Lateral Capacity Piles | Options
Lateral Capacity Piles | Options
(OP)
Maybe this should be in geotech forum... but
I have a relatively long (~175ft) building that is relatively light (steel job). Due to nearby below grade structures we are required to use piles even though the soil is decent. The problem I'm having is that the number of piles required for vertical load is far less than that required for lateral load. The piles that we are using based on the geotech report/design have 100T compression capacity and 4T lateral. Piles are expensive so adding piles for lateral base shear only is a tough pill to swallow.
I'm thinking that this must be a common problem. Do you ever use a shear key for an overall building? If you add up all the pile caps they pretty much do it on their own.
I have a relatively long (~175ft) building that is relatively light (steel job). Due to nearby below grade structures we are required to use piles even though the soil is decent. The problem I'm having is that the number of piles required for vertical load is far less than that required for lateral load. The piles that we are using based on the geotech report/design have 100T compression capacity and 4T lateral. Piles are expensive so adding piles for lateral base shear only is a tough pill to swallow.
I'm thinking that this must be a common problem. Do you ever use a shear key for an overall building? If you add up all the pile caps they pretty much do it on their own.






RE: Lateral Capacity Piles | Options
RE: Lateral Capacity Piles | Options
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RE: Lateral Capacity Piles | Options
I'm told (by multiple sources) that no one batters piles in my area because in general these are very narrow sites, 25ft range typical so with 60ft to 100ft piles it's difficult.
RE: Lateral Capacity Piles | Options
RE: Lateral Capacity Piles | Options
The only time I've used a "key" is with a retaining wall. But to answer your question: Sometimes I have successfully used the passive pressure developed against the slab of a building (if I am satisfied that the ground adjacent to it will remain undisturbed, paving will generally guarantee that) to resist lateral loads.
RE: Lateral Capacity Piles | Options
1) Turn a blind eye altogether.
2) Assume passive / at rest / active pressure against caps and grade beam corners depending on your belief system. Evaluation of the movement required to develop the resistance is always a thing.
3) Make some assumption about the friction generated on the sides of your grade beams as a result of translation through the soil.
4) Tie your grade beams and pile caps to the SOG and assume that you're engaging every damn pile you!ve got.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Lateral Capacity Piles | Options
A note for bookowski: be careful with this. (Really any kind of friction if I understand your problem correctly.) Reason being: a lot of your vertical load should run directly into the piles......ergo it won't be available for frictional (sliding) resistance.
RE: Lateral Capacity Piles | Options
RE: Lateral Capacity Piles | Options
RE: Lateral Capacity Piles | Options
IFRs - This was basically an idea that the geotech had. We have 9.5" piles and he suggested that maybe for the top X feet they could enlarge it to increase the lateral. He wasn't sure about the analysis off the top of his head but thought it might be possible, if tricky to build.
Retrograde - This idea also came up and might be an option if there's no other way.
The allowable pile load is based on 1/2" lateral displacement. We're in good soil - it seems to me that there has to be a lot of cumulative other stuff helping, friction and passive etc. If I was on junk soil I wouldn't be so gung ho for that approach.
RE: Lateral Capacity Piles | Options
RE: Lateral Capacity Piles | Options
- If the soil pressure against the caps gets it done, I could certainly get behind that. I've seen engineers backfill with lean mix in attempt to reduce the displacement at which resistance kick in.
- Maybe the geotechnical engineer would consider improved values if you detailed a fixed head condition.
- How short is the short plan dension?
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Lateral Capacity Piles | Options
RE: Lateral Capacity Piles | Options
SU10 - Yes, the allowable for this is "1/2 the load which produces 1" of lateral deflection" - so 1/2" basically, assuming it's linear. I agree that this should be plenty to engage passive pressure, especially if we used Kootk's lean concrete backfill idea. Just need to get the geo on board. I'll go back and press this idea.
RE: Lateral Capacity Piles | Options
RE: Lateral Capacity Piles | Options
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Lateral Capacity Piles | Options
Robert Hale, PE