ENGINEERING DIFFICULTY

Waipa Post, Volume 36, Issue 2147, 21 April 1928, Page 7

ENGINEERING DIFFICULTY

FACTORS IN RAILWAY BUILDING. An interesting history of the construction of the Taranaki-Main Trunk railway onwards from the present railhead at Tahora was given by Mr B. C. Annand, A.E., to a party of New Zealand civil engineers who paid a visit of inspection to the works recently. Some of the roughest country through which a railway is being constructed in New Zealand at the present time is to be found about 50 miles north-east of Stratford, said Mr Annand. Here 25 miles, remain to he linked up between Tahora and Ohura to complete the line between the Main Trunk railway at Okahukura and Stratford. The portion being constructed from the west end is a distance of 9i miles comprised of two sections, Raekohua 31 miles and Heao 61 miles. On mapping out the programme of work it was decided to concentrate on the Heao section, thus enabling both sections to be completed at the same time.

The main difficulty which presented itself on the Heao section was the transport of material. For a distance of 61 miles the surveyed line ran through virgin bush country, crossing several leading spurs until it landded out in the Heao Valley, a valley which had been settled for many years and which leads off from the Ohura Road near Tatu. It is because of these high ridges that the 21 miles of tunnel on this section were necessary. Ordinary roading was out of the question as these ridges rose about 800 feet above the streams and the transport of material was done with jig lines, tramlines and steep roadways.

Power was needed for this heavy transport and it was decided to erect a power-house to supply power oyer the section. Owing to a large quantity of electrical equipment being available from Otira, a D.C. generator had to be installed, and is driven by plant transferred from Mangahao. Where possible, mechanical means have been installed, resulting in efficient work and steady progress. The surveys for this line from Tahora on to the Heao Valley were made some years ago, but relocations have since been made, making improvements in alignment and lessening costs. At the present time a party is completing the final permanent pegging on this section. Before any permanent work could be started practically a year was taken on temporary work. From Tahora the first thing that strikes the visitor is in fact that the line from there to the Flat has sharper curves and steeper grades than amain line. This is only a service line to give access to the Flat and the work ahead. After touching on other matters, the engineer stated that transport is an exceptionally heavy item on these works and any means whereby it was possible to lessen the cost was made full use of. Material to go to Mangaone travelled first by service tram second by jig, third by electric locomotive and fourth by motor lorry. Over the third ridge plans were ready and work was about to start on another jig which rose 730 feet above formation level and had a distance of 40 chains on each side.

In the workshops is machinery enabling engineers to cope with repairs and other jobs necessary in the efficient running of the works. A welding plant had now been included and was proving its worth. Metal for concrete, ballast, etc., had been procured from the department's quarry at Te Wera. To land this over in the Mangaone Valley for Nos. 2 and 3 tunnels and for further ahead, the cost would have been heavy and the transport also difficult. So the department must be considered fortunate in locating an excellent shell rock quarry 20 chains from the line in the Mangaone Valley. A crushing plant was installed on the line and the quarry was in full swing. About 1000 cubic yards had been crushed and delivered to the tunnels in this valley at a cost equal to the cost of Te Wera metal landed at the Flat. With metal cut out, transport to Mangaone consised mainly of cement and stores. Little permanent earthwork had been done on the Raekohua' section as yet, the principal work being in preparation for concentration. The line ran down the Raekohua Valley for 34 miles, where the stream, the road and the railway vied each other dominance. The railway took precedence while the road was made to pass belaw and above it in several places. The Raekohua Stream had been made to give up its bed in four places where it was shifted from its course by diversions.

There were two tunnels on this section, one six chains and the other 11 chains long. The approach of the last was completed and the tunnel would bes commenced soon. All overhead bridges had been completed as had been the concrete pier's of all railway bridges with the exception of the Tangarakau Stream bridge. The large culverts on the section were completed and all except one stream diversion had been made. A start had been made excavating

the cutting and forming the large bank for the station yard on the Flat and two platelayer's cottages had been erected. The section would shortly be in the position of having all minor works completed to enable the earthwork and platelaying to be pushed ahead rapidly.

The entrance to No. 1 tunnel was on a curve and its length was 31 chains. The first length was completed in July 1926, when it was estimated that it would be completed in March, 1928. For some time it was possible to work this tunnel from only one end owing to the heavy work on the Mangatatoko Valley. The two ends met on March 15. The levels, chainage and alignment were found to be correct. A total of 3750 cubic yards of metal, 2,20 Ocubic yards of sand and 650 tons of cement were used in this tunnel.

The next tunnel, No. 2, 54 chains long, was on the straight, and the west end was started in May, 1927, and 131 chains completed. Work on the east on the Managone Valley was started in November, 1927,, and to date 41 chains had been completed. This tunnel was to be completed by June 1929. No. 3 tunnel, 64 chains long was started from the west end in Managone Valley in January of this year and two chains had been completed. The heaviest earthwork in the Mangatoto Valley was a cutting of 103 feet centre height and six chain's in length, containing upwards og 50,000 cubic yards. Spoil from here was dumped to the bank in the stream alongside. This bank would require 70,000 cubic yards of spoil. To make a better bank and to push ahead material, a trestle was built over the stream. This trestle, built mainly of bush rickers, was 80 feet high at the highest point and six chains long. The bank was well on the way to completion, the spoil from the large cutting being augmented by spoil from the two tunnel faces in the valley. Before spoil could be tipped into this bank the stream had to be diverted.