Piezometers in a dam (foundation)

[kwon13]

Can anyone help me understand why to measure pore water pressure in foundation of a dam during operation ?

 

[DaveAtkins]

The piezometer indicates the groundwater level at that location in the dam. The information is used to draw a profile drawing showing the groundwater level upstream to downstream (known as the phreatic line). This information is used to design the various structural components of the dam for hydrostatic uplift pressure.

DaveAtkins

 

[SlideRuleEra]

...why to measure pore water pressure in foundation of a dam during operation ?

To indirectly measure seepage through the embankment. Change in pore pressure is important. Increased pore pressure indicates increased seepage. Increased seepage can cause instability which may progress to dam failure.

In 1983, we had a sudden, unexpected sizeable "leak" at our large hydroelectric reservoir earthen dam. Records of routine monitoring of pore pressure were stable. This indicated the leak was NOT occurring through the soil. We now knew to look for other causes.

(The "leak" was caused by rotting failure of long-forgotten wood stop-logs that had been installed 40+ years earlier to isolate a never-used industrial water supply penetration in the concrete power house. Water from the reservoir was gushing out through the underground open down-steam end of this penetration).

 

[GeoEnvGuy]

Multiple reasons as mentioned before seepage rates. Dam foundations on clay require time to drain excess pore pressure from when you build the dam or if you are continually raising the dam, this is a stability issue if a dam is raised to fast on a low permeable foundation.