Gelignite Gouges Out Tons Of Rock In Bed Of Diversion Channel

Otago Daily Times, Issue 27265, 16 December 1949, Page 6

Gelignite Gouges Out Tons Of Rock In Bed Of Diversion Channel

Sun, wind and water through the centuries have carved out the gorge of the Clutha River above Roxburgh. But the slow erosion of the ages does not meet the urgent needs of human progress. Gelignite and giant machines are biting into the rocky bed of the gorge, gouging out a channel to take the sullen river while the engineers construct a barrage which will harness its power for the province. Roxburgh residents are becoming accustomed to the dull thunder of blasting charges echoing down the gorge, but yesterday afternoon they heard the biggest blast since the scheme commenced. About three-quarters of a ton of gelignite was exploded, smashing thousands of cubic feet of rock.

Weeks ago the labouring engines of the heavily-laden trucks had dragged tons of the soft surface layer of soil and gravel off the course of the diversion channel. Some of it was u3ed for building* up camp sites or forming roads; the rest was placed aside for later use. A series of smaller blasts has razed rocky outcrops in the bed of the cut. With the massive power shovels now assembled and working, heavier rock can be handled and blasting operations on an increasing scale have been commenced.

, Yesterday’s blast was the biggest so far, 17901 b of gelignite being used. An intricate network of fuse cable traversed the area at the upper end of the cut which was to be attacked. Dozens of drill-holes patterned and bordered the area to hold the plugs of gelignite and to control, as far as possible, the direction of the reck fission. To the men on the job it was just another blast, but to the laynaan it was an exciting and impressive operation. ' A better idea of the force of the blast could be gained from a close inspection of the mound of shattered rock. From* the bottom of the 15ft bore holes the whole roughly square area had been pulverised and piled. Pulverised is, of course, used in a comparative sense—rocks remained which were the size qtf a small car, but they would be attended to later. It was, however, only one of the many giant blasts which will be needed before the channel is completed. In fact, one of the engineers promised that there would be much bigger and better blasts before the job was through.

All morning the blasting crew had been lousy plugging the charge holes and laying the fuse, and by early afternoon the work was completed. There was a final check, and a prudent retreat to a safe distance up the hillside. Skill and experience in laying such majof charges determines to a large extent the direction and effect of the explosion, but there is still a certain element of risk with flying surface rock.

Three minutes was the safety margin allowed for the man responsible for touching off the blast. Looking down on the site, he could be seen setting the fuses and then moving with alarming casualness to cover. Slowly the seconds ticked by . . . one minute . . . two . . . half a minute to go.

Nevertheless, an explosion which shifts about 4000 cubic yards of rock is not to be taken

lightly. Meantime, the administration and living area is continuing to look less like a camp and more like a township. There is constant building in progress—stores , offices and homes. Lawns have been laid down to help mitigate, the constant dust nuisance, and in time the roads in the camp, will be sealed. Across the river neat little homes which will provide quarters for married men are being erected, and there is another camp springing up for single men. The reconstruction of the road from the Roxburgh Railway Station, along the east bank of the river, is nearly completed, and it will provide easy acess to the camp and construction site.

Then the rock erupted. There was a swift flash under the dust cloud, and an appreciable pause before the whiplash crack of the explosion sent its echoes rumbling and rolling like a man-made thunderstorm down the gorge.

A brisk wind caught the dust cloud before it had gained height, spread it and sent it scurrying off toward the camp. The last of the loose stones pattered down on the tumbled pile of rock which had replaced the comparatively smooth surface of the diversion cut. Already men were going about their normal tasks and the monster Euclids were groaning and protesting along the roads.