Harding (Past President) congratulated the Authors on having developed such a sophisticated machine. It was encouraging to think that this experience was available so that if a Channel Tunnel project was started a British firm could compete with rivals in offering boring machines. 108.During the study on the Channel Tunnel, Mr Harding had visited a number of tunnelling operations where the tunnelling machines used had been the K and M Drum Digger, the Marietta in the French coal mines, two Robbin's machines at Oahe in South Dakota, the Bretby machine, the tunnels at Mangla bored by Robbin's machines, and the Robbin's machine on the Metro extension in Paris.109. He did not agree entirely with the Authors in the suggestion that the main problem was the hardness of the rock. This could be overcome by spending enough money. What mattered was the nature of the ground, whether it was folded or fissured or full of water, or whether it changed suddenly from rock to soft ground, as well as the diameter and the length of tunnel which were functions of great importance.110. The Robbin's machines at Oahe were 32 ft 6 in. in diameter and all the auxiliary machinery was housed in a steel box about 8 ft clear of the invert; this was in two levels with conveyors above and hydraulic and other electric machinery below. The material was composed of alternate beds of shale and sandstone. 111. In earlier models an outer face rotated in an opposite direction to an inner face, but this had been discarded in favour of single rotation. The machine was * Proc. Znsin civ. Engrs, 1965, 30 (April) 649-674. 170 Downloaded by [] on [11/09/16].
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