Soil spt test and N values
Posted 10 February 2008 - 10:15 PM
I am a college senior that is in the last semester of civil engineering program. I am working on an assignment that requires calculating the N values for a given boring log. I know that you ignore the first 6 inches and then use the next two sets of data of the next foot to get the N value, but how do you begin the N table? Do I record the N value at 6" or at 1 foot? I am starting from ground level and test goes to 102 ft. I am assuming that I would take the value for 6" to 18" and enter it for a depth of 6". Then my next depth would be 3' and and would enter the data at 2', using the blow counts from 2' to 3', continuing to the end. If anyone can help clarify this that would be great. Thank you very much.
Posted 10 February 2008 - 10:19 PM
Posted 10 February 2008 - 10:54 PM
If you take a look at your report, please note the following:
1. You are using a split spoon sampler device as indicated by the SS notation in Sampler Type;
2. The recovered cores are based on 2-ft intervals (e.g. S1, S2, etc) which is consistent with SPT ASTM;
3. Measure intervals are on 0.5-ft (6") intervals, which is again consistent with SPT ASTM;
So, if you are following the ASTM as described by Old as Dirt Geo, you are supposed to take the 2-ft interval and knock off the first and last blow count and use the middle two blow counts for the N-value.
That N-value will be attributed to the 0' - 2' length of the soil profile.
You will repeat this procedure for each 2-ft interval so your table will look like:
0' - 2'
2' - 4'
4' - 6'
6' - 8'
and so on
If you are interested in reading more about applicability of the SPT, you can try these two documents:
Unified Facilities Criteria - Soil Mechanics (Replaced NAVFAC 7.01)
Subsurface Investigations - Geotechnical Site Characterization (FHWA NHI-01-031)
I hope this helps!
Posted 11 February 2008 - 01:12 AM
Posted 14 July 2009 - 06:59 AM
hey guys see http://www.novotechsoftware.com/spt/ for SPT correlations program (FREE).
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