Pullout capacity of Channel or I Section

[nagatalluri]

Guys:

Can anybody suggest an empirical method or rule of thumb for measuring the pullout capacity of the Channel or I sections driven into soil based on the SPT bore log information?

We generally perform pullout tests to estimate this but trying to get an estimation prior to pull out tests in order to optimize the length of pile to be tested.

Thanks
NT

 

[jonastp]

Hi,

I usually consider the compressive resistance of the pile based on effective stress calculation (Beta method), and used more or less 75% of the capacity that is available in pullout (it can be up to 100% in clay, and between 50 to 80% in cohesionless material). for more info on the effective stress calculation you can find a book by Dr. Bengt Fellenius here ([URL unfurl="true"]http://www.fellenius.net/papers/350%20Red%20Book%20-%20Basics%20of%20Foundation%20Design.pdf[/url]), chapter 7 would be very helpfull for you.

As for the circumference used for calculation, I used (and it is the accepted method) a rectangle which sides are the depth and width of the I section.

Hope it helps a little.

 

[nagatalluri]

Sir

Thanks for your input. If I understand correctly, for perimeter you are considering the dimensions of the I-section and summing it up (two times the flange width + 2 times the web height)??

Please let me know

Thanks
NT

 

[jonastp]

Exactly!

 

[nagatalluri]

Also in the remolded state the clay cohesion is going to reduce (some times negligible). Principles of Foundation Design by B M Das is considering the effective cohesion as zero.

In case if the water table is deep enough (around 25') where the pile length is only 10' can we consider the undrained shear strength as effective cohesion or reduce it by may be 50% and use it the calculation?

What is your experience?

Thanks
NT