DCP to SPT N-value correlations 2

[ragedriven]

Aside from a few graphs laying around the office here that appear to have been photocopied for the last 10 years... what is a reliable source for a DCP to SPT correlation?

idealy i'm looking for a graph of SPT N-value (blows per foot) VS DCP (blows per increment), with several lines plotted for various soil types.

 

[BigH]

ragedriven: Please identify the DCP you are discussing. As you will note from many threads that appear in these forums, there are an abundance of different "DCPs" in use - ranging from 2 inch cones driven by 65 kg hammer dropping 750mm, the TRRL miniature DCP, the Macintosh system (used in Malaysia), Sowers and others.

 

[cbosy]

Why bother using a DCP when you can use a static cone that has been very well correlated?

 

[msucog]

why use static cone when dcp is well correlated? why use either one? why use both? i think both have pros and cons. sometimes, a simple poking stick does better than both...but it's hard to put numbers to that.

i don't have any specific links handy to pass along. it might be wise to do some in-house correlations. try searching the forum since the subject has been discussed many times before.

 

[cbosy]

Boy, I wish I never said "a simple poking stick does better than both." I have used a manual static cone since 1984 in Florida and the Midwest very successfully and I swear by it. Geo Durham makes it.

 

[msucog]

notice i clarified my statement by saying "sometimes". either way, the instrument is only as good as the user.

 

[soileater]

I use a paper (attached) by the Minnesota DOT which correlates DCP (20mm/60° cone, 8kg weight, 575mm fall) with all sorts of stuff. You might find it useful.

 

[PSlem]

The graph is in SP399, an ASTM book you can get from Geo Durham. I take them as even in Piedmont soil up to N=12, which I feel is the limit for the smaller.

 

[Mickney]

Check out George F. Sowers and Charles S. Hedges "Dynamic Cone For Shallow In-Situ Penetration Testing" ASTM STP 399. Figure 3 shows penetration relationships between DCP and SPT for piedmont soils, coastal plain soils and piedmont alluvial soils. Hope this helps.

 

[ragedriven]

BigH, i should have specified, I'm referring to a sowers DCP manufactured by boart longshear, if i'm not mistaken it has a 15 lb hamer, 20" drop, 45° tip, seat 2", drive 1¾" for reading.

Typically i wouldn't really need these charts as i'm familiarized with piedmont soils in my major region, however i have a project in coastal plains deposits near a beach with high water table.

tests were done in the top 4' only with a D-50 going below that, i'm being asked to combine them into a log showing the entire boring.

the charts i've seen in the office here are from the sower's paper or his other work, just pour quality and hard to read, as sowers was a teacher of a few at my office. the charts have a soil chart for coastal plains but i don't trust it.

I've found out what i needed, thanks for the help everyone.

 

[jtjackson]

be very careful with those DCP numbers in sands if below the water table. They tend to go quick when you hammer the cone, making any data you obtain almost useless.