Part 3 (1/2)
_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 s.h.i.+eld we have pa.s.sed close under a body of collected water a few inches only above the staves.
Isambard is too unwell to stay long in the works.
[Sidenote: 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.
[Sidenote: 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 s.h.i.+eld and the superinc.u.mbent 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 circ.u.mstanced! 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 circ.u.mstance, and the apprehension of the water breaking in, are matters of the most dreadful anxiety.
[Sidenote: Superinc.u.mbent weight varying daily, and still more every fortnight. What stress on the frames. The shoes have never yielded; a most important circ.u.mstance.]
_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 s.h.i.+eld 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 s.h.i.+eld. 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 s.h.i.+eld 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 subst.i.tuted. Some have fancied that the ground did not bear wholly upon the s.h.i.+eld 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 s.h.i.+eld 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.
[Sidenote: 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 b.u.t.ting 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 superinc.u.mbent 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 s.h.i.+eld 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?
[Sidenote: 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 astonis.h.i.+ng how the silt resists the sliding of the top staves. a.s.sured 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!
[Sidenote: 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'il 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.
[Sidenote: No clay above head; should work slower.]
[Sidenote: Water increasing daily.]