A Harris, post: 374864, member: 81 wrote: The Mt Pleasant error is reported to be that the highway elevation and RR elevations were from two different sources.
They are still debating which one is right.
The obvious problem was that neither connected into the source information of the other to see if it would fit in the first place......
I had followed that story on the Tyler news when it was being discussed. The article you linked said 15" error. There is no way I would believe the railroad raised the rail by 15" just by replacing ties and tamping.
James
The thing about minimum design values is that whether it is determined by determining the minimum space needed for clearance (i.e. the "gnat's hair" minimum) or it is determined with a "minimum clearance to the largest expected thing", the designer is not going to exceed that minimum by any amount for any reason. So whether the standard was to have a minimum 3' clearance or 3mm clearance, the design would be exactly that and any error at any stage (initial survey, design, stake out, construction, whatever) would cause a problem.
It is like that line in the movie Office Space, "You know what, Stan, if you want me to wear 37 pieces of flair, like your pretty boy over there, Brian, why don't you just make the minimum 37 pieces of flair?"
No one really wants to do more than the minimum. I get that from my field crews asking, "Well, how many shots do you need for this?" I get it from the engineers that want to hire me to do topography saying, "Well, we only need like a dozen grades across this parking lot to do the design" and I get it from the contractor wanting me to stake a site, "Yeah, it will only take about 2 hours to stake that. There's only like 10 points I need."
And in every case, that "bare minimum" that these people talk about isn't enough to do things right.
Tommy Young, post: 374838, member: 703 wrote: One thing that drives me nuts is when an engineer designs something and tries to use every single gnats hair of space.
THIS
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Okay,
A majority of my business is for the railroads. We are just finishing up on a 16 year project redesign of a rail yard in Vancouver, WA. The original project control was based on NAVD88 but upon completion of the initial base mapping was complete the engineers requested we convert to NGVD29. Later down the road the State designed a built a substantial bridge over the yard. During constructions the railroads residential engineer discovered that 3 foot bust, about the difference in between the 2 datum, in the bridge design a big portion of the bridge was built. The railroad asked me to meet with the State surveyors and verify our work. After going through our control and verifying that our values were correct we tied into the State's control only to find that what was reported as NGVD29 was actually NAVD88. Fortunately for the State the bridge was 3 feet to high (I sure that cost a pretty penny) and only the underground utility crossings need to be re-designed.