Vibrating wire piezometers in bedrock

[harpoon]

Hi

I am involved in a geotechnical investigation for a Lock in Ontario. The Lock floor slab is in poor shape due to a combination of poor concrete and unbalanced hydrostatic pressure of about 10 to 20 feet on the Lock floor when the Lock is dewatered. The Lock slab is supported on bedrock (shale: RQD of top 5 feet varies from 0 to 50%). We are leaning towards anchoring a rehabiliated floor slab into the bedrock to prevent uplift due to hydrostatic pressure however we need to get a handle on the hydrostatic pressure below the slab.

I am leaning towards installing vibrating wire peizometers in the Lock floor and monitoring them over a dewatering cycle to establish pressures. Is there any experience with this? How do we route the cables so that they are not damaged? Is wireless monitoring feasible. The Lock will have 50 to 60 feet of water during normal operations.

Thanks in advance for any inputs.

 

[GeoPaveTraffic]

It has been done, U.S. Army Corps of Engineers has piezos on many of their locks. As for how to do it, the devil is in the details.

If your firm does not have extensive experience with instrumentation, I suggest you find a specialty firm that has that experience to work out those details. I know of a couple in the States, but none that are based in Canada.

As for wireless; none are available that I would recommend for this application.

 

[mudman54]

how are you installing the piezometer? is the lock dewatered when you install? two issues seem to be
1. getting data for design of the construction
2. getting data for evaluating long term performance

once you get the cables for the vibrating wire piezometer installed, protect them in conduit back to a logger box. from there you can send some of the data wireless, such as when water levels reach an alarm level. as i understand it, the alert is transmitted by a cell phone call. perhaps the actual water level readings can be transmitted; talk to geocomp, they know how.

 

[aeoliantexan]

Solinst and In-Situ both make self-contained piezometer-dataloggers called Leveloggers or Trolls. They cost a few hundred dollars. You could install a conventional standpipe observation well through the floor, grout around it, and use a threaded cap. You can place the device in the pipe and cap it. Come back later, remove the device and download the data. You may want to install one in the water just above the floor to record the water level history in the lock chamber. No conduit or cables needed.