottom brickwork be laid down—great source of complaint. Isambard called the men in at 10 o’clock; they went on cheerfully. It is surprising that the men are so steady.

Our situation is getting much worse daily.

March 29.—Things are getting worse every day by the influx of water; by which the ground is softened, and the operation rendered extremely complicated and slow. As to the ground, it is evident we are now as Isambard found it by his borings of August last. We have nothing above our heads but clayey silt, and it is of a nature to be detached and run into mud by the action of water.

April 3.—The pumping now requires forty hands. There is no exaggeration in saying that the influx of water, and the badness of the ground, cause an extra expense of 150l. a week.

Obstacles in every way.

April 7.—It may now be said that we are contending with the elements above and around, gaining and disputing every inch that we add to the structure.

April 9.—Isambard’s birthday, he being of age to-day.

April 14.—Doing as well as can be expected from the nature of the ground, and the difficulties that increase upon us.

To be obliged to drive too fast is a sad alternative.

April 18.—The faces are found extremely tender; but having proceeded with great caution, no accident occurred. None, I feel confident, would occur if all idea of piece-work were abandoned. It always operates as a stimulant, a very dangerous one. Obliged to drive on, on account of expense, we run imminent risks indeed for it. That a work of this nature, under such circumstances, should be thus carried on, is truly lamentable. It is obvious that the clay we have above our heads has been broken, by the ground beneath it running or breaking in upon us. We shall have to fight it out until we have a stronger or thicker stratum of clay. Sad prospect indeed it is for us!

April 20.—The ground at No. 1 broke in again, and occasioned great delay. Some bones and china came down.

April 22.—The diving-bell being on the spot, and Isambard having moored it over the shield, he and Gravatt[17] descended at thirty feet water. They found the same substances which had come through the ground into the Tunnel. When Isambard was in the bell, he drove a strong rod into the ground. Nelson, who was in the frame, heard the blows.

A dreadful panic.

April 29.—Ground improving as we advance; we are not, however, free from danger: a dreadful alarm took place this morning. While Isambard and Gravatt were at breakfast, the porter came running in, and exclaiming, ‘It is all over! The Tunnel has fallen in, and one man only has escaped.’ Gravatt was the first to get to the spot, and found all the pumpers upon the floor of the shaft, all stupefied with horror, though every one was there quite safe, and no rush of water was heard. Gravatt and Isambard were soon in the shield, where they observed that a small portion of clay had fallen from the top on the top floor.

May 8.—At half-past three in the morning, an irruption took place, bringing down the deposits of the bottom of the river—lumps of clay, stones, bones, wood, nails, &c., &c., with water. The pumpers and men on the stage (Irish) all ran away, some exclaiming, ‘The Thames is in! The Thames is in!’ Ball and Rogers stood to their post, and soon stopped this most formidable attack.

May 10.—Great difficulties present themselves, that oppose our progress; the chief, however, is the lodgment of water above our heads. There it loosens the silt or sand, and runs out, leaving cavities that cause the clay above to break, and run down in lumps and disturbed streams. This is very awful! This opens the way for the river.

Consequences of want of care more terrific and mischievous than any preceding ones.

May 12.—In moving No. 6, they left by some unaccountable neglect the top staves behind, and in that state two top polings were taken down. The ground being very bad, and high water at the same moment, the ground began swelling. Attention was called to several points, and Gravatt continued in No. 6. He drew out at the front of the top staves a shovel, and also a hammer, that had come through the ground above. They are the same which Isambard left at the bottom of the river, when he went down in the diving-bell.

Triumph of the shield.

May 13.—Notwithstanding every prudence on our part, a disaster may still occur. May it not be when the arch is full of visitors! It is too awful to think of it. I have done my part by recommending to the directors to shut the Tunnel. My solicitude is not lessened for that: I have indeed no rest, and I may say have had none for many weeks. So far the shield has triumphed over immense obstacles, and it will carry the Tunnel through. During the preceding night the whole of the ground over our heads must have been in movement, and that too at high water. The shield must have therefore supported upwards of six hundred tons: it has walked for many weeks with that weight twice a day over its head. What flippancy and inconsistency in some individuals, who, without any knowledge of the subject, without so much as examining the state of the work, will without the least reflection and hesitation obtrude their suggestions upon every case. What shallow conceit for such to pretend they can know better than those that have already the experience that must result from years of deep thought, from days and nights of incessant attention; who have the advantage of the combined talents of several ingenious men, who devote their undivided study, the whole resource of their well-stored minds, to the enterprise; and to add to this, the benefit of the skill of one hundred miners and excavators. Among this class of men, some have been employed in the most perilous enterprises, when each individual must have acted upon his sole judgment, where, in fact, there is no room for an engineer to instruct and direct their efforts. How easy it is to attack everything, to detract from the merits of the best plan. There is always some weak point which may be open to the penetration of the shallowest mind. Then comes the exulting expression, That I always said would never do, &c., and all the consequences with it.

