Settlement Monitoring

[PE_PLS]

Does anyone have recommendations for monitoring building settlement, accurate to the 0.001 of a foot?

I am working on a project where we need to monitor settlement for 20 separate buildings adjacent to the construction.

Any ideas will be appreciated.

Also, we would be willing to do contract work with an appropriately experienced PLS in this field. Private message me you would be interested.

The location of the job is in the North SF Bay Area.

[cbainum]

.001' sounds pretty harsh, could your spec be .001m or 1mm?

I can share with you our deformation technique and our obtainable accuracies, if you like.

You may also want to look at the high-rise monitoring that the USGS is doing with GPS, but that may not fit your .001 tolerance.

[Ben Lund]

Dylan,
I have a project where we are doing the same thing. After talking directly with the geotech, he lowered the spec to 1/4" or .02 feet. The geotech said that he wrote the spec based on a guess as to what he would need and had no idea what type of precision modern survey equipment and procedures provide.

[LS_8750]

Yeah, that 0.001' sounds wrong. I would check with your structural and geotech and have them confirm and agree to the appropriate level of accuracy. It will depend on the adjacent building construction type, the use of the adjacent buildings, the type of shoring they plan to use, and the type of soil or geology the buildings are constructed on. Think vibration and glass.... You could equip adjacent buildings with vibration monitors if need be.

Last year we did some settlement monitoring at the Santa Cruz Beach Boardwalk on a couple adjacent reinforced cmu buildings while they were driving piles. We were on beach sand right next to the railroad tracks and about a hundred feet from the 100 year old roller coaster.

We just set hard nails in the sides of the buildings and did level loops through them and to an off site benchmark. We ran a few at separate times prior to construction to establish our basis and to see if there may be some noticable tidal influence. Then when the pile drivers started we ran about one every hour. We closed our loops within 0.005 ft. and checked our data for any trends that may be developing.

At the same time we took horizontal shots on the nails to see if there might be any lateral building movement.

It was all pretty boring stuff except for the occasional lense calibration on various creatures on the beach...... Except for when the shoring started to fail. Then we got busy...... But all in all we recorded 3/8" settlement on the nearest adjacent building. The SE was ok with it.

[pls7809]

Come up with some crazy number to monitor to that level, of course after you research methods for yourself or sub to someone who can do it who gives you a realistic price. Maybe they'll pay it, maybe they'll have a heart attack and say, well we can live with 0.02'.

[Ian Wilson]

The tolerance can be met. The budget likely isn't there to meet the tolerance, but it can be met.

The sad thing about this requirement is that a "low baller" will simply take a wing-ding single shot to the settlement point from a control point 1200' away using a 10 second gun in 95º weather without ever measure temperature, elevation of humidity. The PPMs have probably never been adjusted since the gun was bought - second hand - without any service or calibration in the past 5 years.

The display will list the elevation to as many as 5 decimal places.

This guy will issue a "report" listing the elevations to at least 3 decimal places.

Even sadder is the fact that no one at the agency of even the surveyor who "wins" this project will ever know how useless the data really is. The agency will have been ridiculously overcharged for a bad survey instead of paying at least twice as much for a reliable survey from someone who actually understands how to achieve such accuracies.

[LS_8750]

Agreed Ian.
Being an engineer as well, I think now is the time for the surveyor to question the precision requirement, because as you said it will greatly affect the scope of work.


Cheers!