Building Monitoring Project

A few questions:

What horizontal tolerances are specified? (One parallel to the wall and one perpendicular to the wall.)
What vertical tolerance is specified?
What dynamic tolerance is specified?

What time frame will you be monitoring?
During tilt up to assure the panels are placed properly?
During construction and through the end of construction to verify the walls stay in the correct place?

> Any advice or suggestions will be welcomed. Thanks in advance.
The trick with this kind of job is not so much the targets but rather the control. Maintaining control on an active construction site is always a challenge. In this case you absolutely need it to survive or the whole monitoring campaign is compromised. You may need to reference the control to enable confirming that it has moved while the building remained stationary.

I agree with what Norman said. You must make sure the control is stable, otherwise you will not have valid data. Sometimes it needs to be set hierarchically, nearby points to monitor from, then other points set further away to check those points, etc.

Sometimes the best way to monitor a wall is by scanning it and comparing the scans. Or by putting paint marks at strategic locations and shooting them reflectorless or by angles from multiple setups.

In a sitaution like this I would plan the survey in the office, and run the data through a least squares simulation to see if the desired accuracy is being achieved.

I use Geolab for least squares, which makes it easy to do simulations. I imagine Star*Net and others have a similar capability.

I agree & disagree. You need to maintain control, but the control does not need to be occupiable. If you can establish 5 or more stable points that you can observe, you can do a 5 (or more) point resection at any convenient point anytime you go out. The trick is getting good positioning on the remote points. Once you do that you will be amazed at how good you can get a current position on your instrument and follow on with good positioning on your points to monitor.

> I agree & disagree.
I think we just agree. If it is possible to set permanent, stable control that can simply be occupied then that is preferable. But if it just can't be done, the method you describe is valid.

Occupying control is less accurate than resection.

With monitoring when using resections you still want to set up near the same area, though, if using reflectorless. Beam spread from different locations will yield slightly different positions.

We usually set up over a PK with no constrained value (used it as a check later) tried to get near the same HI and resected to points on top of buildings surrounding the site.

The one sigma reported by survey controller (never trust it, though) was always around .001' in the field.

TBC usually verified. Once in a while it would creep up to .005'.

Turning that many angles using Trimble robotics requires a real good set of legs, though, if going to be set up for an hour+.

Do you have the Monitoring option in Trimble access? I think you will find it worthwhile.

Solid control points are a good idea - are you able to set up a couple of pillars to work from?

Well thanks for all the replies! This project should be an interesting one. I am still working out the specifics for the tolerances, but for this site the multiple points and resections will be the best approach, otherwise it will have a pretty short baseline.

We currently don't run Access; still have Survey Controller, but I will look into the Access Monitoring. Perhaps the cost of the upgrade can be passed along..

Thanks guys and have a a good day out there.

Jim, I'm curious - what does the Monitoring module offer to the average project?
I would normally just use stake points routine. (S6 and TSC3 running Access)
You can load up a whole list and it will auto turn to them in 3D. After centring the cross-hairs (if not auto-lock) then "accept" stores the point. A stakeout report can be generated with deviations that can be copied into excel. The deviation is also displayed at the time of measurement as well.

I imagined that the monitoring module is for automated setups where the instrument will be checking the backsight and the targets at regular intervals and sending alerts at certain deviation limits. Maybe also generating graphs of deviation over time?

For monitoring vertical movement with total station you will want to be setting up either by free-station/resection or if setting-up over a point then by also using remoteBM/remote height transfer.
Instrument height measurement errors will get you otherwise.

I do a bit of monitoring work using retro targets. Bolt on monitoring prisms are better it's just the expense. If you need to do a lot (we regularly have 80-100) the cheapest way to mount a prism is probably by buying cheap peanut prisms from china on ebay and gluing them on with grab adhesive. Not sure what you call the glue over there. There are a few brands here like Gripfill, No more Nails.
Alternatively some of the monitoring prisms are not too bad a price if you can get them back and re-use them.
I nearly always end up with retro targets because that is what the client is used to using and is willing to pay for.

My limited knowledge of tilt-up construction tells me that you will have to attach the targets to the walls after they are lifted up (access by cherry picker?). In theory I suppose you could cast them into the walls but they would have got covered in grout so you would need to go up and find them/clean them anyway.
Another problem could be obstruction if they are putting up scaffolds or anything similar. Will the walls be painted?

