Hollow Stem Auger versus Mud Rotary (Beach Sand) 4

[NBRY1]

When should Hollow Stem Auger (HSA)/Standard Penetration Test (SPT) borings not be utilized?
Recently, I was provided soil test borings (logs) performed a few hundred yards from the beach and HSA/SPT was performed. Groundwater was at 4-ft in SP classified sands. The N-values did not appear unreasonable, however, I would think Mud Rotary would be preferred. Just looking for clear guidance on whether HSA/Split Spoon techniques in this type of environment is considered reasonable......as obviously, it
can be done.

 

[fattdad]

We wouldn't use HSA drilling for much deeper than 5 or 10 ft below the water table. It's all about controlling heaving (saturated) sand. Our drillers must be able to convert to mud if they get heave that they can't control within one sample. We'd require a field geologist or engineer be on hand to document such matters. Typically; however, we'd just use mud in the Coastal Plain.

Clearly there are two problems: Heave from gradient and heave from auger movement. A 2-1/4-in HSA has a 6-1/4-in outside diameter. Each time you break the augers, they drop - even when using the auger fork. A 1-in drop can (mathematically) cause multiple inches of heave. Both problems are addressed in mud rotary.

f-d

ípapß gordo ainÆt no madre flaca!

 

[Ron]

Agree with f-d.... mud in coastal plains

 

[GeoEnvGuy]

Agree with fatdad preferred method for liquefaction assessment of saturated loose sands.