Best Piezometer to be installed on a dam 5

[pelelo]

Does anyone has any idea of what would be the best recommended piezometer to be installed on a dam?

Among the Neumatic, electric and stand pipe each of them have their advantages and disadvantages.

I have read that the neumatic could be the best one to be used a long term.

Please advise.

 

[GeoPaveTraffic]

I prefer vibrating wire piezometers to pneumatic. Pneumatic can be very temperamental, especially if you get any air in the system.

Open stand pipe are fine in course grained materials. In fine grained materials, open stand pipes tend to response very slowly to changes in pressure due to the volume of water that has to flow. You also have to be careful with the length of sand pack/screen since the pipe can allow water to flow from one layer to another.

I would not use electrically resistance strain gauge piezometers in a dam under any conditions since they tend not to be stable over the long term.

Mike Lambert

 

[pelelo]

Thanks GeoPavetraffic,

Adding to your comments: The stand pipe is also not effective when dealing with cold weather as water freezes in the pipe.

 

[geomane]

Many of the US Army Corps of Engineers dams in the southeast contain open pipe type piezometers. Much of the instrumentation on their projects are actually open pipe type: uplift cells, pore pressure cells etc. That has a lot to do with when the dams were constructed though. They are slowly starting to replace the old open pipe pz’s with vibrating wire type.

Some issues with the open pipe type pz are issues with surface water getting into the instrument, slow response to pore pressure (as GeoPaveTraffic mentioned), manual readings are required and personnel taking readings can make mistakes (human error). Never had issues with the water freezing in the instrument. I think lightning can be an issue with vibrating wire pz and the data acquisition system. You also have to worry about debris destroying the wiring for the vibrating wire pz if it is located near a spillway (uplift cell scenario).

I personally like the vibrating wire pz.

 

[geomane]

Open pipe type pz’s also have issues with biofouling. So you will have to keep them clean. Which can be a major pain in the butt.

 

[fattdad]

short screen lengths! As it less than 2 ft! Make the screen length too long and you'll record an average over the screen interval. If there are higher heads at the top of the screen and lesser heads at the bottom of the screen you'll also set up a pump within the well. Just limit your screen length!

f-d

ípapß gordo ainÆt no madre flaca!

 

[Okiryu]

Suggest to take a look at this book:

Geotechnical Instrumentation for Monitoring Field Performance by John Dunnicliff.

Although I have not implemented instrumentation for most of my projects, this was the textbook for my geotech instrumentation graduate course. It is very good.

 

[aeoliantexan]

If rapid response is needed or you want automatic recording and/or transmission, vibrating wire piezometers are a good choice. If not, I prefer open standpipes because they can be checked using falling head tests, serviced by surging and flushing, and may have a longer life. A vibrating wire transducer can be hung in the standpipe for automation or remote reading.

30 to 50 years ago, most open standpipes had galvanized steel risers, which have suffered a lot from corrosion. In particular, risers that begin in soil and then pass through a concrete structure tend to rust through just below the concrete. I have not seen much problem with PVC risers unless the embankment underwent substantial settlement.

Freezing should not occur below the frost line. If the water level is within the frost zone or above the ground surface, insulation is necessary. Some have used a layer of non-freezing immiscible fluid on top of the water, but I have not tried it.

I was a fan of pneumatic instruments some years ago, but I think the VWPs are a better choice nowadays unless you have an unusual situation.

All types are capable of failure or unreasonable results. Be skeptical.