From: stephen@sprunk.org   
      
   On 05-Oct-14 14:47, Adam H. Kerman wrote:   
   > Stephen Sprunk  wrote:   
   >> On 05-Oct-14 12:51, Overmod (Robert M. Ellsworth) wrote:   
   >>> https://www.scribd.com/doc/241718975/NYC-Tunnels-Assessment-Report   
   >>   
   >> Not interested in giving them a bunch of personal information just   
   >> to read what _should_ be a public document.   
   >   
   > User: buggsme1; password bugmenot   
      
   Thanks.   
      
   >> What does "top-down track system" mean?   
   >   
   > In direct fixation, it means top of rail and gauge are established to   
   > the specification, then the fasteners are attached, then the concrete   
   > is placed last. That really makes a lot of sense, because there's   
   > just the one step at which things are calibrated. Bottom up requires   
   > a lot more calibration.   
      
   Ah, okay; I hadn't seen the term before, but that makes sense.   
      
   > Doesn't explain how they get the concrete underneath it all (very   
   > carefully).   
      
   Pour it between the rails and smooth it out?   
      
   >> I'm a bit surprised they're still using ties on ballast inside   
   >> such important and high-volume tunnels; direct fixation has been   
   >> the norm for decades, and from the sound of it, they wouldn't have   
   >> had these problems.   
   >   
   > Uh, whatever, Stephen. Of course you know for a fact that the timber   
   > amd ballast work was botched and failed to maintain gauge and desired   
   > top of rail when installed. Your 20-20 second guessing is always   
   > superior knowledge to anyone's first-hand experience of the quality   
   > of the original work.   
      
   WTF are you going on about?  I said nothing about any of that.   
      
   > If you read the report, it doesn't say there's anything wrong with   
   > ballast, but it's not done that way today.   
      
   Ballast and ties are not inherently bad, but the cost of maintenance   
   (including the cost of service outages, not just materials and labor)   
   must be balanced against the cost of installation.   
      
   Tunnels and bridges are also special because you _already_ have a solid   
   floor to build up from, plus you can't use concrete ties because they   
   quickly grind the ballast to dust; you have to use wooden ties, which   
   have a higher maintenance cost--and that is apparently what tips the   
   scale to direct fixation in those areas, whereas ties and ballast are   
   still (for now?) the norm in other areas.   
      
   > The ballast must be removed because it's coated with chloride,   
   > which sure as hell sounds like water infiltration and drainage   
   > which, last I looked, are problems that direct fixation of rail   
   > has fuck all to do with correcting.   
      
   Direct fixation means no ballast, so there would be no opportunity for   
   such a problem to exist in the first place.  That was my point, which   
   (as usual) you deliberately ignored so you'd have an excuse to argue   
   with me.   
      
   I assume they'd still want to clean the tunnel walls/floor to prevent   
   other problems, but washing smooth surfaces is a lot easier than washing   
   ballast.   
      
   S   
      
   --   
   Stephen Sprunk         "God does not play dice."  --Albert Einstein   
   CCIE #3723         "God is an inveterate gambler, and He throws the   
   K5SSS        dice at every possible opportunity." --Stephen Hawking   
      
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