The Arthur’s Pass Tunnel

Progress, Volume XI, Issue 6, 1 February 1916, Page 549

The Arthur’s Pass Tunnel

Progress of a Big National Undertaking

After many initial difficulties and delays, the Public Works Department have brought this big work to measurable distance of completion.

The Arthur's Pass Tunnel, carrying the midland railway through the Southern Alps, was to have been completed in February 1912, the original contractors, Messrs McLean and Co., having undertaken to finish it in five years. It is still among the list of

unfinished works, but it is satisfactory to note that the distance remaining to be driven has come down to one mile forty-four chains, and that in a little over two years, the monumental task of the engineers will be complete, and a splendid route opened up between the fertile plains of Canterbury and the rich mineral resources of the West Coast.

Since the private contractors gave up the contract in December 1912, the Public Works Department's engineers, under Mr. R. W. Holmes, M.T.C.E., chief engineer, have had control of operations. Driving goes on as fast as possible, the only limitation being the supply of skilled labour, All the in-

itial difficulties have long since been overcome, and now it is simply a matter of steadily driving headings, "breaking out" the rock, and lining the fullsized tunnel at the rate of a steady five chains per month.

It was expected that the tunnel would cost £599,000, this being the contract price but that figure is bound to be exceeded in view of the fact that the contractors, after doing work and providing plant of a total value of £249,882 found the job too expensive to be finished within the stipulated price. A Parliamentary Committee looked into the whole position before releasing Messrs McLean and Co. from the contract, and came to the conclusion that as the Otira Tunnel is a national work which ought to be completed, fresh tenders should be called, and the Public Works Department instructed to continue the work meanwhile, It was fairly evident that no

private contractor would face the task which the original contractors had found so difficult, consequently the responsibility for the work was shouldered by the Public Works Department, which has at last brought it within measurable distance of finality.

Most work has been done at Otira, or West Coast end of the tunnel, where two and. a half miles have been fully completed, while the advanced headings have been driven a further twenty-four chains.

At the Bealey end, the completed portion is seventy chains —just short of a mile — and advanced headings have been driven a further seven chains. Thus the position in brief is as follows: —

dip; at Otira they are up-grade. The tunnel when completed will drain down to the West Coast side.

Ventilation is afforded by a system of exhausting the air from the face, pure air being thus induced through the completed part of the tunnel. When the work was first planned, ventilating was done by releasing compressed air at the face, thus driving out the impure air along the tunnel. This meant the fouling of the line along which spoil has to be hauled, and a change to the exhaust system was made by the Public Works engineers.

Electric mine locomotives are used for haulage at both ends. We illustrate the type, which takes

Miles Chains Total length of tunnel .. 5 25 Lengths completed .. 3 61 Remaining length to he driven 1 44 Those who expected some interesting geological discoveries as a result of the big drive through the range have been disappointed. The rock has been monotonously alike right through, varying only in degree of hardness. At the present headings, the “ground” as it is technically called, is hard, which is a favourable condition for the work. As a result, the advance headings have been pushed on at an accelerated rate. The system of working is to drive two headings, one at bottom, and the other at top level. Then the intervening rock is taken out, and the tunnel lined with concrete. At the Bealey end, the workers are driving on the

power from a bare trolley wire and has given complete satisfaction. Water is' available for power purposes at both ends of the tunnel, but it has occasionally to be supplemented by steam at Otira. One of the engineering tasks associated with the big work is the protection of the rail approaches at Otira from the Rolleston River, which runs at a terrific pace in flood time. Groynes were built of boulders, faced with concrete blocks weighing sixty tons. We illustrate the groynes opposite the junction of the Otira and Rolleston rivers. It will be noticed that the huge blocks at the end of the nearest groyne, have been displaced by floods, and that the outermost has sunk a good deal. This is in accordance with anticipations. As the current undermines the blocks they sink, and are then built up, until a solid lasting foundation is made,