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RE: Battered piers/piles

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> 1. Can drilled concrete shafts be installed with a batter? (I would
> think not, but I've heard rumor that it has been done before.)

In the right soil with a competent crew a drilled shaft can be drilled at a
slight batter.  Actually, with an incompetent crew it's very likely every
shaft is drilled at a batter.


> 2. If I have a deep soil retaining structure with significant lateral
> load, I can come up with battered steel H-piles driven to refusal in
> rock to resist the lateral load (2V:1H batter). But if I assume that the
> pile resists the load axially, there is a significant vertical component
> that exceeds the total vertical load of the structure - what happens to
> the excess vertical reaction from the pile? (Most references I've seen
> say to design the battered pile for the total lateral load but do not
> address what to do about unbalanced vertical loads. But it seems that
> the free-body diagram does not balance. How do bridge abutments using
> battered piles handle this?)

It looks like you're assuming a pure axial reaction in your piles, which is
how the classic pile design works.  Because of the shallow angle of the
batter, the vertical component of the force in the battered pile sometimes
does exceed the gravity load.  This is handled by the vertical piles in
tension.

If you have *only* battered piles, then the classic design assumptions won't
work unless your pile batter is less than the angle of the lateral + gravity
applied force resultant.  To satisfy statics you have to include the lateral
soil forces on the side of the piles and the bending moments induced by
those forces.

Also, if the lateral loads are high, gravity loads are light, and the
lateral capacity of the soil is low (soft clay or loose sand), then your
analysis might be exactly right - the structure will fail by riding the
piles sideways and upwards in an arc.

> 3. Similarly, if I remove the lateral load but still want to resist
> vertical load (such as for dead weight without applied lateral load),
> the vertical reaction in the battered pile creates an unbalanced lateral
> load (if it acts axially). What happens to the unbalanced lateral load?
> (My proposed solution is to install equal and opposite battered piles to
> exactly offset the lateral load - and neglect these battered piles when
> in tension for the laterally loaded case.)

The extra lateral load caused by the pile can be resisted either by soil
pressure on the side of the piles, mirrored battered piles, or by passive
pressure back against whatever is causing the lateral load.

Jason

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