CRACKS IN TUNNEL.

Auckland Star, Volume LXX, Issue 15, 19 January 1939, Page 6

CRACKS IN TUNNEL.

SOUTH MAIN TRUNK. AMURI BLUFF TROUBLE. "NO CAUSE FOR ALAKM." (B.r TeleKraph.—Press Association.) CHKISTCHUKCH, Wednesday. TTip Public Works De[>artinent authorities have been concerned over defects which ha\r occurred in the structure of the Mortheni end of the Am mi Bluff tunnel on I lie JSouth Island Main Trunk railway, but after an inspection to-day the .Minister of Public Works, the Hon. R. Simple, declared that there was now no cmiae for alarm. The Minister ha« set in train the necessary remedial measures, and for the rest of the job a new tunnel construction will be adopted which is expected to ensure safety from further trouble of the same sort. A short way in from the northern end of the tunnel there have appeared several cracks in the concrete lining along the vertical side*. The worst of theee fractures is many yards long and so deep that it is possible to insert a finger for nearly an inch. Further along the tunnel theix are smaller cracks. It i-i considered that these cracks have been caused by what i* known technically as a swelling of the strata in the country through which the tunnel in being bored, the swelling being caused by the strata being exposed to the air. In an interview after hi* inspection to-day, the Minister admitted that these developments had caused him serious concern, but he stated that now the tunnelling had reached a harder type of country there wa* less catwe for "alarm. Mr. Semple indicated that the tunnelling was expected to resume the routine schedule within the next week. Trouble at Both Terminals. The Amuri Bluff tunnel ie 43 chains in length, some 12 chains being driven on the northern end, where the cracks have appeared. Difficulty has also been experienced at the southern terminal at Tnrapuhi, where soft and clipping country has retarded progress seriously. Some tunnelling has been completed there, but it is in the form of a "tunnel that is. not a tunnel." for the structure is out in the open air, the enrrounding country having proved eo slippery that it had to be removed from the actual tunnel. Open country extends in front of and behind the completed section of the tunnel. "Our difficulties appear to be overcome M far as I can; we," Mr. Sample Mid, "and while there has been some delay because of the necessary change in design, the tunnellera should catch up on their ordinary echeduled speed and get back to normal in • week or so. The old design followed -was the ordinary tunnel design adopted in New Zealand •ad suitable for ordinary type* of rock with the usual vertical wall and semicircular arch.

"The new design has an anched wall instead of a vertical wall, with the arch starting from the footings. Thie design will be continued right through the Job, Mid wa will also increase the tbicknese of the concrete used and introduce reinforcement. The fractured sections will have to be pulled out and , reinforced or strengthened by reiaforced concrete ribs. Of course, unless the cracks show eigne of developiaini tb*r» WUI be to need for thlt t«W do* Immediately. It can be left :<yetil the tunnel is through. - 3r ;/ "There is no serious flange* at the moment, but the position has Bad us very much worried. Every effort will be made to get over this diAeultj and to keep the work ae near as possible to schedule. There is nothing to be alarmed at now."