How easy to detract.

May 15.—The water increased very much at 9 o’clock. This is inquiétant! My apprehensions are not groundless. I apprehend nothing, however, as to the safety of the men, but first the visitors, and next a total invasion by the river. We must be prepared for the worst. I have had no rest for many weeks on this apprehension. Should it occur we must make the best of it, by improving our situation.

May 17.—There is no doubt of the ground having improved very materially since last Saturday. Very cheering indeed.

May 18.—Visited by Lady Raffles and a numerous party. Having had an intimation by Mr. Beamish of their intended visit, I waited to receive and to accompany them, not only from the interest I felt at being acquainted with Lady Raffles, but also from motives of solicitude, knowing that she intended to visit the frames. Indeed, my apprehensions were increasing daily. I had given some instructions for enquiring where we could obtain clay, that we should have some barges full of clay to be in readiness. I was most anxiously waiting for the removal of the tier of colliers that was over us, being convinced that we should detect some derangement then. I attended Lady Raffles and party to the frames, most uneasy all the while, as if I had a presentiment, not so much of the approaching catastrophe to the extent it has occurred, but of what might result from the misbehaviour of some of the men, as was the case when the Irish labourers ran away from the pumps and the stage. I left the works at half-past five, leaving everything comparatively well: Mr. Beamish continued on duty.[18]

Mr. Gravatt’s account is as follows: I was above with I. Brunel looking over some prints, Beamish being on duty. Some men came running up and said to Isambard something I did not hear. He immediately ran towards the works, and down the men’s staircase. I ran towards it, but could not get down. I leaped over the fence, and rushed down the visitors’ stairs, and met the men coming up, and a lady, who I think was fainting. Met Flyn on the landing-place, who said it was all over. I pushed on, calling him a coward, and got down as far as the visitors’ barrier. Saw Mr Beamish pulled from it. He came on towards the shaft walking. I went up to him to ask him what was the matter. He said it was no use resisting. The miners were all upon the staircase; Brunel and I called to them to come back. Lane[19] was upon the stairs, and he said it was of no use to call the men back. We stayed some time below on the stairs, looking where the water was coming in most magnificently. We could still see the farthest light in the west arch. The water came upon us so slowly that I walked backwards speaking to Brunel several times. Presently I saw the water pouring in from the east to the west arch through the cross arches. I then ran and got up the stairs with Brunel and Beamish, who were then five or six steps up. It was then we heard a tremendous burst. The cabin had burst, and all the lights went out at once. There was a noise at the staircase, and presently the water carried away the lower flight of stairs. Brunel looked towards the men, who were lining the staircase and galleries of the shaft, gazing at the spectacle, and said, ‘Carry on, carry on, as fast as you can!’ Upon which they ascended pretty fast. I went up to the top and saw the shaft filling. I looked about and saw a man in the water like a rat. He got hold of a bar, but I afterwards saw he was quite spent. I was looking about how to get down, when I saw Brunel descending by a rope to his assistance. I got hold of one of the iron ties, and slid down into the water hand over hand with a small rope, and tried to make it fast round his middle, whilst Brunel was doing the same. Having done it he called out, ‘Haul up.’ The man was hauled up. I swam about to see where to land. The shaft was full of casks. Brunel had been swimming too.

The first alarm, as I heard it, was as follows: Goodwin, in No. 11, said to Roger, in the next box, ‘Roger, come, help me.’ Roger said, ‘I can’t, I have my second poling down, and my face will run in.’ In a little time Goodwin said, ‘You must come,’ which Mr. Beamish directed him to do. Roger turned round and saw Goodwin through a sheet of water. Corps, a bricklayer, went to help Goodwin: he was knocked down. Roger made his way alone, calling to Mr. Beamish, ‘Come away, sir, ‘tis no use to stay.’ Roger saw Corps fairly washed out of his box like a lump of clay.

Sir Isambard’s journal continues:—