Settlement Monitoring

Get a Leica NA-2 level and a GPM-3 Parallel Plate Micrometer.
Invar rods with legs.
Tempered steel meter scales.
Set realistic monitor points.
And get a copy of the Corps of Engineers manual (its on-line).

Or just do three wire and be careful.

As in all things in Surveying...it depends.

The main question is what is the expected rate and duration of movement?

After that is answered the rest is easy.

The most difficult part might be the establishment of a set of stable datum monuments in an area that won't be disturbed, yet close enough to the site that you won't lose all of your precision in making long ties.

You'll also need to establish discrete, repeatable monitoring points in the buildings, so you don't have to wonder if the elevation differences are due to settlement or inability to hit exactly the same point as the last time.

For instruments, I'd go with a geodetic-quality digital level and invar leveling rods. The proper procedures are very time consuming. How often would you have to monitor?

- Doug

I believe it needs to be daily monitoring, but haven't seen the specs yet.

Do you have a link to the Army Corps manual on this?

A couple of references:

Engineering and Design Geodetic and Control Surveying (EM 1110-1-1004)

Geodetic Leveling - NOAA Manual NOS NGS 3

(The Geodetic Leveling Manual is a 13.6 Mb pdf download.)

¿ 0.001' ? Seriously ? Please tell me you really meant 0.01' ?

CV

Howdy,

Here is a direct link to the
Deformation engineering manual at USACE site though you can easily find it from the other links provided.

I assume this is monitoring for changes in all three dimensions. As others have mentioned, detecting changes at the 0.001 foot accuracy level (2-or 3-sigma?) is unreasonable (unless it is a particle accelerator).

I recollect being asked to give a cost estimate for something similar. When presented the cost, the client demurred. We were looking forward to setting some of those nice UNAVCO deep drilled braced monuments ...

Modeling the data will be interesting as well.

Cheers,

DMM

Sure. Only do work you are qualified to perform.

I did something like that several years ago for the new Federal Building in Sacramento. The pile-driving had caused the sidewalks for a few surrounding blocks to actually subside to the point they separated from the buildings and we were doing QC/QA on the building construction itself so they asked us to go around to certain specified points on surrounding blocks to monitor further settlement. By that time, the damage was done and we never found any more settlement.

We didn't use any fancy equipment, just a good old Lietz level and standard Philly rod, but we used benchmarks a couple blocks away and took short enough shots, well-balanced for distance, that I could read (estimate) to the thousandths. After going around several blocks with a lot of turns, we never closed worse than about 3 thousandths and never found any of the TBM's to move outside that tolerance. It's really not that hard if you're careful.

BTW, maybe digital levels are the bomb now but the Topcon salesman was after me for years to buy one and I demo'd one on a long level loop that resulted in way crappier closure than I would expect with a standard level. He had all kinds of excuses about improper software setup and stuff and I said no thank you, I already have enough stuff that needs batteries and can screw up your data.

Kind of have to agree with Mike on this one. If you have to ask how to do it, then you probably shouldnt be doing it. If you are just asking for other methods, thats another thing.

.001 as others have said is unreasonable. My only suggestion is to make sure that your permanent bm's are in a place that is not going to move more than what your tolerances are, but close enough to your site.

Get yourself a digital level and invar rod.

I dont know about Topcon, but the digital levels we have used have been outstanding.

....001 as others have said is unreasonable....

Matt

We've monitored settlement to 0.001 inch. It simply depends on the application, equipment and procedure.


The more zeros in the tolerance, the more zeros in the invoice.:-)

Im not saying it cant be done. Just that it probably didnt apply to his situation.

We do alot of monitoring surveys, (not to your industrial level) and havent been asked to obtain that type of accuracy yet.

"0.001 inch" You're good man, I would have been impressed at 0.005+/- FEET!

CV

Corbin

If you think a digital level is expensive, try a laser tracker. Depending on the bells and whistles that you get, you can easily spend $150,000.00/unit. We own nine and have run as many as twelve in one day.

I would bet that discrete, identifiable, repeatable points on the buildings are VERY important.

It is typical for engineers (who nowadays take no survey courses as part of their Civil Engineering education) to OVER-SPECIFY the accuracy requirements. The Corps specifies ±2 mm for settlement monitoring of concrete structures. That is 0.006 feet. Much more realistic. Anything much less than that and it is difficult to separate out the noise from the signal.

You can buy bar code strips that can be affixed to walls of structures that can then be read by a digital level in passing. They make 2 types-a vinyl material that has adhesive on the back, and an invar strip that would have to be probably drilled in.

I have to admit I’ve never even seen a “Laser Tracker” but I imagine it would take something like that in a controlled environment to achieve any repeatable accuracy such as the elusive 0.001’. In what capacity do you use yours, some sort of industrial application?

CV

"It is typical for engineers (who nowadays take no survey courses as part of their Civil Engineering education) to OVER-SPECIFY the accuracy requirements...."

Well stated John. It has also lived on because it is difficult for a surveyor to educate a client when the client/surveyor relationship is on a commodity basis and not a value added consultative basis.

The spec of .001 feet is the spec, its not a typo. I realize that asking these questions may mean I shouldn't be doing it. This settlement monitoring is in addition to construction staking and I'm trying to figure out how to go about getting it done, whether in house or hiring someone else.

Isn't there non-surveying means of measuring building settlement? I have seen on other projects monitoring devices attached to walls that are all tied into a computer. Does anyone have information on these devices?

Thanks for all your input.

Do a search for inclinometers. We use them from time to time on bridges. Mostly to monitor scour of footings and resulting settlement. Some we've got are tied into phone system to send out alert during high stream flows if the footing begins to settle.
Not what you need them for, but they probably have an application that can work. Nice thing about them is they can determine when the settlement begins, as the measurement is continuous. Better to know immediately then waiting for the next level loop to be run.