On the geological conditions affecting the construction of a tunnel between England and France / by Joseph Prestwich ; with an abstract of the discussion upon the paper ; edited by James Forrest.
- Joseph Prestwich
- Date:
- 1874
Licence: Public Domain Mark
Credit: On the geological conditions affecting the construction of a tunnel between England and France / by Joseph Prestwich ; with an abstract of the discussion upon the paper ; edited by James Forrest. Source: Wellcome Collection.
Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.
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![])orings of great depth on the Freiidi coast. Then arose the ques- tion whether the Chalk was continnons. There wore suggestions as to the existence of a great fault. It was thought by some per- sons that the Channel might have been formed by the strata being riven asunder, and that the Chalk might not be continuous. In order to obtain information on the subject they had a steamer in the Channel for several months under the charge of Mr. Henry Brunei, who, with an apparatus contrived for.the purpose, examined the bottom of the Channel for a considerable breadth all across and in the line that the tunnel would probably take. These investi- gations showed, as far as such investigations could show, that the Chalk was continuous; and they afforded remarkable proofs of the accuracy of Mr. Day’s observations, for the outcrop at the bottom of the Channel was found very nearly to coincide with that which he had predicted from his geological inquiries. Having ascertained the outcrop of the strata and the dip, his endeavour was to place the tunnel so that it would run, except at the sides, uniformly through the Grey Chalk, and the question now was whether that was the proper place to put it. There was an observation which he had made over and over again, viz.: that at a sufficient depth it was of no more consequence having the sea above the tunnel than having a mountain above it. But then there w^ere other consider- ations involved in the question. In going down a thousand feet deep it would be necessary to begin a long way off to get to such a depth, and the tunnel would be very long. Unless the tunnel could be so laid out as to pass at a moderate depth under the bed of the Channel, it would be no use proposing it at all. The tunnel proposed by himself and Mr. Brunlees would be about 23 miles in length, and would be nowhere less than 200 feet below the bottom of the Channel. It could be approached from Dover by a gradient of 1 in 80, and it would emerge on the French coast b}’- a similar gradient, so that it could be connected with the railways going to Calais, Boulogne, and Paris. So far, therefore, it was in an engineering point of view in the right situation. With regard to the question of water, he might be permitted to say that land springs, which seemed so serious to the geologists, would not deter an engineer from making a tunnel through chalk. He was now completing, at Brighton, a tunnel 5^ miles in length, wholly through the Upper Chalk, and below the level, and within a short distance of the sea. There was a large amount of water from land springs. The quantity of water pumped in constructing this tunnel varied from 8,600 to 10,000 gallons a minute. This was a large quantity, but it did not prevent the tunnel from proceeding,](https://iiif.wellcomecollection.org/image/b2244614x_0058.jp2/full/800%2C/0/default.jpg)
