Battered Piles working in Tension and Compression

[scarr1]

I am designing a 7 story concrete building. Lateral system: shear walls. Foundations: Micropiles. I have huge lateral loads on this structure because: 1. I am holding back 20' of earth on two sides (non-opposite sides). 2. The structure is highly irregular and stiff (high seismic loads).

I want to use battered piles to resist the lateral loads under the shear walls. My geotech report says that I can use the horizontal component of the pile's axial capacity to resist lateral loads. Would it be more correct to use the horizontal componant of the axial load that is actually acting on the pile at the time of the shear load as resistance for the lateral?

Also, the piles can be designed to resist about half of their axial capacity in tension. If i batter the piles away from the direction of the shear, can i use the pile in tension (once vertical loads have been overcome) to resist the lateral loads. Wouldn't it be more efficient to batter the piles in this way (tension) because then the vertical loads on the pile are actually off-setting the tension imposed by the lateral loads?

Thank you for your help.

 

[Qshake]

You might want to consider supplementing the micropile with other piling as micropile are not an efficient means of transferring lateral loads in the first place.

Regards,
Qshake

Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

 

[BigH]

I think that I would use some soil nails (or ground anchors) to build a tied-back wall - then you will have greatly reduced lateral pressures on your walls. Hold back your walls independently. I agree that even with batter, micro-piles would likely not have significant lateral capacity.

 

[Focht3]

I don't like the idea of battered piles in high seismic areas. I'd use another system. Remember the expression, "load seeks resistance." The battered piles will create "hard" spots - with damage likely in a seismic event.



Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora. See faq158-922 for recommendations regarding the question, "How Do You Evaluate Fill Settlement Beneath Structures?"

 

[DRC1]

The advantage of battering compression piles is that the skin resitance in tension is essentially the same as in compression, however in compression you have the added capacity of the bearing component. This is not available for the tension pile, once it pulls, thats it.

 

[babilu]

bettered piles are significantly reduces the lateral loads. but remember it makes your building very stiff. i mean very very stiff.
it can be harmful. You decide to fight agains a nature forces, not just follow it.

Remember strong tree are easy to fall against the strong wind than the skinny tree.

Battered pile in bridges is not to counter full effect of earthquake.

Why dont you solve the opposites building walls with ground achored sheet pile...?

 

[BigH]

If he has room, I still think that tie-backs on the earth retaining walls would be a positive step. To back up Focht3, as I've mentioned in other threads, one should read about the Nagata Earthquake (1964) - they found that pile caps of battered piles were significantly damaged as a result of the battering.