Calculating the Lateral Capacity of a pile 1

[western2000ca]

How difficult is it to calculate the lateral capacity of a pile by hand using the elastic solution? What would be a good book that shows how the elastic solution is arrived at (i.e. what assumptions are made, what are its limitations...etc.).

Secondly, how closely does the elastic solution methold compare to results using Brom's method.

Thanks in advance.

 

[FixedEarth]

It is not that hard to calculate it. "Foundation Design" by W.C. Teng, 1962 shows the equations from Hetenyi for free head and fixed head pier/pile that is laterally loaded. Included are equations for lateral deflection and bending moment with depth. It is neat.

Never compared the Brom's method with elastic method, so not sure about accuracy. Since Teng's book is rather hard to find, why not try Muni Budhu's foundations and earth retaining structures book. He has a free software that will calculate using his method. I checked his against Teng's 1969 method & they are very close.

 

[PEinc]

Teng's 1962 Foundation Design, Section 8-16, Table 8-3 on page 227 has info on allowable horizontal loads on vertical piles but no equations. Is 1962 the correct book?

http://www.PeirceEngineering.com

 

[FixedEarth]

PEinc

I owned this book for many years but only saw this page just recently! It is hard to find page.

Try page 272. Correct, it is 1962-I believe it is the only edition.

 

[PEinc]

Thanks. I only recently picked up a mint condition copy of the book. It still cracks when I open it.

http://www.PeirceEngineering.com

 

[dcarr82775]

Brom's (at least the method for clays that I am thinking of) is an ultimate resistance, not an allowable/elastic resistance

 

[PEinc]

In Teng's Section 9-10, Pages 271 to 273 address horizontal force on drilled caissons (drilled shafts) rather than a pile, as asked by western2000ca. I guess the assumption must be made that the equations also apply to a single pile.

http://www.PeirceEngineering.com

 

[western2000ca]

Thanks FixedEarth.

 

[western2000ca]

Fixed Earth,

How closely would the results obtained by using the equations in Teng's book compare with the results obtained using a program such as LPile?

Thanks

 

[FixedEarth]

western2000ca;

Not sure of those two comparisons. However, one one job I had last year, I did the Teng cohesive method (1969) which is not in his 1962 book & I had a required embedment of 14.2 ft. So we built the piers to 14.5 ft.

Then the client requested a finite element analysis as a presentation document and the requied embedment of the FEA analysis showed 14.1 ft. After that, I never questioned Teng's method. I have probably used his method on over dozen jobs in the past 3 years.

 

[PEinc]

Are you saying that you used the Teng method for piles rather than caissons? If so, thanks for the reference.

http://www.PeirceEngineering.com

 

[FixedEarth]

I used them for 18" diameter pier embedded 14.5 ft into very stiff clay. Not on piles yet. The only thing with Teng method is you don't get the lateral defelction at the ground surface directly. Comparing it with Budhu and Davies method (1986), I was able to determine that Teng deflection is between 1/4 and 1/2 inch. However the FEA showed deflection was only 0.2 inch.

 

[PEinc]

Teng's page 272 does have formulas for maximum horizontal displacement at the top of the drilled caisson. Wouldn't that give you the lateral deflection you wanted? Usually, the top of caisson is at or is very close to the ground surface.

http://www.PeirceEngineering.com

 

[FixedEarth]

PEinc;

That page is using Hetenyi's elastic method. It is based on horizontal subgrade modulus. Correct, it will give deflection values but it is not the Teng approcah.

If you go

http://www.steeltools.org

there is POLEFDN worksheet by Tomanovich. That spreadsheet has the 1969 method that I use.

Alternatively, if you take an equivalent square beam and support horizontally by vertical subgrade modulus but load it with (cohesion / width) you will get darn close to actual deflection curve. So say, k = 130 pci and loading of (1,000 psf/1.33*0.001 kip/lb) gives deflection of 0.14 inch. In addition you can get the point of fixity and maximum moment.

 

[PEinc]

Thank you. I will check out your information.

http://www.PeirceEngineering.com

 

[molerat2210]

Buy L-Pile. It's worth the investment if you do much with deep foundations. I think AASHTO Roads and Bridges has some methods hand calculations of lateral loads.

 

[irawanfirmansyah]

The most popular elastic method is Chang's method. This method uses linear subgrade modulus. Up to now, Japanese use this method to determine lateral capacity of pile corresponding to certain lateral deflection at pile head, say 1/4 ". You can find this method in most foundation text books.
Compare to LPile, this method is conservative. This can be understood since LPile adopts non-linear p-y curves in its analysis.
I did analysis for steel pipe pile of 600 mm diameter using both methods, and the allowable lateral capacities corresponding to 1/4" deflection (fixed head) are as follows:
- Chang's method : 11.5 tons
- Lpile : 14 tons
Broms method is for calculating ultimate lateral capacity of pile. Using this method Lateral deflection is unknown