piezometer installation

[abih]

Hi folks

I am planning a geotechnical investigation plan consisting of SPT and piezometer boreholes. I wondered if I can re-use the SPT boreholes for piezometer installation. This way, I can save the budget of grouting these SPT boreholes. Please share your experience. Thanks.

 

[GeoPaveTraffic]

Yes you should be able to use the same borings for both purposes.

Mike Lambert

 

[Erdbau]

I would add that this is very normal to do.

 

[fattdad]

Here are a few things to consider:

Is the original boring on a sideslope where there is both a horizontal and vertical hydraulic gradient?
Is the formation layered with water bearing "sand" intervals separated by "clay?"
How deep below the water table is the original boring?

If you drill a boring that's 40 or 50 ft below the water table, if there is a vertical gradient and if the soils are layered, what piezometric level are you going to measure in the piezometer? Well, it'd be some average value.

You see if there is a vertical gradient in the boring, the piezometric level will be the average of the entire borehole. That means water will flow into the top of the piezometer and OUT of the bottom of the hole. You are creating a hydraulic pump. If there is any sense of contamination, you'll broadcast that from the top of the boring to the bottom.

I'm a fan of slotted intervals that are no longer than 5 ft. Now when I'm in the Coastal Plain and the topography is flat, sure I'd jam a pipe to the bottom of the hole, but only if the layering won't affect the results.

f-d

¡papá gordo ain’t no madre flaca!

 

[BigH]

Yes, you can use the same borehole as the SPTs. However, as pointed out by fattdad, you will need to have a plan of installation - where to place the piezometer (or standpipe), where to seal, are you installing more than one in a borehole (which I have done), etc.