Inclinometer data interpretation

[geotekken]

Are there any good publications/papers on how to interpret inclinometer data?

Specifically, I am trying to find some sort of rule of thumb that would let me know when a slide may be occuring. We are installing an inclinometer in a dam that has had some localized slope failures.

What I'm looking for is something to the effect of 1)When inclinometer top moves more than ___ inches per week 2) When inclinometer appears to be rotating at (X) degrees per week- I am just looking for something to give to the field techs/EIT's interpreting the data to have in the back of their mind as sort of a check.

 

[ishvaaag]

http://www.geomechanics.com/pdf/apps/DamMonitoringWithTiltmeters_L00225A.pdf

http://www.geomechanics.com/dspapp.cfm?appid=73

This very nice link appeared just under your question when I read it. Hope it helps.

 

[GeoPaveTraffic]

goetekken,

There is no one "rule" to indicate when inclinometer data indicates that a slide is occuring. As with much where geotechnical engineerin is concerned - it depends. It depends on the quality of the inclinomeeter readings, the quality of the inclinometer installation, the type of slide, how well defined the slide plane, and many many other factors.

The way I always do it is to plot the data and look at it. The human brain is wonderful at spotting patterns of movement. Also, not that if the inclinometer is on or near the back slope of the slide, it is not uncommon to see two or more areas of movement at very different depths.

Good luck.

 

[InDepth]

It would also be good to perform some analysis to determine "expected" slipe planes and where they intersect the inclinometer. i.e. focus attention to certain areas in the data where there is a high probability of slip.

Also, performing an initial analysis will allow you to determine how deep you need to place the inclinometer.

One other item you need to look into is when will the inclinometer lock up. Depending on the size of the inclinometer it has a limit. From what I remember on slides, you will see a definate kink/point of rotation in the data when slip has occurred or is initiating.

You should look at the slope indicator website, or call them up and ask about their experience.

Do you have any mitigation plans in place?

 

[dgillette]

Geotekken - When you say "inclinometer," are you referring to the sort that sits fixed in the ground measuring changes in inclination, or the sort that is lowered down a casing and used to produce a profile of displacement from inclination measurements every two feet?

Try to get ahold of the Bureau of Reclamation's Embankment Dam Instrumentation Manual. I have it as a .pdf, but it's 35M and I don't know if it will upload, or if you'll have to get it from them directly.

You're seeing slope failures of the dam embankment?? This must be a heck of a dam. I hope you are draining it.

 

[ishvaaag]

http://www.naun.org/journals/geology/ijgeo-10.pdf

This article has a table on how rate of movements relates to risks. I think to have seen the same or alike somewhere else but don't remember where.

 

[geotekken]

Thanks for the help all. The inclinometer data I have such far suggests relatively small movement, so thus far I have nothing to be concerned with. The net displacement is on the order of .006 inches over 6 months.

It's kind of a smaller dam (for a storage pond, actually). Fortunately, we have not seen any tension cracks at the surface- just some surface sloughs. I will keep you posted.

 

[GeoPaveTraffic]

0.006 inches over 6 months! Unless your data looks perfect, i.e. you have multiple sets of readings and they show a steady progression of movement; I would say you have NO movement of the structure.

Inclinometer readings must always be compared to each other and the pattern as well as the magnitude of the movements considered. In general, any movement less than 0.25 inches in my book is always suspect unless supported by multiple readings.

 

[Dirtguy4587]

As far as I know, conventional slope inclinometers only have an accuracy of 1mm. I use 4mm as my "movement" criteria (just a bit less than GeoPave's criteria). Also, depending on the structure, acceleration is as important as movement. Stress changes will cause strain, and detection of movement would be expected. My alarm bells go off if I see a)the movement is happeneing within a distinct zone, b)significant movement is detected (multiple readings >4mm), c)rate of movement increases.

 

[GeoPracRockman]

The Transportation Research Board has a nice document for inclinometer use. It contains a short section on data analysis and presentation, including a discussion of typical accuracies and common error types.

http://pubsindex.trb.org/document/view/default.asp?lbid=872704

Transportation Research Circular E-C129 (October 2008)
Use of Inclinometers for Geotechnical Instrumentation on Transportation Projects: State of the Practice

Rockman (Randy Post)
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