NEARING THE END.

Press, Volume LXV, Issue 19544, 14 February 1929, Page 17

NEARING THE END.

POSITION IN 1566.

ENGINEERING DIFFICULTIES. By . VO rk on the Lyttelton Tunnel had been in progress for four year*. The hill ha J not been pierced, but determination and engineering skill had made good progress possible, so that success was achieved in May, 156..

At this stage, Mr Edward Dobson was sanguine of success and on November Oth, he touched upon some of the more interesting engineering features of the work in an address before tho Philosophical Institute of Canterbury. Mr Dobson was vice-president of the Institute, and he made the following comment during the course of observations on "The Present State of Applied Science it. the Canterbury Province'':—

"Ou the Lyttelton and Christchurch railway, which has been open for traffic between Christchurch and the Heatheote wharf since December 1&63, the works of the Moortaouse Tunnel havo made steady progress, only about 240 yards remaining to be driven at the present time, out of a total length of 2838 vards.

"Independently of the interest attached to these tunnel works, from a geological point of view, as affording a complete section through the side of an extinct volcano, they are of importance as an example of engineering difficulties, gucce&sfully overcome. Drainage and Ventilation.

"The syphon employed for the drain- J age of the upper half of the tunnel j is probably the largest of which there f is any record in the history of tunnel i works, bring upwards of half a mile ' in length, whilst the system of tentila- 1 tion employed, thftt of conducting the j smok<? and foul air through a flue formed by a horizontal brattice, into an j upcast shaft near the tunnel mouth, has j proved perfectly effective. It >• worth remarking that the engineer® of the Mt. i Cenis Tunnel have at last found it ( necessary to employ a similar means of ventilation, the supply of fresh air forced Into the face of the work being insufficient to drive out the smoke which filled tho tunnel like a series of walls of dense fog. j "It may be laid down as a leading axiom, with regard to the ventilation of drives mined with gunpowder, that although fresh air may be driven in by machinery, so as to produce a healthy atmosphere for tho miners, the smoke from the shots cannot be driven out, j but must be drawn oat by creating a vacuum in the direction in which the smoke is to be drawn. The attempt to force smoke, by an air current in the rear, produces generally a dense fog,, in which candles are of little use. [ I A Phenomenon. f "A very curious fact connected with (the bratticing of the Lyttelton Tunnel j may be hare mentioned. The brattice is formed with boards laid on juiirtß, running across the width of the tunnel, and housed at each end into the solid rock. Both joist* and boards rapidly became eovered with fungus and require to be replaced from time to time with new material. Although, after j the first year, portions of the brattice rapidly fell from decay, these falls in- J variably happened on Sunday, when the j men were absent from work, bo fail having taken place while the men were ! at work, until quite recently, when j the decay of the timber bad rendered j necessary an extensive renewal of the i brattice. The explanation of this! curious fact is probably the difference ' of temperature on week daya and Sun days; tho furnace fire at the foot of the upcast shaft being allowed to go ; out on Saturday night f.nd not being > lighted again for 24 hoars; the hot smoke, which occupied the floe daring j the working days, being replaced on j Sunday by a comparatively cool atmo-. sphere. | Example from Franc*. , "I may here mention, that a tunnel] is now being driven in France, on the j new line of railway, between Lyons j and Boanne, under Mount Sarvage, j which divides the valleys of the Rhone and the Loire. This tunnel will be two | miles in length and will be driven from five shafts, of which the deepest will be upward* of 000 feet in depth. From J the geological character of the district, j it is anticipated that the rock to be j bored through will be of the hardest j description, and it is stated in gcien- I tific journals that in one of the shafts the difficulties met with are such that a progress of two inches in twenty - four hours is nil that can be accomplished. "It will be interesting to watch the progress of this work, especially in reference to how far boring machinery can be introduced with advantage in j tunnelling through rocks of equal hardness with those met with in the Lyttelton tunnel. Ends Meet. ! "Some curiosity has been expressed as to the correctness of the alignment of the two ends of the Lyttelton tunnel, and the method employed for checking any error that might be committed is the direction of the work. "The system employed is very simple. A permanent mark is fixed in the centre line of the tunnel, on a tower built on the dividing range, nearly midway between the two ends. A transit instrument being placed on the meridian of the tunnel, in a position to command a view into the tannel, as well as of the tower on the

| hill, it car. he teen at once whether the {flame of a candle placed on the central (line of the work, inside the tunnel, is jin a vertical plane with the mark on (the lower. But it is also desirable, in .case ©f error, to hare the means, not only of correcting, but of calculating the amount of such error, and this can readily be done. The permanent mark on the central tower consist* of a batten *i* inches wide, with a black stripe, one inch wide, down it* centre. jThe eye piece of the transit in#trunsent, , being furnished with five vertical wirt». placed at equal distance# apart, the value oftk* space between any two wires, at a distance equal to that of the mark on the tower, can be ascertained by reference to the width of the b*ti ten, which thus gives a scale by which I the error in the position of a light, t placed in the tunnel under the tower, | can'be rated with great exactness. I "Although it is not probable that any important extension of oar railway can be undertaken at present, it is satisfactory to know that the surveys of the Southern Railway ksve been carried down to the Waitaki and connected with thoae made by the Bailway Engineer of the Otago Province, and that the neeeaaarr reserve* have been msde, so far as the lines run through land belonging to Ike Govern - | meat." ' Whet: the two ends met oa May 24th, 11M7. the alignment was found to be J within a few inches of the correct position, and when finished, the tuaael Was found to be tSTO yards long, 31 yards I longer than estimated.