Split-spoon sampling

[ladypersia]

Hi, I'm trying to solve this problem but i can't...

the following table gives the variation of the field standard penetration number (N60) in a sand deposit (then there's a table)
if the groundwater table is located at a depth of 6m, dry unit weight of sand from 0-6m is 18kN/m^3 and saturated from 6-12m is 20.2kN/m^3, and D50 is 0.6mm, estimate the variation of the relative density with respect to depth.

depth (m) N60
1.5 6
3.0 8
4.5 9
6.0 8
7.5 13
9.0 14
i know i have to use this equation:


Dr(%) = ([ N60(0.23+0.6/D50)^1.7)/9] [1/sigma prime knot/pa])^0.5 x (100)

My only question is that since there are multiple depths... how do i go about calculating it?

 

[oldestguy]

In my view the N value related to other things is generally some person's idea of a correlation. If they were out on the jobs, they would see that all sorts of things can affect the number even if the soil does not change.

I'd shy away from any formula with "precision" relationships. It just ain't that good a "testing" system in my view.

 

[fattdad]

DM 7.1 or 7.2 has a graph showing the relative density as a function of blow counts. I think they use N1-60 values.

What is the actual engineering problem that you're trying to address? Is this for pile design, earht pressure, etc.?

I'm pretty sure that if you are normalizing blow counts for the purposed of determining relative density you have to adjust for 1 tsf of confining pressure. Your OP doesn't address this however. . .

f-d

¡papá gordo ain’t no madre flaca!

 

[dgillette]

"I'm pretty sure that if you are normalizing blow counts for the purposed of determining relative density you have to adjust for 1 tsf of confining pressure."

It looks like it does adjust for confining pressure. [1/sigma prime knot/pa])^0.5 looks just like Cn for liquefaction assessment, since pa is almost exactly 1 tsf.