Arthur's Pass Tunnel.

Progress, 1 October 1907, Page 451

Arthur's Pass Tunnel.

In connection with the Arthur s Pass tunnel contract it is interesting to learn that , there is at each end approximately 110 chains „ of bank formation, to consist principally of spoil excavated from the tunnel, which is approximately estimated at 320,000 cubic yards. The entrance to the tunnel on the Canterbury side is on the opposite side of the river to the coach road, and enters the hill about a quarter of a mile before the coach road ascends the steep gradients through Arthur's Pass. The tunnel, which will take a straight line through, without curves, will have a gradient of 1 in 33, and at the Otira end will debouch on the south-east bank of the Rolleston river, some 50 chains up-stream from its confluence with the Otira river. The work will be prosecuted from both ends, and the problem of the alignment of the two drives, so that they will meet not only in azimuth, but also as regards levels, depends upon the accuracy of the observations of the engineers. The broken nature and physical conditions of the country practically preclude observations being taken over the hills in the direct line of the tunnel, so that the positions of the tunnel entrances at Otira end and Bealey end, 5J miles distant from each other, have been fixed by triangulation. In tunnels where alignment observation can be taken directly over the longitudinal axis, the question of the meeting of the drives is to a very considerable extent simplified, but in the case in point, where such direct observations are impracticable, the correctness of the alignment must depend upon triangulation. The survey in this connection was carried out by Mr. Hugh Vickerman and Mr. Atkinson, both of the Public Works Department. The method of drilling, whether by compressed air or hydraulic power, will depend upon Mr. Murdoch McLeans investigations in Europe, but in all probability compressed air will be adopted. Mr. Leslie H. Reynolds

* In some experiments in 1906 at King's Norton England the writer recorded consumptions as low ab-2 57°/, of the total steam

estimates that on the Bealey side 1000 h.p., and at the Otira end a minimum of 500 h.p., will be required for the work. This power can be obtained in the first instance from the Punchbowl creek, which has a fall, measured from the level of the tunnel entrance, of some 730 feet, with an estimated minimum supply during winter of some 9 to 10 heads, a head being equal to 1 cubic foot of water per second. On the Otira side, the Otira river, with some 30 heads minimum supply and a fall of 457 feet, can supply much more power than is required, as this river, during heavy flood in the gorge where the head works would be, simply plays with boulders up to 10 and 20 tons weight. It should therefore be at once apparent how difficult a task the engineers have in front of them to put in head works for a supply. Holt's creek, or] the same side of the gorge, with a fall of 74C feet and a minimum flow of some 7 heads will, it is estimated, supply some 500 h.p. ■ but the source of supply, whether Holt's creek or the Rolleston river, will be decided by Mr. Neil McLean and j Mr. Leslie H Reynolds, who purpose making investigations within the next two or three weeks.

We have received the following letter f ron Mr. Arthur Dudley Dobson, city surveyor of Christchurch :— ' In Progress for September you gave an accouni of the Arthur's Pass tunnel in which there were some errors. Mr. Edward Dobson, M. Inst. C.E. late Provmcial-Engmeer of Canterbury, is still verj much alive, and is at present residing m Christ church. Some of the statements in your extrac irom ' Haast's Geology ' are also incorrect, but yoi are in no way responsible for them because I callec Sir Tuhus Yon Haast's attention to them when h< had'the proofs but he forgot to make the necessan corrections. Arthur's Pass was discovered by myself. 1 had < , contract with the Provincial Government to explon W survey the)Fest Coast from the Grey river t< ■Abut Head, and also to survey up every leadinj stream. Having spent some months on the coas surveying with a Maori party, I returned to Christ church by way of the old Maori track at the Hurunu Saddle My Maoris told me there was a pass some times used between the Waimakarin and the Tere makau, and, seeing that that would be a short cut I tried to ascertain if I could get horses through, went up the Bealey (which I named) and, crossmj the Saddle, went down into the Otira. Finding 1 impossible to take my horse through, I returne< into the Waimakarin and crossed northwards int. the Hurunui, and took my horses down the I ere makau to the beach This was before any road were made. Soon afterwards I sent a sketch rlai of the Pass, with the altitudes taken by aneroid, t< Mr Cass, then Chief Surveyor. Shortly afterward the Provincial Government decided to make a roa< to the diggings, which had then been discovered an, they sent my late brother, George, to explore all th passes at the head of the Waimakarin. He exam mcd and reported on all the mam passes, and state* that Arthur's Pass was the only one over which road could be made— hence the name. My fatne subsequently made the road over the Pass. It rather amuses me to notice that every now am then amateur explorers, with the aid of the coac road and the many sheep tracks which have bee cut to let the sheep reach the grass on the mountai top re-discover these cols with a nourish of trumpets suffering many hardships and imagining that they ai in regions which have never before been explored.

Two rivers are to be diverted into the Homestak mine m South Dakota, one of the greatest gol producing mines in the world, which has been o fire for more than two months. There are 100 mik of tunnels m the mine, and it will take at least a fort night to flood them sufficiently to extinguish the fin ****** San Francisco can employ all comers for at leas five years and the population thus added will remai in the State. California has received an impetu thiough the fire that has sent it forward by leaps an bounds, and more people have come to settle on H farms and handle its agricultural possibilities tha ever in any year of its former history It has bee estimated "that, as far as the business district concerned, and excluding the lodging houses hote and residences, the city has been practically on half re-built, and that m another year but little trac of the fire will remain in the business district < bin Francisco