Adhesion factors for Deep Foundations

[ktulu]

Just to see if anyone else had the same issue:

Problem #61 in the Geotech 6-minute solutions says use the adhesion factor method for determining the skin friction for a deep foundation, using the soil layer's cohesion.

CERM Table 38.4 list the adhesion factors for four cohesion values, which are widely ranged (from 500 - 3000psf) I took these to be ranges, but the solution uses some type of gray area in picking the adhesion factors (i.e. cohesion was 504, they chose 1.0, while I chose 0.83) You can see where my solution was lower than the solution.

Are the values for a range (maybe 0-500, 501-1000, 1001-2000, 2001-3000)? That is how I saw it....

Most likely, the cohesion values on the exam are going to be far enough away from a threshold (hoping) so this issue will not come up.

Anybody comes across something like this?

ktulu

 

[McEngr]

kt,

Are you taking the geo-depth module?

 

[ktulu]

Yes.

 

[Guest]

ktulu --

I have some education/background in geotechnical engineering, but not so much from the structural aspect.

When I have worked with pile design (and other deep foundations problems), I have been using a text - Geotechnical Engineering Pile Design and Construction, 1st Edition, Ruwan Rajapakse, P.E. It is a fairly straight forward text for practioners. It provides methodology and parameters based on design contraints and usually an example.

I believe you have asked the important questions when approaching the problem - what is the correct design methodology, what are the design constraints/assumptions, if there are any parameters missing how do I calculate or where do I find them. You have done as well as expected based on the example from "the other board"'s Six Minute Solns - the exam problem should be more clear about which approach and what factors would be necessary. If you feel there was a problem with 'decision-making' based on the wording of the exam problem you can always write that up on the after-exam survey. In this way, you can at least present your rationale and approach in case it differs from the exam makers.

Best of luck ... just one more week !!!!

JR

 

[EL Nica PE]

kt,

There are graphs for adhesion values. I think if you look in NAVFC you can find them. Let me know if you don't have it I can

post a copy of this graph.

 

[ktulu]

El Nica,

I'll take a look in NAVFAC and get back with you if I cannot find them...

Thanks

 

[ktulu]

Here is a couple Tables out of NAVFAC 7.2, including a more precise Table for the adhesion factors.

Thanks, El Nica....

ktulu

 

[Marissa]

Here is a couple Tables out of NAVFAC 7.2, including a more precise Table for the adhesion factors.
Thanks, El Nica....

ktulu

Ktulu,

Would you please tell me which table provides the more precise factors? I just wonder I have an out of date version.