pile group effects reduction factors in bedrock
pile group effects reduction factors in bedrock
(OP)
Currently the CBC requires reduction factors to account for group effects
- on lateral behavior when pile spacing is less than 8D (D-pile diameter)
- on axial behavior when pile spacing is less than 3D (1810.2.5).
Local and federal agencies came up with different reduction factors. Have you seen any group effects reduction factors tailored for different foundation earth materials (i.e. alluvium, bedrock)? A colleague suggested using reduction factor of 1 for lateral behavior when pile spacing is more than 4D, but he couldn't provide any document to support it. Thanks.
- on lateral behavior when pile spacing is less than 8D (D-pile diameter)
- on axial behavior when pile spacing is less than 3D (1810.2.5).
Local and federal agencies came up with different reduction factors. Have you seen any group effects reduction factors tailored for different foundation earth materials (i.e. alluvium, bedrock)? A colleague suggested using reduction factor of 1 for lateral behavior when pile spacing is more than 4D, but he couldn't provide any document to support it. Thanks.





RE: pile group effects reduction factors in bedrock
For point bearing pile recommendations, see page 33,34 & 35.
For friction pile recommendations, see pages 35 & 36.
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RE: pile group effects reduction factors in bedrock
How about the lateral behavior? CBC requires to consider group effects on lateral behavior when spacing is less than 8 pile diameters. Shall these reduction factors be any different for piles in bedrock? Or shall we use at all reduction factors for piles in bedrock?
RE: pile group effects reduction factors in bedrock
If this is a marine structure (for example a pile supported pier), where bedrock is very shallow, I would use some reductions for the lateral subgrade reaction of the rock. Here in Japan, we have reduction factors that account for this. The Japanese methodology is also explained in the Reese and Van Impe book.
RE: pile group effects reduction factors in bedrock
RE: pile group effects reduction factors in bedrock
I think that if your bearing layer (bedrock) is deep, it may not be affected by lateral loading and therefore reductions may not be required at this level.
I would also like to hear the opinion of other geotechs...
RE: pile group effects reduction factors in bedrock
RE: pile group effects reduction factors in bedrock
RE: pile group effects reduction factors in bedrock
RE: pile group effects reduction factors in bedrock
m = 1 -0.2 * (2.5 - s/b), s < 2.5 b
where s = center-to-center distance between piles and b=pile diameter.
Reese and Van Impe book indicates that the above equation is less conservative than other methods but I am located in Japan so I have used it for my projects.
If you find other reference, we will be more than happy if you can share them with us..