Slight Delay In Tunnel Blasting At Lyttelton

Press, Volume CI, Issue 29763, 5 March 1962, Page 12

Slight Delay In Tunnel Blasting At Lyttelton

Because of the stones unexpectedly scattered over a wide area around the Lyttelton portal of the road tunnel by blasting on Friday, general operations would be held up for a few days while small experimental charges were detonated, the project engineer (Mr J. G. Smith) said yesterday. The first full-sized blast to form the portal was scheduled for Saturday, but had to be postponed because of the untoward effects of the preliminary blasting, said Mr Smith.

“We shall have to ensure that we do not send any more stones flying around in the built-up area,” Mr Smith added. “Unfortunately, blasting is an art and not a science. We sliall have to fire a few small charges to see which way the rock wants to break.” The purpose of the work at the Lyttelton end was to provide a pilot tunnel which would improve the ventilation in the main workings, and to put in a short distance of full-width tunnel to make sure of safety in the main workings when they approached completion. Probably only about 25ft of full-width tunnel would be needed, said Mr Smith, as the indications were that the rock was quite good. If the rock proved to be weaker than was thought, the tunnelling would be taken to a greater distance. The pilot tunnel would be about Bft high by 6ft wide, which was about the smallest cross-sectional area in which a man could work with comfort. These measurements compared with 32ft wide by 31ft high for the completed tunnel. The pilot tunnel was expected to meet the main tunnel during June. The pouring of concrete for the tunnel walls had started, and was proceeding slowly, said Mr Smith. The work would go much faster when special forms just arrived from England were put into service. This would be in about 10 days’ time after the forms had been given necessary modifications and assembled. Work had started on the fanhouse, which would strad-

die the Heathcote portal. Difficulty was being met in reaching solid rock for the foundations. One side was satisfactory, but blasting was under way on the other side and would probably continue for several more days as it was expected that the excavations would have to go down 10ft to 12ft.