168_CEG 4012 Notes Fall 2011 CEG 4012 Notes Fall 2011

168_CEG 4012 Notes Fall 2011 CEG 4012 Notes Fall 2011 - ==...

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/ ~ I / '- '- '- '- where DF46 PILE GROUP CAPACITY (the whole is sometimes less than sum ofthe parts) P aQ = 11 N Pa I where: P ag = allowable capacity of a pile group 11 = 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 (sIB), the pile length to width ratio (UB), 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 (sIB >8) End bearing plies resting on rock, dense sand, gravel, or Iimerock: often assume 11 =1.0 Driven friction plies in sand (cohesionless): assume 11 =1.0 (conservative) driving installation densifies sands and improves capacity (drive from the center out, cofferdams provide false confinement), for loose sand with sIB
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Unformatted text preview: == 2 Q, 11 = 1.0 - 2.0, for dense sand with 2 < sIB < 4 Q 11 > 1.0 Drilled shafts in sand and jetted or predrilled piles, 11 == 0.67 Driven friction plies In cohesive soli - approximations 1. Converse-Labarre Formula (Bolin, 1941) = 1-a r(n-1)m+(m-1)nl 11 90 mn 9, degrees = arctan (:) 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) Example: Find allowable capacity of the pile group at right for a FS =2 Pile diameter = B = 1 ft, Pile spacing = s = 3 ft on center Friction piles in cohesive soil P u (single pile) = 100 Kips. 0 0 0 I L (e.,-1)"3 + 0-1) ~ ] s 11= ,-,.r(H,i1 ( +)) '10 ( J) (11) =o.1-\----L.--+-o(-0 0 0 P a (single pile) = 100/:)" :-5"0 k;fS 0 0 0 0 P ag (group) = (0.1-1) (I-;k p;)es) (S () k) = 'f '2. () k;/s...
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