Why we use N60? What is the meaning of this 60? 1

[Nafees29]

In Standard Penetration Test we are using N and N60. N60 is the corrected value of N. Why we are writing N60? What is the meaning of this 60?

 

[fattdad]

It's a reference to the typical efficiency of a safety hammer. If you have a 140 pound hammer falling 30 inches you can equate that to some dynamic force. But as it turns out only about 60 percent of that force actually gets to the sampler. If you are using a do-nut hammer it's more like 45 percent. If you are using an automatic hammer it's more like 90 percent. Normalizing the data to the safety hammer efficiency is one way to remove this variable.

Hope this helps.

f-d

¡papá gordo ain’t no madre flaca!

 

[BigH]

fattdad hit it on the head - some correlations use N55. Remember that most of the charts of "N" vs allowable bearing pressure or other properties that are older, say, than 1980s (and probably more like the 1990s) were generally based on the donut hammer and as a result be careful when correcting.