Determination of Lateral Capacity of Piles for Bridge Foundation

[GTEngr]

I am currently redesigning a 3 span, single lane bridge. According to my calculations, the bridge is failing due to sliding, but I have not considered the lateral capacity of the pile (2 rows of 6 piles each) as a part of the resisting forces. I would like to include these in order to avoid increasing the dimensions of the footing, but the soil geotechnical report does not provide these values. Is there a way that I can estimate this? Also, should I consider the piles acting together as one unit or individually?

The piles are concrete (.3m x .3m) spaced at 1.36m apart center to center. The soil at the tip of the pile is considered to be "dense to very dense gray coarse gravel"

Thank you

 

[PEinc]

You need to do a lateral analysis of the foundation piles and pile cap. Usually, the geotech will do this using LPile or AllPile.

http://www.PeirceEngineering.com

 

[PEinc]

Both programs use Com624 for the lateral analysis.

http://www.PeirceEngineering.com

 

[PEinc]

Also, competent soil near the top of the pile is more effective for providing lateral resistance than competent soil near the pile tip.

http://www.PeirceEngineering.com

 

[GTEngr]

PEinc,

Thank you for your response. Unfortunately, I do not have access to this software, and I am unable to get this information from the geotech consultant. The bridge is actually located in Cambodia, and many of the consultants used for the project are difficult to contact. Is there any method for conservatively estimating the lateral capacity of the piles without the use of software? I found some specs used in India, which require calculating the force needed to displace the pile by 5mm, and using this force as the lateral capacity. This method requires analyzing the pile as a cantilever and determining the point of fixity of the pile. Unfortunately, I also do not know how to determine the point of pile fixity, but was assuming that approximating ~1/3 of the pile length would be sufficient. Do you have any further recommendations? Thank you again.

The soil characteristics are as follows:
firm brown silty clay (2m)
loose brown, yellow silty fine to coarse sand (4.5m)
medium dense light-gray clayey coarse sand (1.5m)
stuff yellow, gray silty clay (1.5m)
dense to very dense gray coarse gravel (6m)
*pile length is 10m

 

[PEinc]

I believe that COM624 is a free download from FHWA. Without this software, you could possibly design the bearing piles for the lateral load as very short, cantilevered soldier beams that are laterally supported by passive resistqance. This will give you the piles'bending stress and structural steel deflection but not soil movement. This isn't as accurate as using LPile or AllPileb but is better than no analysis. You may also want to check NAVFAC DM-7. There probably is graphical info in there on lateral resistance of bearing piles. DM-7 is also a free download.

http://www.PeirceEngineering.com

 

[moe333]

Do a google search for "Duncan and Evans" + lateral loading of piles. They developed charts and equations for the same P-Y analyses that LPile uses.

 

[aeoliantexan]

Yes, DM-7.02 has a graphical procedure beginning on Page 7.2-234 in my copy. I used to use it before we got L-Pile.

 

[GTEngr]

Thank you all for your help. I actually found the following document used in India, which was fairly easy to use for anyone else having a similar issue (the cover page is also quite catchy):

https://law.resource.org/pub/in/bis/S03/is.2911.1.1.2010.pdf

As a side note, unfortunately, FHWA no longer has COM624 available for download.