Railway Survey Control Network

The same way I set up a Control Network for a Highway, Freeway, Canal, Water Line, Pipeline, Power Line, etc.

Keep the Primary Control well outside of the construction area.

Snug the Secondary Control up as close to the construction prism as you dare, but error on the outside as opposed to the inside. Secondary Control should have at least 1 (preferably 2 or more) intervisible lines to other Secondary (or Primary) Stations.

Tertiary Control is pretty much a temporary proposition, but should be tightly controlled by the Secondary Stations and protected as long as possible.

The extent to which GNSS and "Total Station/Robot" work is intertwined plays a big roll, not to mention the extent of LEVELING involved in the various Primary , Secondary, and Tertiary Networks.?ÿ

Loyal?ÿ?ÿ

Railway control is no different than tight control for anything else.

One consideration is locate control where itƒ??s needed, like in proximity of switches. ƒ??Point of frogƒ??. And make sure that the definition of curves is clear: degree of curve by chord or arc. Terminology can be confusing. And railway is very elevation sensitive. So I wouldnƒ??t rely on, or mix TS elevations with good 2nd order leveling. Leave a lot of reliable BMs for you and the construction crew.?ÿ

I would think the elevations are more critical than the horizontal, leveling for sure.?ÿ

If you're in the UK there are specific Network Rail standards you'll need to study.

@john-hamilton

Yeah they can shift a tenth L/R, they hate it, but not impossible. They can’t easily correct 1/10 up or down, that’s a bitch. 

@loyal

"LEVELING" - glad to see I'm not the only person left on earth that understands the importance of this component...

@larry-scott

Up is an easy correction, down is the hard one

@azweig

and they still back charge if they have to lift a several hundred ft to avoid a slope. And Iƒ??ve seen them try lower it, and youƒ??re right: very much harder?ÿ

?ÿ

@larry-scott

I work for a company that owns four Railroads. We are on-site when the contractors are doing the final lining of the track and check the track between each pass of the tamper.  If they are an 1/8 or 1/4 low, we usually tell them it's good. They can't guarantee that they wont be over on the next pass. We only run freight, so a 1/4 is not a big deal. 

@loyal

I've never done this specifically for railroad, but have done it for roads and highways. But if I did, this is how I'd roll.

I'm going to have primary control points about 1/4 to 1/2 mile back from the alignment and about every 3/4 to 1 mile along it, tied together by GPS, located in real good positions for the RTK base. Secondary control up against the construction limits, but clear, every 600-800 feet along both sides of the alignment, intervisible. Tied to the primary by GPS and to each other by traverse. The secondary control all levelled through by digital levels. The whole lot simultaneously adjusted, and a report prepared.

Mag nails and 60d spikes are not going to be satisfactory monuments for all this. Capped iron rods 24" to 36" long at least. Bronze plugs drilled into good concrete. MAGs, spikes, & hubs might do for the tertiary control.      

@azweig

to achieve or ensure 1/8-1/4 (inch) the surveyor has to twice as good. I worked a switch yard, container transfer facility, and they took no prisoners. So we made sure an 1/8 was in the extreme. If the track was off, but our control good, there was no argument. The contrary really hurts. 

@azweig

btw “1/10” is 0.1 ft.