ORONGORONGO TUNNEL PIERCED
GANGS MEET AT WEEKEND
OVER TWO MILES THROUGH SOLID ROCK
ENGINEERS’ CALCULATIONS WORK OUT EXACTLY
The piercing of the Orongorongo range by tunnel was completed on Saturday, when the gangs working from either side met after a big simultaneous explosion broke through the remaining few feet of barrier. The calculations of the engineers are reported to have worked out almost exactly.
On Friday last it became obvious that the two faces of the Wainui–Orongorongo tunnel were so close to one another that it was decided, instead of blasting alternately, to have a simultaneous shot — that is, a shot of 13 holes on either side, hoping that the shattering force of the double blow would break down the last barrier between the two gangs of tunnellers.
A Successful Shot
The shot was fixed for 2 p.m., and when the fumes had cleared away sufficiently for the men to see the result, there was a ragged hole in the wall of blue rock big enough for a man to crawl through, and from the one side the men could see approaching the figures of their fellow-workmen on the other, and they shook hands through the hole. It was virtually the end of the longest tunnelling job done in the Wellington district for half a century.
“Down Tools”
As the “break-through” had been accomplished, and it was Saturday afternoon, it was a case for “downing tools” for the weekend. One of the tunnelling party (Mr. P. Webb), who was proceeding to the city, met Mr. J. M. Morice (the water and drainage engineer) on the Hutt Road, motoring, and conveyed to him the news of the “break-through.” Mr. Morice at once decided to pay a visit to Wainui and inspect the levels, which always interest the engineering mind.
The First Man Through
When questioned as to how the levels were, Mr. Morice, the first man to traverse the tunnel from end to end, other than the tunnellers from Orongorongo, said that he had to climb through the hole in the rock, and that a good bit of rock remained to be lifted out before the floor of the tunnel was revealed. Mr. Morice admitted with characteristic caution that the levels “appeared to be pretty right.”
Levels Exact
“The levels were exact!” declared Mr. Robert Semple, the leader of the corporation gang of tunnellers, who undertook the big job. He could not say so much to an inch, but the effect of the last double shot showed how accurately the engineers had worked out their calculations, for it had to be remembered that the tunnel was no short drive, but one of over two miles in rough country of unknown formation. The hard blue sandstone which was met with almost the whole way through prevailed up to the last shot, and no timbering would be required in the section where the two parties met.
Some wet places were found here and there, where heavy timbering was necessary, and this work was done with the utmost care, as on the strength and efficiency of such supports in soft country depended the lives of the men.
A Unique Achievement
Of no feature of the work is Mr. Semple prouder than the fact that right from the beginning to the “break-through” no serious accident had occurred. He claims it as a unique record and something for co-operative as against contract labour. Lives in plenty had been lost at Otira, Mangahao, Mount Victoria, and recently on a Government job in the north, but beyond bruised fingers and grazed hands there had been no serious accident at the Orongorongo job, where it was the men’s duty to care for themselves and leave nothing to chance.
Another Record
Furthermore, Mr. Semple claims that his men have put up a record in tunnel driving on time. It will be remembered that at the time the City Council wished to commence work on the tunnel there was a very pronounced shortage of men, as the country was still feeling the effect of the war. At that time Mr. Semple, an experienced miner and tunneller, put up a proposition to the council to do the work at a certain price, guaranteeing no delay through strikes or anything of the kind. After considering the matter the council, on the recommendation of the late city engineer (Mr. W. H. Morton), resolved to accept the Semple offer, though it was admitted at the time the cost was high.
Having secured the job, Mr. Semple assembled his men, and a start was made to break ground on the Wainui side of the Orongorongo range on December 6, 1920. But this was not the real start, as there was the preparatory camp-building, and, as no power was available for the rock drills, it was all hand steel work for the first 218 ft. of the Wainui cone.
For six months a number of men were employed in making a rough bridle track over the Orongorongo range, which is 2,800 ft. high. All those who have made the journey are aware of the arduous nature of this work, where in places a path had to be cut on the sides of mountain abysses through virgin forest at an elevation sufficient to command a view of the Wairarapa Lake and Palliser Bay and Cook Strait beyond.
Then with the aid of water from the Morton Dam, a power station was provided at Wainui, which gave plenty of power for the air-compressor rock drills, and also for the supply of fresh air at the face, and electric light for camp and tunnel. As soon as the power house was available three shifts of eight hours were employed on the face. That was from October 15, 1921.
Long Trek to Orongorongo
But it was not so easy to provide such facilities on the Orongorongo side, to which no road led, and no easy place presented itself. There was the spot, in a chasm-like heavily timbered valley across a 2,500 ft. high range. The bridle track was all right for the packing of flour and meat, but was impossible for heavy weights. For a year four-horse teams laboured over the Wainui Hill, down the valley, round the sea shore into the Orongorongo Valley, and so up the torrent-ripped gulch, to the point opposite Morton Dam.
Then came the task of building the intake dam and filter basin, laying the pipes from there through a short tunnel to the site of the power-house, near the Orongorongo entrance to the tunnel. By September 28 of that year the water was flowing through the 21-inch pipes and the motors were droning steadily. From that date fine progress was made, and three shifts were soon at work.
The Total Time
Reckoning from the day power was supplied on the Wainui side, the time occupied in making the 7 ft. square drive was two years and four months, but had the power been available on both sides at the same time, even that time would have been markedly lessened. Mr. Semple says there are several days’ work yet for his men to clean up at the “break-through,” but they should be all out of it before the end of the week.
In the dismantling of the machinery on the Orongorongo side it will be possible to bring the greater part of it — if not all — through the tunnel by truck, which will effect a good save in haulage.
As soon as the tunnel is “squared out” at the break-through it will be possible to connect up the two ends of the 21-inch pipe, which is to convey the water through the tunnel (and which during the work has been used as an air shaft). This pipe will eject the water into George Creek (which flows into the Morton Dam), but next year it will be connected up with a new main that will conduct it direct to the Karori reservoir.
Councillors to Visit Tunnel
The Mayor (Mr. R. A. Wright) will not return from the south until tomorrow, but it is probable that on Wednesday or Thursday he and the members of the council will visit the tunnel.
MR. SEMPLE’S OPINION
“We have actually been boring for two years and five months,” said Mr. Semple. “Out of that time, one of the ends was going for 12 months. Had both ends been working, we would have finished in two years — at the rate of a mile a year.
“The levels were absolutely accurate, and not an inch out. It is a tribute to the efficiency of the city engineering survey staff — Mr. Swinburne and his assistant, Mr. Campbell, who are to be congratulated on a very fine achievement.
“We have no accident to speak of, nor any stoppage, during the whole of the job. I am delighted with everything connected with it. The men worked loyally and well together, and, in my opinion, it is a triumph for co-operation.”
Mr. Semple added that, after a week or so spent cleaning up, when the tunnel was passed for final inspection he would make a general statement regarding the work.
