Preconsolidation Pressure_Consolidation test results

[Geo2014]

Hello,
Is there a any easy way to read preconsolidation pressure from the test result (xsl) format? I tried to draw a tangent line using excels "Add trendline " function but it didn't worked.

 

[BigH]

You could try plotting log p' vs log e (or log strain) and you should get "two" straight lines - where they match up would be, approximately, the preconsolidation pressure. You might try plotting as two inputs rather than one and then match up the equations as to what point they are equal. Of course, I do things the old school way. . . .

 

[fattdad]

if you are using a consulting laboratory and have specfied the ASTM standard, the lab report should present Pp. You can read the ASTM standard and they'll explain the approach to determining Pp also.

f-d

¡papá gordo ain’t no madre flaca!

 

[oldestguy]

What's wrong with pencil and paper?

 

[fattdad]

Dear Geo2014,

If I gave any indication that this was not a manual procedure, excuse me. For some reason, it appears that Mr. Oldestguy thinks I was referencing a digital proceedure.

The truth (as I see it) is the "determination" of Pp is open to interpretation. To interpret the point of maximum curvature, to interpret the tangent line, to bisect an angle, etc. Each of these manual interpretative steps can lead to a different conclusion. My practice is to take the consolidation data points and manually draw in the e-log-p curve then do the Pp interpretation. Then redo the entire process. You may find that you Pp values vary as a result of your interpretative process. Often the spread of your interpretative range is the direct consequence of sampling disturbance or laboratory precision.

I always consider this a manual process and hope I didn't suggest otherwise. If in doubt check the proceedures shown in the ASTM.

f-d

¡papá gordo ain’t no madre flaca!

 

[BigH]

Again - try plotting (by hand) log p' against log e (or log strain) - they come to two straight lines that meet (the recompression line and the compression line) - and that is dang close to any other methodology of determining the preconsolidation pressure. Years ago, Casagrande (I think it was Arthur, not Leo) came to Geocon's office (Canada's Geocon - the original) as he was doing some consulting work with one of his former students. Well, as the story goes - and it was a bit before my time - one young engineer had plotted out quite a few consolidation curves and was proud to display them to Casagrande. He looked at them and said, "I think this should be a little bit more over to this side; that one's okay but this third one, slightly to the higher side." The young engineer was bewildered as he had spent a lot of time going through the procedure for "getting it right." Arthur consoled the young lad saying that he developed the "method" as a way of teaching his students how to get it - approximately . . .

http://www.astm.org/DIGITAL_LIBRARY/JOURNALS/GEOTECH/PAGES/GTJ10974J.htm

There is also a paper in the EIGJ (that on line journal) about it - I have it somewhere and will, when I have time, try to find it.

 

[BigH]

See the following (you can google it)

Senol and Saglaner "Determination of Preconsolidation Pressures with a new Strain-Energy - log strain Method". EJGE Paper Number 0015, Yr-2000.