Engineering Wonders of the World
Volume I

302 ENGINEERING WONDERS OF THE WORLD. shield used on the Hampstead and Piccadilly Tubes. On both these rail- .1 ne ways consid- S erable lengths Efficiency. ® of tunnelling were executed with remark- able success by means of rot- ary excavating machines of the type shown. At first, especially on the Hampstead Tube, considerable difficulties occurred in driving the shields satisfactorily to line and level, and their speed was very slow. In fact, it looked at one time as if the tunnels would not be constructed either sufficiently fast or accurately to warrant the retention of the rotary type of machine. Consider- able lengths of those tunnels constructed during the early period of the work had actually to be adjusted as regards both line and level before they were finally accepted from the contractor. Fig. 8.—price’s ROTzXRY digger, front view, b,b, buckets; c,c, chisels. Later on, however, after the rotary shields on the Hampstead Tube had been fitted with conveyors, their speed rose in September 1903 to sixty - eight rings as the maximum per week on any part of the work. Towards the end of November 1903 the very first attempt to drive a rotary machine round a sharp curve was made on the section of the Piccadilly Tube between Brompton Road and South Kensington, where a shield for a 12 rally tried the mechanism a good deal—so feet 7 inches internal diameter tunnel was started round a curve of from 7 to 8 chains radius. Some little difficulty was at first experienced in steering the machine, although it was provided with graduated guide rods, etc., but ultimately it was kept well under control by observing extra care in driving. The gradual growth in the'number of rings laid in a week from about forty to eighty induced fresh rivalry among the men, as every new record made was soon known at all points where the several shields were work- ing, The machines were pushed for all they were worth. This Gradual Increase of Working Speed. great increase in speed natu- much so that both the rotary machines being driven from Golder’s Green towards Hamp- stead, after reaching the bottom of “ the Avenue ” by the Heath, had become so strained that it was found necessary to take them out and rebuild them entirely. The working faces were at that time over 2,000