"was always around .001' in the field. TBC usually verified. Once in a while it would creep up to .005'"

What total station, tripod and targeting systems are you using?

The building it complete and occupied. It is cracking in the floors and walls. There are already crack monitoring systems in place.

It does work pretty much as you imagine

With the Access Monitoring software you provide it with a
The occupied point
One or more backsight points
The points to be observed - including target height and prism constants

You then set up a schedule - for example one round every 15 minutes

It then observes each point automatically and repeats and repeats and repeats

It will generate an alert if a point is measured to be beyond a certain tolerance from the original position.

You can specify if the target is to be measured automatically or manually - this is needed as Trimble's autolock has a maximum distance and does not always work if the target is dirty.

There is a facility for temperature and pressure correction, options for the number of faces, order of obs etc

There are a number of reports available and exports to CSV file. At the end of each day we grab the raw observations and the target positions. You can get displacements etc. I dont think it does any graphs

The software is not perfect - the user interface could be improved, and every now and then it crashes and needs to be restarted - but it doesn't loose data and is easy to get back to where you were. Recently our TSC3 was in for service and the loan unit had a slightly newer version which appeared to be a little more stable

At the moment I'm using it to monitor a piling project for rebuilding a wharf damaged (or more destroyed) by our recent earthquakes.

That's interesting. Can it be set to check the backsight(s) on each round? I would have thought so.
What are the options for alerts? My TSC3 has a SIM card in it so should be able to send an SMS in theory. I imagine it will be through Trimble's "connected community" though? What about email?

I do offer the automated monitoring option to clients occasionally where appropriate so it would be good to know whether this software module alone would do it or whether I would need a laptop connected.

Are you checking the adjacent buildings aren't affected by the piling vibrations?
How's the rebuild going? Still may more years to go? Some friends of mine are planning to emigrate this year. She works in construction so they are looking at Christchurch.
I was there many years ago and I loved it. Maybe I will be back one day, assuming the government will have me.

Yes it checks the backsights every round

Have not seen an option for email or sms alerts in our version of the software - I'll be using it again in a couple of hours and will dig around a bit and let you know

We dont have any nearby buildings - they are more worried that the existing seawall might collapse.

The rebuild is slow and getting slower - the central city has become mired down in politics - there are still huge fights with the insurance companies - the private money is leaving town.

If your friend wants a construction job she should be here now - not in a year's time. Yesterday one of our crew resigned - do you want a job?

I think the email/SMS alerts might be generated on their "4D" software product.

Yes I've been telling them to get going for a while now, they have young kids and not too happy with the area (or country!) they are going to be bringing them up in. I think they are finally going to do it within the next few months.

You position is certainly a very tempting offer! I will be thinking about it often but I don't think I can do anything like that in the next year or two so will have to take my chances what might happen after then.
You never know though, maybe I'll suddenly email you one day for advice (if that's ok).

We got similar results (.002 to .003 typically) using a Topcon 3003 reflectorless to tape targets mounted on walls. We set the square tape targets "diamond" orientation and didn't site with the center of the cross hairs, but rather centered the vertical cross hair on the bottom of the diamond and the left cross hair on the left side of the diamond.

We were working with another surveyor on this project who had experience in this manner. Quite frankly I was skeptical of the results the first few times, but when we kept getting the same type of results time after time I became a believer.

This is a MAJOR problem within the profession. So many "Professionals" profess accuracies beyond the capability of the TS.

here is the info for the 3003
Measurement Accuracy
Non-prism Mode (Diffusing Surface)
1.5 to 2.5m(5 to 82 ft.) ±(10mm)m.s.e.
25m or more (82 ft. or more) ±(5mm)m.s.e.
Prism Mode ±(3mm+2ppm × D)m.s.e. D:Measuring distance (mm)

http://www.topcon.com.sg/survey/gpt30.html

I agree - that's why I was skeptical to begin with. But as we got into the project the results were repeatable to accuracies much better than I expected. And the partner on the project was using a different gun and getting similar, repeatable numbers. I am convinced that if there was movement we would have detected it.