From: ahk@chinet.com   
      
   Stephen Sprunk  wrote:   
   >On 05-Oct-14 12:51, Overmod (Robert M. Ellsworth) wrote:   
      
   >>Perhaps a more informative reference is the copy of the actual report   
   >>that WNYC put up.  (This is a scribd document, so you may need to   
   >>register with them and provide other material before you can download   
   >>it):   
      
   >>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   
      
   >>The report notes that most of the damage is in the concrete bench   
   >>walls, and chloride intrusion into the crushed-stone ballast.  Imho,   
   >>the logical solution for the latter (as described in the report) is   
   >>to use a modern 'top-down' track system as a replacement; this might   
   >>also increase effective traffic throughput by allowing somewhat   
   >>higher speed, especially in the 'outbound' North River Tunnel bore.   
      
   >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.   
      
   Doesn't explain how they get the concrete underneath it all   
   (very carefully).   
      
   Here's Pandrol's patent, but I'm sure there are varying methods:   
   http://www.google.com/patents/EP1809810A1?cl=en   
      
   This guy doesn't say anything about shimming, but I don't see how   
   there wouldn't be any:   
   http://trackguy.com/railroad_track_contractor_assistance.htm   
      
   >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.   
      
   If you read the report, it doesn't say there's anything wrong with   
   ballast, but it's not done that way today. 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.   
      
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