Determination of pre-consolidation pressure by strain-energy method

[geoman110]

Hello,
Our laboratory only uses typical Casagrande method for determination of pre-consolidation pressure in conventional consolidation tests. I am planning to introduce a second option and currently my first choice is strain-energy method such as Tavenas method. There are two questions here:
1 – Does anyone have a comment in regard to using strain-energy method for determining pre-consolidation pressure. Most of the published papers are calling it a more accurate and easier to use method. I am wondering if you have come to the same conclusion in real life experience/project?

2 – I have read a few published papers on this topic and there are a few methods for strain-energy which are slight different. However, in order to use it in practice, I prefer to use a method that is endorsed by a standard. I could not find anything in ASTM. Is there any standard that endorsed this method?

Thanks in advance.
Regards, geoman110

 

[BigH]

Have never used it - it is outlined in Bowles 5th edition. Why not check out logp'-loge? There are some good papers out there that show this method - results in two straight lines and the intersection is the pre-consolidation pressure.

 

[geoman110]

Thanks for the reply BigH
I will check out the suggested method and also dig more into the Strain-Energy method. I will keep everyone posted of the outcome. Meanwhile, if anybody has more comments, it is greatly appreciated

 

[paganel]

Pacheco Silva’s method from south america is also convenient to use and also independent of the graph scale.

Pacheco Silva, F. 1970. A new graphical construction for determination of the pre-consolidation stress of a soil sample. In Proceedings of the 4th Brazilian Conference on Soil Mechanics and Foundation Engineering, Rio de Janeiro, Brazil. Vol. 2, No.1, pp. 225–232.

 

[BigH]

I've told this story before - but Casagrande used to consult with my company back in the late 60s as our President at the time was a former student. He came up to Toronto and an eager young engineer showed him all these beautiful Casagrande constructions he had done on quite a number of consolidatoin tests. Casagrande looked at them and suggested a few changes here and there . . . the engineer asked him - "But, I did them according to your method." Casagrande replied that, yes, you did but the construction method was developed to "teach" my students how basically to estimate it.

 

[geoman110]

Hello everyone, thanks for the reply.

BigH, I am not sure if I understand the meaning of your story correctly. Did Casagrande mean his method is just estimation or there is something else that I am missing?

In respect to the strain-energy method, I have done some research and so far it appears a good secondary/confirmatory method. However, I am not done reading and cannot come to a final conclusion yet. I will keep everyone posted when I have finished reading all the collected references.

 

[BigH]

In looking at the various different types of curves one gets in consolidation testing (what about those that aren't "straight" in the primary consolidation range) - a lot is a matter of judgment of which he had plenty. How does one take experience and judgment and teach students? You make up a methodology that will get the student, typically, in the right ballpark. The construction method he developed and taught was simply that, a teaching tool.

 

[geoman110]

Well said BigH. Thanks for the reply