Hollow Stem Auger in sand
Hollow Stem Auger in sand
(OP)
Will a hollow stem auger yield lower blow counts in F/M sand with trace silt below the water table? See attached typical boring log for site.
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Hollow Stem Auger in sand
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RE: Hollow Stem Auger in sand
RE: Hollow Stem Auger in sand
RE: Hollow Stem Auger in sand
Classify all this as "fugitive" information. The driller never documents these techniques and if you don't have a field geologist at the rig, you'll never know what went on out there, sigh . . .
f-d
¡papá gordo ain't no madre flaca!
RE: Hollow Stem Auger in sand
My question is: Could it be possible for the entire 2 feet of the sample be disturbed, yielding low counts? Blow counts above and below were higher in similar soil.
Thank you.
RE: Hollow Stem Auger in sand
I also echo the response of BigH and Fattdad - geo observations are very important; I also train geo's to communicate with the drillers as well to get driller comments. Often, if you have a good geotechnical driller, his information will be as valuable as the quantitative downhole tests.
RE: Hollow Stem Auger in sand
The problem is so common that I'd bet a lot of drilling firms don't even own a plug and don't have capability for water inside the stem. Their standard may be the quickest way.
So, when there are indications of low blow count possibly caused by the drilling methods, well the conservative approach then governs and you may be calling for piles when spread footings will do.
Of course one could go back and do some mud drilling and see if there is a difference when it is significant as to what the foundation will be.
Oh for the good old days with Gow drilling procedures. Gordon Fletcher of Raymond has turned over in his grave a lot by now.
RE: Hollow Stem Auger in sand
Now, do you have any sense of what the local geology is for this "running sand" formation? Often a regional context is what is needed to understand whether you are really in a loose, saturated sand layer or this is the result of drilling technique.
f-d
¡papá gordo ain't no madre flaca!
RE: Hollow Stem Auger in sand
I'm also surprised that he didn't sand his augers into the ground.
RE: Hollow Stem Auger in sand
RE: Hollow Stem Auger in sand
RE: Hollow Stem Auger in sand
As a former helper we always drilled with a plug while hollow stem augering. It solves a lot of problems and makes drilling easier and faster. I don't see how drilling without one is faster or easier. When drilling through waterbearing sand we always filled the augers with water before pulling the plug. It slows you down somewhat, but not dramatically. Heaving sands did occur periodically, but almost always mitigated or stopped altogether with water in the augers.
I agree with the statements above that drilling through waterbearing sands (especially heaving sand) should be done with mud rotary.
RE: Hollow Stem Auger in sand