But I should be sorry to enter with any such determined feeling into a discussion of the merits of the particular mode of construction. I would refer to my last Report for the reasons which influenced me, and the objects I had in view in introducing the piling; that part which had been made under my own eye answered fully all my expectations. Here the piles did answer their purpose, and no inconvenience resulted from their use. The difficulties which we have since encountered, the bad state in which the line was for a considerable time, and which is only recently improved, have undoubtedly been aggravated, if not caused, by these piles; but not, as I believe, from a defect in the principle as applied in our case, where the line is mostly in cutting, or on the surface, but from defective execution; for, notwithstanding the determination to allow sufficient time for this most important operation, yet, to make up for previous delays and loss of time, it became necessary at last to force forward the work more rapidly than was at all consistent with due care in the execution; and during the whole of this period I was most unfortunately prevented by a serious accident from even seeing the work almost until the day of opening, when I ought to have personally superintended the whole. I do not mean that the work was neglected by those whose duty it was to supply my place—far from it; but in such a case, a new work cannot be properly directed except under the eye of the master. Following exactly the plan which had succeeded on the first piece completed, several serious faults were committed. A much greater density and firmness of packing is required than was previously supposed; the mode of packing adopted, and the material selected, in the first instance, have proved defective elsewhere; and over a great extent in the line, particularly in the clay cuttings, and where the work was at last most hurried, it has been badly executed. But many parts have stood well from the commencement; others are fast improving; and I have the satisfaction, although a very painful one, of seeing that if, in the first instance, a foundation of coarse gravel had been everywhere well rammed in before the timbers had been laid, and the packing formed upon this, we should, from the outset, have obtained as solid a road as we have now over a great part of the line. What we have been able to effect since the opening of the line has necessarily been a slow, expensive, and laborious operation. We have been compelled to open the ground, and excavate it to a depth of 18 inches under the longitudinal timbers, and this without interrupting the traffic: to remove the whole of the material thus obtained from off the line, and to replace it by coarse ballast; and not having the means of sufficiently consolidating this ballast by ramming while the timber is in its place, the packing has to be repeated once or twice after it has been compressed by the passing of the trains. This new packing, however, does stand, and in a few weeks I expect the line will be in a very different state from that in which it has been, or indeed now is. From what I have described as the result which can now be, and might have been, obtained from the commencement, it will be inferred that I am disposed still to defend the system of piling. I certainly could not abandon it from conviction of its inefficiency, for I see proofs of the contrary; and I feel that under similar circumstances I could now prevent the mischief which has occurred. Upon that portion of the line where the permanent way must next be formed, piling could not be resorted to, the ground being a solid hard chalk for many miles. I had intended, however, recommending the same principle, but in a different form, holding down the longitudinals by small iron rods driven into the chalk; but the same objection could not exist, because the chalk cannot yield under the timbers like clay, or even gravel. But I should wish most anxiously to avoid anything like an obstinate adherence to a plan, if the object which I believe essential can be obtained by other means, particularly when, that plan being my own, I may be somewhat prejudiced in its favour. I find that the system of piling involves considerable expenses in the first construction, and requires perhaps too great a perfection in the whole work, and that if the whole or a part of this cost were expended in increased scantling of timber and weight of metal, that a very solid continuous rail would be formed.
For this as a principle, as for the width of gauge, I am prepared to contend, and to stand or fall by it, believing it to be a most essential improvement, where high speeds are to be obtained. I strongly urge upon you not to hesitate upon these two main points, which, combined with what may be termed the natural advantages of the line, will eventually secure to you a superiority which, under other circumstances, cannot be obtained.
As regards the expense of forming the permanent way on this principle, I am quite prepared to maintain what I have on a former occasion advanced: that even on the system which we have adopted between London and Maidenhead, the total cost does not materially exceed that of a well-constructed line with stone blocks. I did not make in the outset an exact estimate of the cost of either mode; I was unable to obtain the cost which has actually been incurred on other lines; but a comparative estimate was made, and the result of that comparison led me to state that the one might exceed the other by 500l. a mile. The actual cost of our permanent way appears, by the detailed account which has been made out, to have been above 9,000l., including expenses of under-draining and forming the surfaces which cannot be included in the cost given in other cases, because that drainage (although I believe generally forming part of the plan) is not yet constructed. This sum includes the sidings at the stations, switches, joints, and other contingencies, and also the expenses incurred during the first month of working the line, and which, as I have before stated, consisted in removing and replacing work which had been improperly executed. These items will make a considerable reduction; and besides these, larger reductions may be effected in parts of the work which were new, and, from the circumstances naturally attending a first attempt, were not so economically conducted as they might be, or indeed, as they were towards the close of the works, when the different parts were let by contract. Taking the prices at which the work was latterly actually executed, 8,000l. per mile would be a liberal allowance for our future proceeding, even adopting the same system; and with a modified system, such as that suggested of simple longitudinal bearers of large scantling, and a rail of fifty-four pounds per yard, at the present high price of iron, the cost, calculated upon our actual past expenditure, would not exceed 7,400l. per mile. This, I am aware, is a larger sum than that which has usually been assumed as the cost of the permanent way. I cannot prove that others have cost more, or even so much as this, as I have nothing but the published accounts to refer to; but this I can state, and prove if necessary, that rails and blocks, such as are now being adopted on the Manchester and Liverpool Railway, would upon our line cost at least as much.
The prime cost of rails and chairs delivered on the line would alone amount to half the money; and nothing is, perhaps, more certain than that the experience of other lines within the last two or three years has proved that this part of the construction of a railway is unavoidably much more expensive than was ever calculated for at the time our estimates were made.
I am, gentlemen, your obedient servant,
(Signed) I. K. BRUNEL.
APPENDIX II.
(See Chapter IX. on the ‘Great Britain’ Steam-Ship, p. 254.)
Report to the Directors of the Great Western Steam-Ship Company.
October 1840.
GENTLEMEN,—I have now the pleasure to lay before you the result of the different experiments which I have made, and of the best consideration I have been enabled to give to the subject of the screw propeller.
The observations which I have to make are naturally divided under two principal heads, namely: first, the simple question of the applicability and efficiency of the screw considered merely as a means of propelling a vessel, compared with the ordinary paddlewheel; and, secondly, the general advantages or disadvantages attending its use.