OTIRA TUNNEL.

Dominion, Volume 7, Issue 1957, 14 January 1914, Page 8

OTIRA TUNNEL.

SHOULD BE OPENED IN 1919. BTEADY PROCRESS. DESCRIPTION OF THE WORK. ' ) (By Telegraph— Special Correspondent.) Christchurch, January 13. Work on tlio Otira Tunnel was recommenced last week after the. NonYear holidays, tlie Public Works Department carrying on the operations. The tunnel has been driven in about threequarters of a mile- from the. Boaley end, mid tho embankment is formed from the spoil (writes a ".Vews" representative), l'hero is a decided down grade from the eastern,end of tho tunnel, and this fact accounts for the bother that has been .experienced from tho water soakage. Surface water collects in an annoying manner, and a very elaborate system of pumps Ms been rigged up to doal with this accumulation, which unless removed would quickly put a stop to all work at the inner face of the tunnel.

The works at tho Otira, or western, end of tho tunnel aro of far greater sizo than at tho Bealoy end, and at present roughly about eighty men aro being employed in tho tunnel. Up to tho present the depth of the drive is about two miles and a quarter, and the work is proceeding steadily. Much trouble has been experienced at) the western ■ end from water, but the fact that there is a big fall from the face to tho tunnel's mouth has simplified matters. Pumping does not have to be resorted to, and the water comes away through a covered concrete drain in the floor of tho tunnel. Tunneling In Bad Cround. Tho tunnelling is now in very bad ground, and has been for some timo. To start with, the going was through solid rock, which caused practically no trouble, but latterly the courso of the work ■ is through rock, which at somo timo or other has been disturbed by somo upheaval. Fissures and cracks, filled with a sort of cement-like substance, run in all directions, and it is not good holding ground at all. Tho working face of the tunnel is estimated to be just about underneath Pegleg Creek, which the traveller crosses nearly at the top of Arthur's Pass, and tho water from this creek filters down through the fissured rock into the tunnel far below, washes out tho cement, and causes the rock to become unstablo and dangerous. Tho consequence is that the utmost care has to be taken in all the tunnelling operations, and tho work is rendered rather slow and also rather more expensive than was anticipated. Wet and Uncomfortable Work. The whole of the interior of the drives has to be timbered, as the work proceeds, and then, when the whole face has been taken out to tho required size, it has to bo lined,with heavy concrete blocks to prevent any possibility of a fall of rock. Tarred felt protective coverings have to be laid between tho natural rosk. and the concrete lining blocks, to prevent the water from percolating through and washing out tho joints of cement between the blocks, while lower down tho walls are provided, with large "wcep-holes" to allow the water to escape into the tunnel drain. The method of tunnelling is ono that allows the largest possible number of men to bo at work at one time. Tho whole faco is not taken out at one operation, but a drive eiglit feet high is niado into tho lower part of the face. Thie is timbered as it proceeds, and when tlio spoil has been removed, the roclcabove it is taken out. The wooden "roof" of tho first. drive serves as tho floor of the upper one, and all the srroil can be shovelled into the trucks, which aro run in underneath, with a minimum of exertion. Then the sides aro taken out in sections, while the original drive is carried on into the rock. The gangs of men can thus work in "layers." Ono lot will be driving ahead, another lot will lie timbering, yet nnotlicr lot will bo taking out the sides, while the rear is brought up by the men facing the tunnel with concrete. It is exceedingly wet and uncomfortable at tho tunnel faco, and the laboriousness of the work may bo realised when it is said that the men only work six-hour shifts, though' they are paid for each shift as though they had worked eight hours.

The Engineers Never Know,

The rottenness of tlio ground in which work is proceeding at present is the cause of much additional labour and lost time. When a charge- of explosives is fired, the engineers never know whether tlio correct Quantity of material will be brought down or whether there will bo a..regular rock slide. If the latter occurs,.;:!, big gap is left, which,- if not filled up, would mean that there would bo a hollow behind the concrete easing. Obviously this could not bo allowed, and often extra time and money have to bo spent in carefully packing up these hollows again with rock so as to mako all solid. Nevertheless the work is going steadily on, and it is estimated that at the present rate of progress the ceremony of opening the lino should take in 1919.