RAILWAY DEVIATION.

New Zealand Herald, Volume LXIV, Issue 19676, 30 June 1927, Page 10

RAILWAY DEVIATION.

WORK IN PUREWA TUNNEL. GOOD PROGRESS MAINTAINED COMPLETION NEXT FEBRUARY. INSPECTION BY STUDENTS. Of tho 1954 ft. distance of the large Purewa tunnel only 800 ft. now remains to lie completed. This gap is being bridged from both ends at the rate of 100 ft to 110 ft. a month,, and Mr. It. A. Packwood, the resident engineer of Public Works in charge, now estimates the work will be finished about the end of February. In that case it will have occupied altogether approximately two and a-half years. There are between 500 and 600 men employed about the tunnel, and an effective system embracing every detail of the work is thoroughly established. A group of 60 engineering students from the University College, who were taken over the works by Mr. Pack wood yesterday, showed the keenest interest in all that was going on and followed Mr. Packwood's explanations with very close attention. From Campbell s Point the party was conveyed in a public works train along the temporary line to the tunnel. Technical details of an unusual type cf bridge in Judge's Bay were explained to the students, and crossing Hobson's Bay they had opportunity of seeing in operation the ingenious travelling bridge which, g"ing in advance of the earthworks, enables a whole rake of trucks to be tipped at one time where otherwise they would have to be emptied singly.

From the large Orakei cutting already 250.000 cut of the total 350,000 cubic yards of spoil have been removed. It makes exce-1 lent filling and lias provided about a third of the adjacent railway embankment.

As the train crossed the Orakei basin the curious movement of subsidence and upheaval could be very clearly seen. The weight of the embankment has had the effect of forcing the soft bed of the basin upwards for a considerable distance on each side of the embankment. The excavation work at the approach to the tunnel f:om the Auckland end has been going ahead apace, and the workmen are now breaking through into the crater that was hollowed out immediately above the main tunnel entrance. The crater is approximately 100 ft. deep and from it has been trucked away 50,000 cubic yards of spoil, or about a quarter of the content of the whole cutting. The work of excavating the cutting and the tunnel has been proceeding simultaneously and it is estimated they will be completed at about the same time. At the face of the top heading from the Auckland end the students had explained to them the whole system of driving, timbering and concreting, ventilation and blasting, with the reasons for the various methods used; and they had ample opportunity to have their questions answered. The bins and concrete mixer, weighing up to 400 tons and built immediately above the tunnel entrance, were carefully examined. Afteu hospitable entertainment had been provided at the camp dining room the students eagerly seized the opportunity to inspect the Westfield end of the tunnel, 3',id here they found another stage of t!,'; complicated process in progress. The pressure here has always been very heavy and the presence of "greasy back r ' has added to the engineering difficulties which, however, have been mastered in decisive fashion.