RELINING A TUNNEL

Sun (Auckland), Volume 1, Issue 100, 19 July 1927, Page 14

RELINING A TUNNEL

WORK AT KARANGAHAKE ELIMINATING DANGER A start was made recently to reline the Karangahake tunnel, which is five miles from Paeroa on the Waihi line. For some time past the tunnel, which is 535 chains long, has been gradually caving in and giving the railway authorities some trouble. Recently it got within three inches of the loading gauge, and it was found necessary to reline it as it would soon have become dangerous. Mr. W. T. Langbein, assistant engineer, Auckland, has just returned from the tunnel, where he has been attending to the repairs which must be done. Work can be done only at night, the men starting at 7 p.m. and working till six o’clock the next morning. It will take three months to complete the reconstruction. Strong supporting rails have been put in the tunnel so that the old lining can be chipped out. The new lining to the tunnel will consist of concrete reinforced with 401 b. rails at 2ft. centres. The work is arduous and difficult. Mr. Langbein has devised a special truck on which the concrete is mixed in the tunnel. This truck carries the necessary ingredients for the concrete, a mixing platform and a tier of steps, so that when the roof of the tunnel is reached there will be less distance to carry the concrete.

Explosives cannot be used in the tunnel because of danger of bringing it down, and drills are being used to cut out the old lining. Mr. Langbein is of opinion that the hill through which the tunnel runs is of soft rock, which, by water trickling through it, has expanded and so forced the sides of the tunnel outward.