THE OTIRA TUNNEL.

Manawatu Herald, Volume XXX, Issue 383, 9 May 1908, Page 3

THE OTIRA TUNNEL.

A Huge Undertaking. Five Miles Through the Hills. As mentioned in a previous issue, on Monday last, Premier Sir Joseph Ward fired the first shot in the above tunnel. It is the greatest tunnelling project in the Southern Hemisphere, and one of the six largest tunnels in the world. To be exact, the length of the tunnel will be five miles twenty-five chains twelve feet. It will be seventeen feet high and fifteen feet broad. It will be quite straight, with a dip from the east to the west. The eastern poital will be 2,435 feet above sea level, and the western nortal 1,585 feet, giving an incline in the live miles of 850 feet, or one foot in 33. Messrs John McLean and Sons have contracted to make the tunnel for ,£599,794. “ Fxtras ” will probably bring the total cost up to ,£600,000. It has been calculated by a person fond of figures that the tunnel will be 332,640 inches long, and it will cost nearly £2 an inch along its whole length. The workmen inside the tunnel will be, on the average 700 feet below the mountains, but at one spot, beneath Warnock’s Knob, they will burrow at a depth of i,roo feet. The conliaclors have already prepared their plans for the attack upon the ranges. Klcctiical appliances will be used to a great extent, and as a means to this end the water-power available will be brought into requisition. For the first lime in New Zealand Pelton wheels will be used in connection with tunnel construction. They will be operated upon by water, and will supply the power for hauling trucks, pumping air and water operating the drills, and supplying electric current lor lighting the tunnel. The Pelton wheel will be worked by the projection of a powerful jet of water against a large number of small buckets attached to the wheel’s periphery. The air percussion drill will be used instead of the hydraulic drill. It is thought to be the best drill for boring the haul slaty rock through which the tunnel will penetrate for most of its length. It is expected that exceptionally heavy demands will be made on the supply of water power at the Bealey end of the tunnel. Water will probably accumulate in the workings as the tunnel slopes from that end, and a powerful pumping power will be required, as the water will naturally flow downwards to the opening. Probably about 750 horse-power will be required at the Otira end for all purposes.

The tunnel, of course, will be bored from both ends, the gangs meeting somewhere near the middle. About two miles and a quarter will be done from the Bealey end and about three miles from the Otira end. The work ot ventilation alone will be an important undertaking, and in this respect the contractors are tied down to stated conditions. Air for instance, must be supplied at the working faces at the rate of 73 cubic feet per man per minute where blasting operations are necessary, and 30 cubic feet where there are no blasting operations. Each horse used in the tunnel will be given as much air as four men. With a complete plant of rock drills, boring steadily, many holes will be bored at one time, and there will be large blasting operations. The smoke and gases caused by these operations will be removed by exhaust tubes, and fine water sprays will be provided to absorb the gases. Although the specifications make provision in the case of horses being used for haulage, it is likely that some form of mechanical traction will be adopted. The working and living conditions of the workmen receive considerable attention in the specifications. At each end of the tunnel, and at any winzes, or small shafts sunk for ventilation, which may be driven, the contractors will provide waiting-rooms, clothesrooms, aud bathrooms, which will be warmed as required, and will be furnished with a sufficient supply of hot and cold water. The accommodation provided in this respect must be sufficient to meet the wants of all the men in any incoming or outgoing shift, within half an hour after they reach the portal of the tunnel. Within one month of starting the work on the tunnel these rooms must be completely finished and equipped. Ambulance and first aid equipment must be kept, not only at each portal, but at each working face. Outside the tunnel the contractors will house their men in huts, the sizes of which are regulated in the specifications.