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Vertical Bore Hole in Earth Dam

Vertical Bore Hole in Earth Dam

Vertical Bore Hole in Earth Dam

(OP)
Does anyone have an opinion on drilling bore holes in shorter (less than 40 feet tall) earth dams?  I have been told to avoid this practice at all costs as a hole in a dam is not a good thing!  I suppose drilling in a clay core is one issue but a vertical small diameter hole drilled off the crest properly (tamped) backfilled should not be an issue.  Getting past that, if holes are drilled, is there a preferred backfill method or material to use?  Thanks for any input.

RE: Vertical Bore Hole in Earth Dam

For dams of the that height, I would dry drill, i.e. do not use drilling fluid, and backfill with a cement/bentonite grout.

As the dam height increases or the dam material is soft, you run the risk of hydrofracturing the dam.  This can cause cracks to form and create problems, however, for a 40 foot dam I would generally not expect a problem.

The vertical hole is not really a problem.  Most larger dams have many, their called peizometers.

RE: Vertical Bore Hole in Earth Dam

This is a hot topic for dams of any size - to drill or not to drill.  Personally, I am of the opinion that drilling holes in the core is not a good idea, unless there are specific signs that point to a possible problem.  If you're seeing seeps on the downstream side, or you've got Piezo's showing you something, then its time to drill.  If everything is status quo, then I'd hesitate.

RE: Vertical Bore Hole in Earth Dam

flyfishgeo,

I haven't checked myself, but you could look through USACE and USBR publications on the web relating to dams.

Just a thought.

Jeff

Jeffrey T. Donville, PE
TTL Associates, Inc.
www.ttlassoc.com

RE: Vertical Bore Hole in Earth Dam

NO compressed air or foam!  They're much worse than water or mud, because of all the potential energy "stored" in the compressed air.  That could cause a fracture to propagate much farther.  The critical plane for fracturing is not horizontal; it's a vertical plane parallel to the axis, which generally has the lowest normal stress.

Some people like hollow-stem flight augers.  Some COE districts have lately been very interested in sonic drilling.

Gotta ask yourself how important the hole is.  How thick is the core and what's it made of - how easily could you fracture it?  What's on each side of the core - what are the consequences of fracturing it?  Is there a core?  Finally, as Dirty Harry said, "You gotta ask yourself, do you feel lucky?"

A hole has to be VERY important to be drilled through embankment core, especially if the core is thin.

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