FEATURES OF THE SCHEME

Evening Post, Volume CIV, Issue 10, 12 July 1922, Page 5

FEATURES OF THE SCHEME

Renewed interest is now being taken iin the Channel Tunnel project. This was much in evidence a few weeks ago, when the French Channel Tunnel Committee, headed by M. Paul Cambon, its president, was entertained at the House of Commons by Sir Arthur Fell and the members of the British Committee. M. Paul Cambon then clearly expressed the desire of Frenchmen for the construction of the tunnel, not only because of all the economic advantages which they realised it would confer, but, because also they saw in it a valuable means of drawing the two nations closer together. Such a union of the two peoples was regarded as the best guarantee of peace in Europe, and France was anxious to bring it about, because she was profoundly pacific. In face of all the vicissitudes of European politics, says the engineering correspondent of the Daily Telegraph, the supporters of the Channel Tunnel on both sides of the ."silver streak" have been the champions and the most steadfast upholders of the Entente Cordiole. After forty years of patient waiting a number of the original propounders of the scheme are even more enthusiastic and confident that they will yet see the realisation of their hopes. The time which has elapsed since the original works were carried out and then shut down in the early 'eighties has not been wasted. Engineering progress has served to minimise whatever engineering difficulties may then have existed. TWIN TUNNELS PLANNED. At this time, therefore, a brief recapitulation of the salient features Of the scheme seems to be justified. The practicability of the project has long been agreed upon by engineers on both sides of the Channel. Two tunnels, each 18ft net diameter, are to run side by side at a position some 150 ft below the bed of the straits. The tunnel, would be 36ft apart, measuring from centre to centre. At convenient intervals they would be connected together so that in addition to convenience in construction, if either tunnel were in part or wholly blocked by slight mishap less inconvenience would be experienced through the other tunnel being available at longer intervals of time, for traffic in both directions. Many advantages accrue to the use of twd single-track tunnels in preference to one double-track tunnel. In addition to the greater strength of the smaller diameter, there is also the advantage of the easier' accommodation of the smaller height in the available depth of the stratum through jvhich the tunnel will be pierced. Experience has shown that the tunnels will need to be lined. Cast iron segments with grouting outside will sup-.j ply needful strength against pressure above and impermeability to water respectively. The tunnels will carry the | largest rolling stock of both British and Continental railways with the exception of steam locomotives, which will not need to pass through, powerful electric locomotives supplying the tractive effort in the tunnel. The tunnel will be brilliantly lit throughout, and everything done which- can be done to secure the comfort and safety of passengers. The time involved iri the passage through will be about forty-five minutes, and any small experiences of the loss of time occasioned by the present unavoidable delays at the ports gives some conception of the savings which could be effected by the long tube. The first stage in the work involves cutting a 10ft diameter drainage tunnel from both sides and slightly inclined up to the middle of the Channel. This would occupy a considerable proportion of the time; but would subsequently enable the work on the main tunnels to be considerably facilitated. Electrical power would rule in all the operations of borj ing, and a rate of progress never be- ' fore attained should be easily possible. Ultimately the tunnel would be worked from a power station in Kent, possibly ten miles inland, and all fears of misuse can very simply be' safeguarded by the insertion of bends at either end, which could in extreme emergency be flooded, effectively cutting off communicaj tions without the least damage to the tunnel or to the associated works.. A scheme of this character, however, raises many matters of interest and importance. i VENTILATION NECESSARY. Thus the matter of ventilation is one of supreme importance. Efficient ventilation will necessitate very large volumes of air, but by no means so large as would be required if steam propulsion were adopted. Helpful guidance is not wanting in tMs matter. It is. estimated that a volume of 100,000 cubic feet per minute would suffice to effect efficient ventilation, and this amount gives no occasion for anxiety to engineers. The Simptan tunnel has provided some experience in tunnel ventilation. Though the tunnel is less than half the length of the proposed channel submarine-way, yet it is situated at a depth of some 7000 ft below the surface, and according to- all usual experience a very perceptible temperature should, and, indeed,' did, occur there. In this case again steam locomotion is employed to and from the tunnel, while electricity is used in the tunnel. Yet at this greatest depth to which man has ever been, there is no difficulty in maintaining an adequate supply of air, cool and fresh. Again, the tunnel under the Mersey at Liverpool is thi-ee-q__rters of a mile long, and has 100 ft. of wateir above it. When, in its early- days steam traction was employed, no - less than 600,000 cubic feet of air was required per minute. When, later, electric locomo-tion.-was adopted in the tunnel, the air supply could be reduced to one-fifth of this amount.

Another point which arises in ventilation is the direction in which the. air would be admitted in each of the tubes. With long tunnels worked by steam the most satisfactory method is that of "blowing the air against the moving train. Driver, fireman, and passengers are thus moving continually into fresh air, leaving the products of more or less complete combustion behind them. These then should have sufficient time to diffuse down to quite comfortable proportions before meeting a following train. With electrio locomotion the air would travel in the direction of the train, and its motion thus be helped by it. It has been estimated that when a full complement of trains pass through the tunnel—that is, something of tho order of one each way every ton minutes—the yolume of air required would bo about 45,000 cubic feot per minute in each tube, a volume whkh could bo negotiate, with sas.. Tftg problem awjr he »*g*r_*d:« oJLww*

