Session 21

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Session 21 22 GROUP PILES

• Course S0484/Foundation Engineering
• Year 2007
• Version 1/0

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GROUP PILES

• Topic
• Bearing Capacity of Group Piles
• Group Efficiency
• Piles in Rock
• Consolidation settlement of Group Piles

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GROUP PILES
Lg (n1 1)d 2(D/2) Bg (n2 1)d 2(D/2)
Where D pile diameter d spacing of pile
(center to center)
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GROUP PILES
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GROUP EFFICIENCY

• Where
• group efficiency
• Qg(u) ultimate load bearing capacity of the
  group pile
• Qu ultimate load bearing capacity of each pile
  without the group effect

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GROUP PILES IN SAND
If ? lt 1 ? Qg(u) ?.?Qu If ?? 1 ? Qg(u) ?Qu
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GROUP PILES IN SAND
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GROUP PILES IN SAND
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GROUP PILES IN SAND
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GROUP PILES IN SAND

• Summary
• For driven group piles in sand with d ? 3D, Qu(g)
  may be taken to be ?Qu, which includes the
  frictional and the point bearing capacities of
  individual piles.
• For bored group piles in sand at conventional
  spacings (d ? 3D), Qg(u) may be taken to be 2/3
  to ¾ times ?Qu (frictional and point bearing
  capacities of individual piles)

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GROUP PILES IN SATURATED CLAY
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GROUP PILES IN SATURATED CLAY

• Calculation steps
• Determine ?Qu n1.n2 (Qp Qs)
• where
• QP 9 . cu . Ap (ultimate end bearing capacity
  of single pile)
• QS ?(?.p.cu.?L) (skin resistance of single
  pile)
• Determine the ultimate capacity by assuming that
  the piles in the group act as a block with
  dimensional Lg x Bg x L as follow
• - end bearing capacity of the block
• QP Ap . qp Ap . cu . Nc with Ap Lg . Bg
• - Skin resistance of the block
• QS ?(pg.cu.?L) ?2.(LgBg).cu.?L
• - Daya dukung batas tiang grup
• ?Qu QP QS
• ?Qu (Lg . Bg) . cu . Nc ?2.(LgBg).cu.?L
  
• Compare the values obtained in step 1 and 2 ? the
  lower of the two values is Qg(u)

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GROUP PILES IN SATURATED CLAY
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GROUP PILES IN SATURATED CLAY
Problem The section of a 3 x 4 group pile
layered saturated clay. The piles are square in
cross section (14 in. x 14 in.). The center to
center spacing, d, of the piles is 35 in.
Determine the allowable load bearing capacity of
the pile group. USE FS 4
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GROUP PILES IN SATURATED CLAY
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PILES IN ROCK
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CONSOLIDATION SETTLEMENT OF GROUP PILES

• The Terzaghi formula is valid with some rules
• The consolidation settlement is occurred from the
  depth of 2/3 of pile length.
• The stress increase caused at the middle of each
  soil layer by using 21 method

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CONSOLIDATION SETTLEMENT OF GROUP PILES
Problem A group pile with Lg 3.3 m and Bg
2.2 m as shown in the figure. Determine the
consolidation settlement of the pile groups. All
clays are normally consolidated.
?sat 18 kN/m3 Cc 0,3 eo 0,82
?sat 18,9 kN/m3 Cc 0,2 eo 0,7
?sat 19 kN/m3 Cc 0,25 eo 0,75
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ELASTIC SETTLEMENT OF GROUP PILES

• VESIC

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ELASTIC SETTLEMENT OF GROUP PILES

• MEYERHOF (Pile groups in sand and gravel)

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ELASTIC SETTLEMENT OF GROUP PILES

• PILE GROUP SETTLEMENT RELATED TO THE CONE
  PENETRATION RESISTANCE

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UPLIFT CAPACITY OF GROUP PILES
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UPLIFT CAPACITY OF GROUP PILES