Improvements in the Construction of Subterranean Tunnels and in Machinery therefor

26,804. Binnie, W. J. E. Dec. 20. Tunnels and tunnelling.-Tunnels are driven with the aid of a shield and lined with concrete which is compressed by the rams which also serve to advance the shield. Temporary rings C, D, E, F are built up inside the permanent lining as the shield is advanced, and the concrete is shovelled in between these rings and the tail end B of the shield and compressed in sections by the rams. When the concrete has set, the rings at the rear are removed, the upper sections C being dropped on to tracks L to bring them forward for re-erection. Short rail lengths M to constitute the track are attached to the lower ring segments E.