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Wednesday, February 27, 2013

Transportation Defined: Inclinometers

An inclinometer measures slope
inclination at a specific location.
If you've been following our US 89 updates on Facebook, YouTube or the US 89 Web page, you know that we have been talking a lot about geotechnical engineers lately. Today, we want to take a look at one of the tools they work with: inclinometers.

Stay tuned to the blog to find out how geotechnical engineers are using inclinometers to assess the site at US 89.

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When engineers suspect a slope or embankment might be moving, they can use an inclinometer to see if their hunch is correct…

But, what’s an inclinometer?
An inclinometer is a device that measures the slope inclination (movement) at a specific location.

ADOT Geotechnical Operations Manager J. J. Liu explains that an inclinometer consists of a precision-tooled plastic casing (it looks basically like PVC pipe) that has internal grooves carved out of it.

That casing is installed into the ground through a vertically drilled hole.

Next, the casing is weakly grouted into place, allowing it to shift with the ground when (or if) it moves. A probe (not just any probe – this one measures tilt and can calculate the magnitude, direction and scope of any ground movement) is then inserted into the casing in order to measure the inclination at various points along the length of the casing.

“The inclination data is compiled and compared with a baseline reading, which we obtain right after the inclinometer is installed,” Liu says. “The difference at each elevation is the magnitude and direction of the movement at that elevation.”

We mentioned the internal grooves above and we don’t want to forget about those…

Inclinometers out in the field.
The grooves are on the inside of the casing and serve as a kind of track for the inclinometer probe (the probe has guiding wheels – did we mention that? You can see them in the photo above).

So, the wheels sit in the grooves and measurements of the inclinations at various points are taken by the unit as the probe is pulled up from the bottom of the casing.

Hopefully this is making sense, but if not, try to picture a big milkshake (it can be any flavor!).

We’ll say it’s a very thick milkshake … thick enough that you can drill a hole through the ice cream, all the way down to the bottom of your glass. Now imagine sticking a big straw down that hole that you’ve just drilled out.

The straw is kind of like the casing that we described above. If the milkshake moves or shifts a little bit, the straw is going to move along with it.

There’s no real food analogy to go with this next part, so we’ll just say that you’ll place a probe (that same sophisticated probe we described earlier – the one with the wheels that can calculate the scope and direction of any movement) down the hole of the straw…

You’ll use the probe to take periodic readings and, over a period of time, you’ll know how much your shake is shifting.

Transportation Defined is a series of explanatory blog posts designed to define the things you see on your everyday commute. Let us know if there's something you'd like to see explained ... leave a comment here on the blog or over on our Facebook page!
Posted by Angela DeWelles   |  Labels:  Inclinometers, Transportation_Defined, US-89
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