1. Course : S0484/Foundation Engineering Year : 2007 Version : 1/0
Session 21 – 22 GROUP PILES

2. GROUP PILES
Topic:
Bearing Capacity of Group Piles
Group Efficiency
Piles in Rock
Consolidation settlement of Group Piles

3. GROUP PILES Where: D = pile diameter
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)

4. GROUP PILES

5. 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

6. GROUP PILES IN SAND
If  < 1  Qg(u) = .Qu
If  1  Qg(u) = Qu

7. GROUP PILES IN SAND

8. GROUP PILES IN SAND

9. GROUP PILES IN SAND

10. 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)

11. GROUP PILES IN SATURATED CLAY

12. 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.(Lg+Bg).cu.L
- Daya dukung batas tiang grup
Qu = QP’ + QS’
Qu = (Lg . Bg) . cu . Nc* + 2.(Lg+Bg).cu.L
Compare the values obtained in step 1 and 2  the lower of the two values is Qg(u)

13. GROUP PILES IN SATURATED CLAY

14. 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

15. GROUP PILES IN SATURATED CLAY

16. PILES IN ROCK

17. 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 2:1 method

18. 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

19. ELASTIC SETTLEMENT OF GROUP PILES
VESIC

20. ELASTIC SETTLEMENT OF GROUP PILES
MEYERHOF (Pile groups in sand and gravel)

21. ELASTIC SETTLEMENT OF GROUP PILES
PILE GROUP SETTLEMENT RELATED TO THE CONE PENETRATION RESISTANCE

22. UPLIFT CAPACITY OF GROUP PILES

23. UPLIFT CAPACITY OF GROUP PILES