ws.eternal-september.org> 34689fff   
   XPost: uk.railway   
   From: recliner.ng@btinternet.com   
      
   Phil Kane  wrote:   
   > On Wed, 27 Dec 2017 13:12:58 -0000 (UTC), Anna Noyd-Dryver   
   >  wrote:   
   >   
   >> After the old track and sleepers are removed, it appears from that picture   
   >> that the old ballast is being removed too, following which I would guess   
   >> that better drainage will be installed, then there's usually a membrane of   
   >> some kind to keep the sub-soil out of the ballast, this will be followed by   
   >> the new ballast and finally the new sleepers and rails.   
   >   
   > Thank you very much for that explanation of the work to be done.  What   
   > is not evident to me from the picture is whether the line was on   
   > elevated structure, on the surface, or underground - the last two   
   > would entail digging.   
      
   No, the digging would be needed regardless of whether the line was   
   elevated, on the surface or underground. It's to remove the life-expired   
   ballast, not to excavate a new track bed. This line has been here for   
   almost 150 years, and the digging isn't to change its level.   
      
   > I am one-third of the way around the world and   
   > don't remember those details from my one and only visit to London 50   
   > years ago!   
      
   As is clear from the photograph, the four tracks are in a cutting at that   
   location. It's a very busy sub-surface line that runs just below street   
   level in central London, but the tracks are in an open cutting where the   
   track replacement work is going on.   
      
   When first built in the late 1860s, the lines in that area were all in the   
   open, but many buildings were soon built around and over them. A few   
   stations to the west, the tracks are elevated, and further east, they're   
   mainly covered, but never far below street level. There is also the deep   
   tube Piccadilly line running directly below those sub-surface tracks.   
      
   The sprawling District line has several routes that all share that short   
   length of four-track line:   
      
      
      
   New automatic signalling and train control is being installed that will   
   make those tracks busier than ever, which might have necessitated the track   
   and points replacement work.   
      
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