parative simplicity, especially when the difficulty and concomitant urgenoy of keeping the air of coalmines pure and fresti m order to ensure safety is remembered, and_ also the success which is already achieved. FIRM STRATUM OF CHALK AND | CLAY. ' Upon the aetaal depth and course of t the tunnel there has doubtless been occasion for varying _ opinions. _ A large amount of geological exploration is not ! only required, but has already been carried out, much of it quite a long time ago. _!y means of a machine specially designed, Sir John Hawkshaw took no fewer than 7000 samples from the bed of the Channel, by means of which a detailed exploration of the bed became possible. What obviously is wanted is the placing of the tunnel in a stratum which should be strong- a_d impemneable, one in which there would be very little fear of infiltration of seaw-ater. Such a material appears to be there—and in an ideal position too. In the continuous lower chalk there is a bed which consist* of ch_lk marl. This contains 80 .per cent, of carbonate of lime and 20 per cent, of clay. This clay gives impermeability to water. The stratum is, moreover, very suitably placed in the narroweat portion of the Straits of Dover, and while ii would not take the shortest possible straight-line tunnel, the deviations i herefrom are by no means considerable, and the tunnel would start from Shakespeare Cliff on the Dover side to Sangatte on the French coast, and would thus follow much the same course as that now taken by the steamers. Indeed, Mr. H. C. Tempest, general man- j ager of the South-Eastern and Chatham Railway and chief engineer to the Channel Tunnel Company, regards any attempt outside this stratum as a. foolish venture. The grey marl has stood the test of time, for the tunnel bore on the English side, which was cut as long ago as 1881, and which extends under the sea to a distance of one mile and aquarter, was attended by the inlet of no more water than could be easily dealt with with a small hand pump.

Nevertheless, there will always be the possibility of meeting water, and of its . presence ample warning can be given by devices on the piercing-head. That even very large inlets of water could be dealt with may fairly be assumed from the experiences of previous work. Something at least was learned frtfm the very serious inrushes of water which occurred in connection with the Severn Tunnel. At one time no less than 24,000,000 gallons were pumped <n»t per day, and on one occasion the progress of the work was stopped for twelve months. Much more recently the case of the Mont dOr Tunnel gave a striking demonstration of success against big odds, for between Frasne and Yallorbe an inflow of no less than 96,000,000 gallons per day was met and successfully surmounted. Moreover, there have been many-cases in which successful bores through waterlogged strata have been made, and there is thus no great reason to fear that the ingenuity and accumulated experience of the engineer will not be equal to all the difficulties which may be confronted. DISPOSAL OF EXCAVATION. A very simple calculation will _wv« to show that considerable quantities of excavated material will have to be dealt with. There is first the journey to the coast, and then the disposal. For a work of this magnitude, new and possibly novel methods of handling—or rather not handling—may be called into requisition. Therein lias one of the constructional functions of- the drainage tunnel. This must' of necessity be cut from the two ends only. Originally it had been proposed to construct a double narrow gauge line in each of the larger tunnels, so that the excavated material could be transferred to trucks by endless conveying bands brought right up to the working face. It is of the utmost importance that all operations should be effected with the maximum speed. Considerations of interest on capital1 necessitate this, and the saving of even a few months on the period of cutting the tunnels will be all to the good. When this drainage tunnel has been cut it will permit of the cutting of the main tunnels at a number of points in addition to the ends. Thus a start can be also made in the middle, and at pointsituated, say, equi-distant between the middle and the ends. This arrangement would permit of- eight working faces which would be -in simultaneous operation, effecting a considerable economy of time. Efficiency of the excavating machines is another important point, and the long delay in making a start is being utilised in the perfection of a type of cutting machine designed especially for the material which has to be cut.

The removal of excavated material has attracted considerable attention. Even the use of conveying belts to an almost endless succession of trucks is a system upon which it is not difficult to visualise improvements. An alternative method which has been proposed is that of pulverisation of the comparatively soft chalk and sucking it out by means of air. But a much more promising method is that of the slurrification of the material, and subsequent pumping. This is a system which appears to offer the most promising results, and it' may in time be found'that the delay on the recommencement of the work will be turned to good account in the introduction of methods quite outside the range of the vision of the pioneers of forty- and more years ago. OTHER WORKS. But the cutting of the tunnels will not complete the ideals which have for some time been held by our railway engineers. A vastly increased volume of Continental traffio is anticipated by the companies which now handle the seaborne traffic. The bulk of this will come from London, though it will then be possible to take a through train, say, from Aberdeen to Paris or other Continental centres. An increase in the traffic from the metropolis will _ necessitate terminal arrangements I far in excess of those at present available. An hourly electric service from London to Paris may need more accommodation than that which can be offered by the present Charing Cross, and doubtless interest will once again be evincein the suggestion of removing the SouthEastern and Chatham -terminus to a capacious site south of tho river, possibly alongside Waterloo, leaving room for a little attempt at town-planning on the present Oharing Cross site. This is but one of the proposals made as an adjunct to the Channel Tunnel scheme. Pioneering enthusiasm is still sufficiently alert to prees all the advantages of the tunnel as a weapon of peace and prog»esa, and in the recent words of Sir Arthur Fell, it is claimed that "there is no single work which offers such promising results.as this enterprise, but far above all, France, Italy, England; and Belgium will, combined, give that feeling of security against attack which this tunnel can alone assure. It will be the link ever binding them more closely together, and the outward symbol of thi deep friendship of France and Great Britain—a. friendship which no temporary troubles can affect, and which will assure for both countries a future worthy of their glorious past."