PROJECTED CHANNEL TUNNEL.

Globe, Volume II, Issue 167, 18 December 1874, Page 3

PROJECTED CHANNEL TUNNEL.

The present Channel tunnel project, which is proceeding under the direction of a committee of promoters, of whom Sir John Hawkshaw and Mr Brunlees are the practical advisers, is, says a contemporary, a simple, intelligible one, and has been considered with much care and an effective amount of investigation. The grey chalk—a mass of strata 500 feet thick and impervious to water—which forms the principal mass of the cliff at both Dover and Calais, strikes across the channel with so little divergence from the horizontal that a tunnel could be pierced within the vertical bounds of its thickness. To ascertain exactly the configuration of its outcrop, and the surface outlines of the other associated cretaceous rocks—the white chalk above it and the gault and greensand below it—numerous soundings and borings of the sea-bed have been made in a most ingenious manner by means of an iron tube, over which a hollow shot, fitting loosely, is raised and let fall upon a flange attached to the tube, the end of which is in this way driven into the substance of the sea bottom, the core thus obtained giving the required sample of the rock perforated. Some hundreds of these borings have been made, and a complete geological chart of the Channel constructed from these data. These accurate details of the strata and their out-crops have enabled the most promising line of route to be selected, and which is accidentally very nearly that of the Dover and Calais submarine telegraph cable. The plan and construction of the proposed tunnel has the joint approval also of M. Durioch, M. Bergeron, M. Lavellee, and other associated engineers of eminence, and may thus be described. The line of the main tunnel, which is to be large enough for a double line of railway, is drawn straight from St Margaret's Bay, South Foreland, to a point very nearly midway between Calais and Sandgate. On the English side the London, Chatham, and Dover Railway will run off between the suburb Carlton, and the town of Dover, whilst the South Eastern Railway will branch off from about Shakspeare Cliff, aDd passing to the rear of the Heights, will cross t/he harbor line of the former company, and join the line to St Margaret's. Thia being parallel with the shore makes a sharp turn near that village, the alteration of the direcrion being there approximately aright angle. On the French side the connecting line bends diagonally to the westward, and joins in a fork the Boulogne and Calais Railway. In the longitudinal section the proposed tunnel presents a Blight fall of 1 in 2010 from the nentre towards either extremity, and the vertical depth of the. highest point of. iti

floor is 436 feet from Trinity high-water mark, and 200 feet beneath the sea bottom itself. From the land levels of the existing railways the two approaches make long descents of over four miles each with gradients of 1 in 80 into the tunnel ends, over two miles being under the sea, the total of the whole amount of tunnelling amounting to thirty miles. The geological section given by the engineers is made to shew white or upper chalk above the grey chalk, unbroken and horizontal for the whole distance, and the tunnel boring rather above the median line of the grey chalk beds. The greatest depth of water over the sea bed above the tunnel is stated to be 180 feet. Below therailway approaches, and continuous with the floor of the submarine t'innel itself, there will be at each end a driftway leading to vertical shafts ashore for drainage and ventilation. These terminal shafts and shiftings are the preliminary works which it is intended to make as tests for the practicability of the general undertaking, and of which, when completed, they will form essential portions. The drawings and specifications for them have been duly prepared, but the tenders will not be let until the financial arrangements are completed. The shaft will be 19 feet in diameter, built round with 24 inches of brick laid in cement, and the headings, which will be driven by machinery probably Brunton's— will be lined with 14 inches of brickwork, and have internal diameters of seven feet. Their form

&®1 be horseshoe, w ith straight sides, and a 9&fc inverted arch below the floor. The estimate for the entire preliminary works—which, to satisfy the amtur propre of both nations, will be carried on simultaneously in both countries —is, with all expenses contingent on their execution, Fomething less than £160,000, including the two pumping engines of 2,000,000 horse power each. The total cost of the whole tunnel and its accessories is, for the present, put at £10,000,000; but there are those among the engineers who think the preliminary works will afford data for a much lower estimate. The Channel tunnel project is to be carried out by a French and an English company, the general management to be vested in a committee whose numbers will be furnished by two directorates. Towards the preliminary engineering works each company is to contribute £BO,OOO, of which £40,000 is definitely promised by the Northern of France ; and £20,000 more is added by Rothschild Brothers of Paris, whose intimate relations with that railway arc well known. The residue will be contributed by the Blench members of the promoting committee. With the English company no advance has been made over the original £30,000 subscribed in 1872 ; but its moiety of the preliminary total, it is expected, will also be subscribed privately. The actual position of affairs at this time is that the projet dc loi has been prepared, and will be presented on the reassembling of the French Chamber in November by M. Cailaux, now Minister of Public Works, and formerly a member of the Channel Tunnel Committee—the aspect of this Channel Tunnel scheme having thus changed from adverse under the Government of M. Thiers to conditions not unfavorable under that;of Marshal MacMahon. Nothing further can be done until then to advance matters beyond their present position, and of course nothing more substantial is likely ever to be effected until a concession be obtained, for no body of capitalists could pledge themselves to or would proceed with actual engineering operations until lawful security for their expenditure and rights of monopoly were actually acquired.