The railroad wants us to monitor the tracks while construction takes place in replacing a railroad bridge and its abutments.
They are going to replace half of the bridge and abutments at a time so two of the four tracks are out of service. So we need to monitor the two tracks that are still in service while they replace the other two
The tracks are on ballast made up of rocks....lots of it.
The specs from the engineer (CDOT) require us to drive a 30" #5 rebar, into the ballast in between the rails, and put a cap on it.
We set rebars every 15' up and down the tracks in the construction area, then every 25' for 100' outside the work area. We then shoot each rebar, once a day for movement.
I am a little puzzled why we aren't monitoring the rail itself. Wouldn't that make more sense?..the rebar is 30" into the ballast while the rr tie is maybe 6" into the ballast. I'd think the rail would move before the rebar would...
Anybody else ever monitor Railroad tracks for movement? Or for monitor anything else for movement?
You are required to measure to the gauge from your center line points, right? Otherwise I don't know how your going to monitor the tracks.
Is it on a curve? How fast is the train. A fast and heavy train on a curve will flatten the curve out on new ballast pretty quick.
The procedure you described would allow you to possibly[/i monitor the movement of the bed of the rail or the embankment under the bed. It would not give you any reliable indication of the movement of the rail.
Is there going to be excavation adjacent to the area where the monitoring is being done??
Very Bizarre
Why monitor a point that may move independently of the movement induced in the object intended to be monitored?
A rebar may move because of small scale local settlements.
A rail is spread over a gretaer dimension and will not settle in a small area due, to say, a sinkhole of only sevral feet.
NEVER had to perform monitoring like that, and monitoring is my bread and butter.
Has he never established a monitoring program?
Certainly deserves a few questions.
The specs are from the engineer. Explains a lot. Are you checking vertical? horizontal? Your control needs to be out of the area of disturbance; preferrably in a cut on original ground. BTW, deer will gnaw on plastic caps. Speaking from experience.
Yes Brian there is going to be excavation. there are four tracks....two of which will be replaced, along with half the bridge, while the other two are in service.
I'll get some photo's to post.
We are checking horizontal and vertical.
Very Bizarre
Scott,
I have no idea about the engineer...all I know is that its from the engineers from metro-north and cdot..btw its the New Haven Line, in Southport, CT.
I'll try and get some photo's...
I asked questions, similar to the ones I posted, but got nowhere.
Obviously its (engineering) is outside my area of expertise, but I'd thought I'd ask here..
One possibility would be to use a scanner to scan the rail.
Another would be to put paint dots on the side of the rail, and shoot reflectorless from a spot away from the work.
I can see why the engineer wants to monitor the balast, but I would suggest that they install some Smart Targets on the rails and monitor the rail, unless you can sell them on scanning it. Here is a link to the berntsen smart target.
First off, one has to consider that the rails, ties and ballast all move EVERY TIME a train passes. Just watch the ties move up and down as each wheel carriage passes over. Generally, for the short term, in the vertical, the rails settle back into the same position. Horizontally, if it is a straightaway, the same should be true, but on curves (especially high speed lines) there may be gradual displacement.
From your description, it sounds as if they expect the ballast to be undermined from below, therefore settling and affecting the ties and rails. But I doubt that only a 30" rod would be effective. The ballast gets a lot of vibration and might cause the rod to start to wiggle out.
1. Most effective would be to monitor the actual rails. It shouldn't be too hard to create some painted or scribed targets on the web for H & V shots. For vertical, I'd prefer to just shoot top of rail.
2. Failing that, PK's in the ties. It's pretty much a given if the rails are moving, the ties are moving, and vice versa.
If you are monitoring a bridge, seems to me the things to be monitoring would be the soldier piles or sheet piles next to the remaining half of the abutment remaining half of the abutment....after all isn't that what's holding up the tracks?
If that's moving, it's the key to the success of the whole project, no?
should you be thinking about thermal expansion and contraction as well. the other posters, above, have made good points.
there is a hand pushed "car" that rides the rails. sorry, forgot who makes it.it is portable/folding, etc. you can put a receiver on it with tilt sensors and do the monitoring on a kinematic track, or possibly put a prism on it and get edm data.
cheaper and more practical is what i made back in the day. basically a bent metal bracket that clips to one side of the rail, over the top, and back down to rest on the bottom flange. drill a hole in the bend so that the prism pole can rest on the track at the gauge's edge. the whole thing can be made easily with a rebar bender or two vise grips. drop me an email if you need a sketch
