More Lateral surcharge questions 4

[RFreund]

I have the same questions as the OP in this post: thread255-102196 . (Question was never really answered) I understand the FoS of 2.0, but why does Das show the equation for a strip loading as:
Sigma(x)=2q[Beta-{Sin(Beta)(Cos(Beta))}]/H

and multiple other sources as:

Sigma(x)=2q[Beta-{Sin(Beta)(Cos(Beta))}]/Pi

Why H as apposed to Pi, which is correct?
Or is this another typical geotech answer: Both, sometimes..

EIT

 

[tumbleleaves]

I say the first equation is incorrect. The equation appears dimensionally incorrect and gives units of pcf. I'm assuming q is in psf?

Textbooks even excellent textbooks have typos and errors. The Das book didn't serve me outside of college. I held onto it and it occupies a space on my shelf, the Bowles book did get used in practice--but even then after I gained more experience the Bowles book became less relevant. What I liked about Bowles (is he alive?) was the practicality of the book and that he was quick to point out the limitations of the theory and bluntness of the approximations. Seemed like there was more engineering personality in the Bowles book. Ooops I'm way off topic.

Did I pass the test? Was equation #2 the correct equation?

 

[RFreund]

I believe the second to be correct as it appears in many other publications. A typo is very plausible.

EIT

 

[tumbleleaves]

The equation that appears in the most publications is correct: "Engineering by democracy"

An amusing thought.

Are you sure there is a safety factor of two built into those equations? I don't remember that. What for? Why is two the mathemagical safety factor for "elastic" surcharges.

I remember one place I worked at we had a slick looking computerized calculation for the wheel loads of various vehicles using boussinesq. Individual wheel loads cool looking graphs, the works, it looked so good it had been used for years, well before I had worked at the firm. One day I analyzed it discovered it had an impact factor of 1.3 built into it and also mistakenly used the axle weights for wheel loads. GARBAGE IN GARBAGE OUT.

I pointed out the mistake and did not use it for any of the work that I was in charge of, but the people that were there had been using it so long they didn't even change it. They didn't understand wheel loads anyways, it was a waste of breath.

Mothers are under the false impression that all scientists and engineers are smart.

 

[FixedEarth]

This is covered nicely in "Substructure Analysis & Design" book by Paul Andersen, 2nd ed., pages 32-35.

 

[PEinc]

Check out this previous discussion in thread255-260153.


www.PeirceEngineering.com

 

[PEinc]

One more prior reference attached.

www.PeirceEngineering.com

 

[PEinc]

And another.

www.PeirceEngineering.com

 

[tumbleleaves]

If only my memory were so faithful: I was surprised I spelled Boussinesq correctly.

The equation with the two in it looks the most familiar. I'm not going to dig up my Bowles book to check if that one didn't have the two (I'll take your word for it). I had to down-size and don't have room to store my books, they're packed away and unorganized.

It did seem that the Boussinesq pressures were nearly always conservative, compared to say the 2 ft surcharge used to design some permanent concrete structures that could be supposed to be non-yielding. Also, if I remember correctly Boussinesq pressures became typically negligible by about a depth of 20 ft or so. The only time I remember using Boussinesq was in temporary shoring design.

 

[RFreund]

PEinc - Thanks for the links. I never thought my career as a structural would be so involved in the Geotech world.

Fixed Earth - Thanks for the reference however "Substructure Analysis & Design" book by Paul Andersen, 2nd ed. seems to be a rare find but I'll keep my out for it. Is it a good general reference?

Thanks all.

EIT

 

[FixedEarth]

RF;

Attached are few pages from the text. It is a great book, but true, it is hard to find it.