Lecture 18 - DF46 PILE GROUP CAPACITY (the whole is...

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DF46 PILE GROUP CAPACITY (the whole is sometimes less than sum of the parts) where: P ag = allowable capacity of a pile group η = group efficiency factor N = number piles in the group P a = allowable capacity of single, isolated pile Group efficiency is a function of soil type, the pile c-c spacing to pile width ratio (s/B), the pile length to width ratio (L/B), the number of piles, and the shape of the group Pile cap bearing not added unless cap will remain in contact with soil (no fill settlement) and piles will fail individually (s/B >8) End bearing piles resting on rock , dense sand, gravel, or limerock: often assume η =1.0 Driven friction piles in sand (cohesionless): assume η =1.0 (conservative) driving installation densifies sands and improves capacity (drive from the center out, cofferdams provide false confinement), for loose sand with s/B 2 b , η = 1.0 - 2.0, for dense sand with 2 < s/B < 4 b η > 1.0 Drilled shafts in sand and jetted or predrilled piles, η 0.67 Driven friction piles in cohesive soil – approximations 1. Converse-Labarre Formula (Bolin, 1941) where θ , degrees = arctan s B m = # of rows of piles n = # of piles in a row B = pile diameter or width s = center to center spacing of piles (not the clear distance
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Lecture 18 - DF46 PILE GROUP CAPACITY (the whole is...

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