Steve B Posted February 5, 2011 Share Posted February 5, 2011 What is the standard or minimum tunnel portal height for tunnels built say, 1920-1950? I'm looking at the Woodland Scenics single portal and it seems to have a lot too much height over the top of the loco and wagons. Thank you Steve Link to post Share on other sites More sharing options...
RMweb Premium Kris Posted February 5, 2011 RMweb Premium Share Posted February 5, 2011 Minimum height would have been the loading gauge which was 13'6" over rail height, but almost all tunnels and bridges would have been a little more than this. Link to post Share on other sites More sharing options...
RW James Posted February 5, 2011 Share Posted February 5, 2011 Woodland Scenics tunnel portals are designed to pass the NMRA gauge which is 21'9" or or 3 inches in HO. It is meant to clear all modern equipment - many of which were not in service for the period you are modeling. Keep in mind that the US standards are a lot bigger than the British loading gauge. Link to post Share on other sites More sharing options...
RMweb Gold TheSignalEngineer Posted February 5, 2011 RMweb Gold Share Posted February 5, 2011 Minimum height would have been the loading gauge which was 13'6" over rail height, but almost all tunnels and bridges would have been a little more than this. Bridges and tunnels should preferably be 12" above the loading gauge for steam, diesel or 3rd rail electric, (i.e. 14' 6") or 15' 6" for overhead electrified lines. Most tunnel profiles were curved, so the height at the centre would be considerably greater. A crown in excess of 20' above rail level would not be unusual for a double track tunnel. Link to post Share on other sites More sharing options...
Steve B Posted February 5, 2011 Author Share Posted February 5, 2011 Woodland Scenics tunnel portals are designed to pass the NMRA gauge which is 21'9" or or 3 inches in HO. It is meant to clear all modern equipment - many of which were not in service for the period you are modeling. Keep in mind that the US standards are a lot bigger than the British loading gauge. Thank you, that now makes much more sense. Time to take the saw to them. Steve Link to post Share on other sites More sharing options...
Peter Bedding Posted February 5, 2011 Share Posted February 5, 2011 Tunnels were usually required to support a far greater vertical load than the usual bridge. Thus the brick arch would be a geometric ellipse above ground (with a corresponding structure below rail level). The minor axis of the ellipse would be horizontal, placed to allow side clearance for the rolling stock. The major (vertical axis) would be chosen to cope with the nature of the soil/rock through which the tunnel passed. Vertical loading gauge standards would not normally apply. One obvious exception is the cylindrical section of the deep-bored Tube lines of the LT Underground. Perhaps we shall now learn of others! PB Link to post Share on other sites More sharing options...
RMweb Gold TheSignalEngineer Posted February 5, 2011 RMweb Gold Share Posted February 5, 2011 One obvious exception is the cylindrical section of the deep-bored Tube lines of the LT Underground. Perhaps we shall now learn of others! PB I wouldn't swear to it, not having the measurements, but IIRC the western portal of Woodhead looks as if it could be circular. Link to post Share on other sites More sharing options...
Fat Controller Posted February 5, 2011 Share Posted February 5, 2011 Tunnels were usually required to support a far greater vertical load than the usual bridge. Thus the brick arch would be a geometric ellipse above ground (with a corresponding structure below rail level). The minor axis of the ellipse would be horizontal, placed to allow side clearance for the rolling stock. The major (vertical axis) would be chosen to cope with the nature of the soil/rock through which the tunnel passed. Vertical loading gauge standards would not normally apply. One obvious exception is the cylindrical section of the deep-bored Tube lines of the LT Underground. Perhaps we shall now learn of others! PB Tunnels drilled by Tunnel Boring Machines are necessarily of circular cross-section- the Channel Tunnel, for example. In the case of manually-bored tunnels, the 'invert' (the corresponding structure below rail level) is vital to the integrity of the structure when present. Link to post Share on other sites More sharing options...
RMweb Gold unravelled Posted February 6, 2011 RMweb Gold Share Posted February 6, 2011 Sometimes the portal was larger than the bore, and there would be a tapered section to match it up to the main tunnel. While this was probably to give a grander visual impression, it's interesting that some tunnels on high speed lines are being built similarly, (I think to reduce pressure effects?). Perhaps the original engineers were ahead of their time. Dave Link to post Share on other sites More sharing options...
PWSlack Posted February 6, 2011 Share Posted February 6, 2011 The minimum height for a structure over the railway is determined by the Standard Structure Gauge, examples of which have been converted to dimensions needed by the modeller by the various specialist scale societies and published in their manuals for their subscribers to use. For a modern line built in 12in scale, the answer is 4540mm above rail height for British practice. Simply divide the scale into the 4540mm to obtain the minimum overhead clearance. For example, for 1:43.5 scale, the minimum rail-to-underside-of structure dimension is 4540mm/43.5 = a little over 104mm. Link to post Share on other sites More sharing options...
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