This week’s blog is Part 2 of our instrumentation series. Piezometers and inclinometers are two types of internal instruments used to measure a dam’s movements. Both of these instruments will be installed in the new Calaveras dam.
Piezometers
A piezometer is an instrument that monitors the ground water through the dam’s core and into the downstream drainage blanket and downstream rock/soil shell. A piezometer helps to ensure that the ground water surface does not erode the toe of the dam (the bottom downstream part of the dam). It also helps track the water level in the underline bedrock foundation.
Image courtesy of http://www.briodydrilling.ie/services-monitoring.asp
An open stand-pipe piezometer is an open pipe (see picture above) that permits water to enter. The water level is measured and compared to other piezometers surrounding the dam’s face. These types of piezometers are called open-stand piezometers. We also have automated piezometers called Vibrating Wire Piezometers (VWP’s). VWP’s are data collection devices. We will have a total of 17 VWP’s and 14 open-stand pipe piezometers at Calaveras Dam.
Image curteosy of http://www.slopeindicator.com
Inclinometers
An inclinometer is an instrument that measures the movement of a slope with respect to gravity. Slopes on dams are built to be stable but still need to be monitored for possible movements. Inclinometers verify the stability of dams, dam abutments (sides) and upstream slopes during and after a reservoir filling.
How Inclinometers Work
Inclinometers measure the orientation angle of an object with respect to the force of gravity. This is done by means of an accelerometer, which monitors the effect of gravity on a tiny mass suspended in an elastic support structure. When the device tilts, this mass will move slightly, causing a change of electrical charge between the mass and the supporting structure. The tilt angle is calculated from the measured electrical charge. You will always find inclinometers in pairs or sometimes in 3’s. Two inclinometers placed at Calaveras Dam.
Piezometers and inclinometers will play an important role in Calaveras. Once they are placed, they will need to be monitored and observed on a frequent basis.
See you around the valley!
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