Slope Monitoring

I've done monitoring on slopes before...never with RTK. Always did it conventionally or with a robot. I wouldn't think you'd get very good sat geometry on a hill of that size, but I'm unaware of your location. The rebars should be pretty long--if shifting happens, you'll start to see them tilt over to almost unusable. Make sure they are sticking out of the ground a half foot or more.

#1 Scan the Slope. If you do not have a scanner, sub that to a trusted surveyor.

#2 Set a Grid of permanent markers that you can locate from 2 or more very STABLE control monuments. Berntsen has some reasonably priced targets. A short sign post might work well to mount these targets. Remember that you do not want your monument to be more stable than the slope. Driving it 2 feet deep and leaving 1 foot exposed might be better than driving it 4 feet deep.

#3 Take your Total Station to a Calibration Baseline and check it out. If it has not been dealer serviced in the last 9 months, send it in for its annual checkup.

#4 Use your Least Squares Package to make a test run and see if your equipment is capable of getting the results required.

#5 From your STABLE control monuments tie all of the monitoring points from 2 or more locations. Rune your measurements through Least Squares and ensure that you have meet the tolerances. Remember to collect lots of meta data. You will need to correct for temperature and pressure, so check your thermometer and barometer.

#6 Come back at the required interval and repeat your measurements. If you detect movement, suggest to the client that the slope be scanned a second time.

Remember, if you do not have the equipment to meet the specifications you might want to pass on the job, or become a broker and pass the job on to someone with the equipment and expertise. There are several people that post on this board that have done this type of work. This is good work, but the liability could be very high.

The order that I have the steps listed in probably needs to be changed.

Thanks for the good advice.
We have several Trimble S6's, so I think we'll go the robot route on this one. Scanning the hill would be the best method, but is not an option (for a variety of reasons).

This project is in a very rural area, and I think the client is looking for significant movement- feet, not millimeters. Nonetheless, you made some good recommendations...much obliged.

There was a post about monitoring a while back. Make sure that your control is in solid ground. I've also used reflector strip targets set in solid objects to resect myself in with good results. This rules out some set-up error. If you could set reflector tape on the slope, that would be even better.

My take is that the less calcs and massaging of the numbers (measurements) the better. With lots of experience with monitoring and even expert witness on it, I have taken over projects from surveyors who were doing what you are thinking of doing.

Suggestion: Monument three straight lines across the slope with one being 100' from the bottom, second being up 200' from there and a third being 100' from the top of the slope. Set two monuments outside the slope area at the end of each line (and on the line) for control.

Check: Run a control check and if OK, start checking your monitoring points. Set up on one end and record how much each monument is off the line and the elevation. Do all three lines. No Calcs. Input to spreadsheet. Add to report.

No explaining the measurement variables of your equipment or the atmosphere or the lack of a plumb rod, etc. etc. Heck, land owners can understand this and so can engineers and even attorneys can understand it! Amazing.

Now go do it the way you want to....

Any thought about slope cover.
Is it grass? Weeds?
Will it be mown or will it grow four feet tall?
What does that mean to exposed rebar.

DO NOT USE RTK, not going to be precise enough. You'll see way to much "flutter" in your results and not know if it is truely moving or not. Your best bet is a robot, with solid control off site, closed loops. And make sure you code your points logically. Set up a spreadsheet to dump your coordinates into and report the results.

What type of slope is it? Cut or Fill? You may want to set a mix of long and short rebars, what if the top 6-12" of the slope move, but the 48" rebars do not move because they are in solid ground below and the top 6-12" moves around the rebars?

how long are you going to be monitoring? a few weeks, a month, a year?

We have had success with Trimble S6 and its face scan command. Set permanent control point with good repeatable backsight. 1st check you establish Lower left corner of scan area, upper left of scan area and a point on right edge. Pick scan grid and let it go. Last check we did about 800 points on 5'x5' grid in about 30 minutes. Compare scan points between visits in Excel spread sheet. On trouble points you can stake out and look through scope to detect interference (gras, leaves, etc). One problem with your scenario is size of area being approx. 600 ft vertically. Probalby could travese between setup points and use some type of overlap. Ours is about 150' wide x 250' vertically and control point is elevated approx. 50 feet and about 150 feet from face of slope/cliff.

Good luck.