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NONSTANDARD SPT RIG

NONSTANDARD SPT RIG

NONSTANDARD SPT RIG

(OP)
Dear colleges!  Here is the situation: due to lack of space we had to use small SPT rig with weight of hammer = 70 lbs., drop=15 in., same size spoon as for a standard rig. Theoretically the energy for smaller hammer is 4 times less, so to convert its N-values to standard ones, just divide it by 4. But here comes a problem. First at all, comparing two different borings about 50 feet apart (standard and lightweight rig) I found that stratas in two borings pretty much identical, but N-values for lightweight rig after dividing by four do not make any sense and in some stratas  are less than 1.
Secondly, after some research, I found that there is no direct correlation between these two N-values. There are too many other unknowns involved besides weight of hammer and its drop.
Any suggestions how can I do correlations?  Thanks for any help.
 

RE: NONSTANDARD SPT RIG

Don't have my copy at hand but Winterkorn and Fang (later only Fang) did have a chart regarding this I believe - section on investigations.

RE: NONSTANDARD SPT RIG

Foundation Engineering Handbook (Fang?) also has formulas for converting the drop height, weight, sampler diam. to SPT.

RE: NONSTANDARD SPT RIG

molerat2210 - I think that is what I said . . . but I could be wrong - I am getting old . . . . bigsmile

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