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Pile Group Analysis

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BNGeo

BNGeo

Geotechnical
Nov 28, 2023
19
Modeling a pile group with an "I" shape (group of piles at the top and bottom of the "I", tied together). I'm looking for some insight as to if the results I'm seeing "make sense." This particular scenario has 1000k compression on the top of the "I" and 1000k tension on the bottom of the "I". As you'd expect, the results are the the piles in compression end sum to about 1000k and the piles in the tension end sum to about 1000k.

But, if I apply a shear load to the top of the "I" of 500k (loads applied at the elevation of top of piles, which are buried), then I get a massive increase in the piles that are in tension, of almost 4x the scenario where there was no shear load. Sketch attached.

Can anyone suggest why the shear load add such a large amount of tension? I can't seem to recreate this tension on paper via simple sketches.
 
 https://files.engineering.com/getfile.aspx?folder=ed8c7f55-163c-4c53-b473-f69f6700d117&file=sketch.pdf
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Can anyone suggest why the shear load add such a large amount of tension?
Click to expand...

If the model assumes the compression piles are point bearing, and the length of the compression piles is several times the horizontal distance between the compression & tension loads, and the soil is assumed to be unable to resist horizontal loads... there is a way to get your results:

The 500K horizontal shear creates an overturning moment (500K x 6X in my example). The only way to resist this moment is more tension in the tension piles (1000K + 3000K = 4000K, in the example).

Pile_Cap-600_hpy7tx.png
 
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It is not reasonable to get 4 times tension. Check your model. The piles must have lateral soil resistance to resist the applied shear .
Pls post your model and soil parameters (lateral springs etc) to get better responds.
...



He is like a man building a house, who dug deep and laid the foundation on the rock. And when the flood arose, the stream beat vehemently against that house, and could not shake it, for it was founded on the rock..

Luke 6:48

 
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Assuming the model includes lateral soil springs, there is a theoretical centroid of lateral resistance at some distance below grade (say 6X). The eccentricity between that centroid of resistance and the applied lateral load creates an overturning moment. That overturning moment is resisted by the compression-tension couple in the two pile groups.
 
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