RAILWAY LINK

New Zealand Herald, Volume LXIX, Issue 21327, 31 October 1932, Page 6

RAILWAY LINK

tTARANAKI TO AUCKLAND ENGINEERING TRIUMPHS y/AR EXPERIENCE UTILISED DIFFICULT TRANSPORT PROBLEM No. V. The difficult nature of the task which confronted the engineers in building the Taranaki-Main Trunk railway has placed ''this work among the most spectacular of engineering ti'iumphs in the Dominion. The formidable barrier presented at Tangarakau lias already been dealt with, together with the establishment of the base camp there, from which the completion of the railway was undertaken in earnest. War experience assisted the engineers in overcoming at least one of their problems when a method used by the New Zealand Tunnelling Corps in throwing a bridge across the Canal du Nord during the retreat of the Germans in 1918 was applied to spanning the Tangarakau River. The 80ft. central span of the bridge rests on concrete piers 50ft. above the water. As the river is subject to sudden floods it was impossible to erect any superstructure with any degree* of certainty that it would be allowed to remain in place until the job was complete. Tha 80ft. girder to carry the line was erected on land, and then counter-weighed with a 60ft. girder for the shore span and several tons of ballast. The central span •was then drawn across from rollers by a winch operating from the opposite side of the river, and when it reached its final position it was still in a state of balance. Problem of Transport The launching method was brought back from France by the resident assist-, ant engineer at Tangarakau, Mr. B. C. Annand, who served in the Tunnelling Corps, and was applied for the first time in New Zealand. On the historic occasion it was carried out under the direction of Captain J 7 D. Holmes, while at Tangarakau Mr. R. Lancaster worked out the details, which were approved by the Public Works Department.

Bridges on the final section of the line are not numerous, the o.ily other notable one being, that over the Raekohua Stream, between Tahora and Tangarakau. This bridge crosses the stream immediately the line emerges from tho first tunnel on that three-mile section. The rails are 56ft. above the water and the spans were placed in position by means of an aerial cableway.

The chief problem from an engineering point of view, however, was transport, and from the time the base was established at Tangarakau until the last of the big tunnels was pierced, methods ■were being constantly altered to meet changed conditions. The divides of the Mangatatoko, Mangaone and Mangatete Streams—tributaries of the Tangarakau River which ultimately joins the Wanga-nui-r-each towering 600 ft. to 700 ft. above the floors of the valleys, were the barriers in the railway's path. This necessitated the drilling of four tunnels of 31£, 54£, 63£ and 52 chains in length, an aggregate of over 2j miles, in only twice the length of railway. Day and Night Tunnelling To employ the railway formation and tunnelling as it* could be completed from Tangarakau was out of the question, if only for the reason that so much tunnelling was involved that it would mean many years before the last one could be pierced from a single working front. The job had to be tackled from every conceivable point, and even then it was six years before the last tunnel was holed. During most of this time tunnelling proceeded continuously day and night, with three shifts of eight hours, each of the tunnels being attacked from both ends as soon as they were opened up by the advance parties.,. Transport over and beyond the deep valleys and the four high ridges to these parties was successfully overcome by electric tram, jig-line, hill road, horse tram, corduroy tracks, motor-trucks' and horse and sledge. Huge cuttings and fillings are also a feature, and -the first large filling lies in the Mangatatoko Valley, just beyond the initial tunnel of 31 chains. This valley is crossed by an embankment six chains long and 80ft. high, containing 100,000 cubic yards of spoil. It was built of? a trestle and took three years to complete, the spoil being obtained from a huge cutting beyond. Difficult Hill Roads Had the construction of this filling been delayed until after the completion of the Erst tunnel valuable time would have been lost so, at a cost of £1550, a jig-line 40 chains long was built over the hill with grades as steep as 1 in I£. Transport over this hill cost 10s a ton. The next "problem was to reach tho Mangaone Valley, and for this purpose a hill road of 50 chains, /with 1 in 7 grade, both up and down, was built over a distance of 1J miles. Tractors pulling sledges were first used, but the grade was so bad and the formation so muddy that these were not a .success. The road was corduroyed and transport maintained with 30cwt. trucks, which carried as much as 60 tons a week successfully. The cost, however, mounted to 35s a ton over that ridge. Through the Mangaone Valley a bush tram with horse-drawn trucks was utilised. In 1929, owing to the demand for relief for unemployment and the fact that the number of men on the works was increased to 400, additional formation was necessary to keep them all employed. In consequence formation was advanced over the third ridge through which the tunnel was under construction. Sledge tracks having been cut, a camp was established in the Mangatete Valley, but as insufficient work was offering there, the ada.vance parties were moved over No. 4 ridge by sledge tracks into the Tikapuiti ■Valley, where a canvas camp was established. Provision o! Power So difficult was the country that enormous difficulties wtyre experienced maintaining transport with this camp. Much of the material could not be taken by the sledges, and / had to be manhandled for over'three miles, across two ridges 800 ft. -- above the valleys. The tracks were quagmires all the winter, and working from Tangarakau became so impossible that in 1930 the Tikapuiti Valley was handed over to the eastern side, where more natural access could be obtained. With the penetration of the tunnels the problems of transport were gradually reduced, and the use of the electric locomotives on power lines greatly facilitated tho work. The use of this plant as well as the pneumatic drills at the tunnel faces necessitated tho ejection of many miles of high voltage power lines and piping to carry ..compressed air. The latter had to have boosters in the Mangaone and Mangatete valleys to maintain pressure. Five miles of electric cable were erected, but although there was a serious loss of voltage in the direct current from 500 volts at ' the power-iioose to around 380 to No. 4 tunnel, operations were carried on without the provision of any boosting plants by means of a carefully-organised timetable.

(To be continued)