[8] The results obtained by these borings were no doubt fallacious, but not to the extent which has sometimes been imagined. At a meeting of the Institution of Civil Engineers, in November 1849, Dean Buckland called attention to ‘the evils arising from the ignorance of the engineers who reported to Sir Isambard Brunel, previous to the commencement of the Thames Tunnel, that the whole of the bottom of the river at that spot was London clay.’ Whereupon Mr. Brunel rose and said, that he ‘agreed that knowledge of every kind was most desirable, and that it would be well if engineers were generally much better informed on many subjects which would be useful, and more particularly on matters connected with geology; at the same time he could not admit that they were deficient in that knowledge of the surface of the earth which was necessary for the purpose of guiding them in their work. It might be true that many members of the profession were, like himself, not perfectly well acquainted with the minute geological characteristics of the soils they had to deal with, but he thought the education and the practical experience of the profession generally rendered them well acquainted with those features and characteristics which were necessary for their guidance in the design or execution of work. He must also say a few words in defence of those persons (now nearly all dead) who made the borings in the Thames, and were stated to have made so fallacious a report previous to the commencement of the Tunnel. Now, although that statement had by constant repetition become a sort of historical fact, it was really only one of those popular fallacies which obtained too ready credence in the world. The position of the Tunnel was not determined by any report, or by the result of any borings, but with a view to establishing a communication between particular localities for encouraging the traffic which was anticipated from the facility of access to the docks, and for other local reasons, such as the general direction of the roads and streets on both shores. After the position was settled, and not until then, borings were made to ascertain what soils might be expected in that part of the river. It must be remembered that these borings were made full twenty-five years ago, when boring in the bed of a river through a depth of water of nearly thirty feet was not an ordinary occurrence. The tool then generally employed was the worm, and tubes were not even used in such cases. The borings showed the existence in that spot of something which, in the ordinary acceptation of the term, might have been inadvertently called London clay, but he had no recollection of its geological designation having ever been thought of. It was reported and shown to be a very fair clay for working in.... The errors which were made in giving the results of the borings did not, in fact, arise from ignorance, but from mechanical defects in the tools, for it was subsequently discovered that the worm frequently carried a portion of the upper tenacious clay through the softer strata beneath, and brought it up again. The tenacious clay might have been called London clay, but no value was attached to that particular designation; they cared little in engineering for its denomination, provided it was of a good tenacious quality. This mistake in terms (supposing it to have occurred) could not have had any influence on after proceedings; for, before the Tunnel was far advanced, he conducted with great care a series of borings extending across the Thames, and, as he used improved tools and worked through tubes, the holes were kept so dry that a candle was frequently lowered down to the bottom in order to see the amount of infiltration. By this means he was enabled to construct a correct section of the bed of the Thames at that spot, showing every layer of shells and gravel as well as every variation of the surface of the silt, &c. He entered more at length into these details than might perhaps appear necessary, because he felt it was incumbent upon those who had the conduct of works to show that they did not proceed so ignorantly or so recklessly as had been assumed, in the design or execution of large undertakings.’
[9] The paragraphs in small type, without any reference, are from Sir Isambard’s journals. The sentences inserted at the side are his marginal summary. Occasionally a few words are added (in square brackets) by way of explanation.
[10] The shaft subsequently made on the Wapping shore was sunk to its full depth without any under-pinning.
[11] Professor Rankine, in his work on Civil Engineering, p. 599, describes the Thames Tunnel works under the significant heading ‘Tunnelling in Mud.’
[12] Proceedings Inst. C. E. i. 34. The circumstances which led Sir Isambard to conceive the idea of a shield, and the earlier designs he made for it, are described, with illustrations, by Mr. Law, pp. 7-10.
[13] Mr. Law’s memoir contains a detailed description of every part of the shield, illustrated by careful drawings.
[14] Mr. Beamish had joined the works on August 7.
[15] On November 20 Mr. Brunel mentions in his diary that he had ‘passed seven days out of the last ten in the Tunnel. For nine days on an average 20⅓ hours per day in the Tunnel and 3⅔ to sleep.’
[16] On the previous day Mr. Brunel had been formally appointed resident engineer.
[17] Mr. Gravatt had been appointed an assistant engineer six months before.