1. Session 19 – 20 PILE FOUNDATIONS
Course : S0484/Foundation Engineering
Year : 2007
Version : 1/0
Session 19 – 20 PILE FOUNDATIONS

2. PILE FOUNDATIONS
Topic:
Settlement of Piles
Laterally Loaded Piles
Pull Out Resistance of Piles
Pile Driving Formula
Negative Skin Friction

3. S = S1 + S2 + S3 Where: S = total pile settlement
SETTLEMENT OF PILES
S = S1 + S2 + S3
Where:
S = total pile settlement
S1 = elastic settlement of pile
S2 = settlement of pile caused by the load at the pile tip
S3 = settlement of pile caused by the load transmitted along the pile shaft

4. SETTLEMENT OF PILES Where:
Qwp = load carried at the pile point under working load condition
Qws = load carried by frictional (skin) resistance under working load condition
Ap = area of pile cross section
Ep = modulus of elasticity of the pile material
L = length of pile
 = the magnitude which depend on the nature of unit friction (skin) resistance distribution along the pile shaft.

5. SETTLEMENT OF PILES Where:
qwp = point load per unit area at the pile point = Qwp/Ap
D = width or diameter of pile
Es = modulus of elasticity of soil at or below the pile point
s = poisson’s ratio of soil
Iwp = influence factor
= r

6. SETTLEMENT OF PILES Where: Qws = friction resistance of pile
L = embedment length of pile
p = perimeter of the pile
Iws = influence factor

7. EXAMPLE
The allowable working load on a prestressed concrete pile 21 m long that has been driven into sand is 502 kN. The pile data are as follow:
- Diameter (D) = 356 mm
The area of cross section (Ap) = 1045 cm2
Perimeter (p) = m
Skin resistance carries 350 kN of the allowable load, and point bearing carries the rest. Use Ep = 21 x 106 kN/m2, Es = 25,000 kN/m2, s = 0.35 and  = 0.62)
Determine the settlement of the pile.

8. EXAMPLE
S = S1 + S2 + S3 = = mm

9. LATERALLY LOADED PILE

10. LATERALLY LOADED PILE
ELASTIC SOLUTION – EMBEDDED IN GRANULAR SOIL

11. LATERALLY LOADED PILE

12. LATERALLY LOADED PILE
For L/T  5

13. LATERALLY LOADED PILE

14. LATERALLY LOADED PILE

15. LATERALLY LOADED PILE
ELASTIC SOLUTION – EMBEDDED IN COHESIVE SOIL

16. LATERALLY LOADED PILE

17. LATERALLY LOADED PILE
ULTIMATE LOAD ANALYSIS – MEYERHOF – PILES IN SAND
ULTIMATE LOAD RESISTANCE (Qu(g))

18. LATERALLY LOADED PILE
MAXIMUM MOMENT, Mmax DUE TO THE LATERAL LOAD Qu(g)
For long (flexible) piles in sand
MAXIMUM MOMENT, Mmax DUE TO THE LATERAL LOAD Qg

19. LATERALLY LOADED PILE
ULTIMATE LOAD ANALYSIS – MEYERHOF – PILES IN CLAY
ULTIMATE LOAD RESISTANCE (Qu(g))

20. LATERALLY LOADED PILE
MAXIMUM MOMENT, Mmax DUE TO THE LATERAL LOAD Qu(g)
For long (flexible) piles
MAXIMUM MOMENT, Mmax DUE TO THE LATERAL LOAD Qg

21. PULL OUT RESISTANCE OF PILES

22. PULL OUT RESISTANCE OF PILES

23. PULL OUT RESISTANCE OF PILES
EXAMPLE:
A concrete pile 50 long is embedded in a saturated clay with cu = 850 lb/ft2. The pile is 12 in. x 12 in. in cross section. Use FS = 4 and determine the allowable pullout capacity of the pile
Solution
Given cu = 850 lb/ft2  kN/m2
’ = 0.9 – cu = 0.9 – ( )(40.73) = 0.645

24. PULL OUT RESISTANCE OF PILES

25. PULL OUT RESISTANCE OF PILES
For dry soils, the equation simplifies to
Determine the value of Ku and  from figure 9.36b and 9.36c.
Where Tun(all) = allowable uplift capacity and FS is Factor of Safety (a value of 2 – 3 is recommended)

26. PULL OUT RESISTANCE OF PILES
EXAMPLE:
a precast concrete pile with a cross section 350 mm x 350 mm is embedded in sand. The length of pile is 15 m. Assume that sand = 15.8 kN/m3, sand = 35o, and the relative density of sand = 70%. Estimate the allowable pullout capacity of the pile (FS = 4)
Solution
From figure 9.36, for  = 35o and relative density = 70%

27. PILE DRIVING FORMULA

28. NEGATIVE SKIN FRICTION
Can occur under condition such as:
If a fill of clay soil is placed over a granular soil layer into which a pile is driven, the fill will gradually consolidate. This consolidation process will exert a downward drag force on the pile during a period of consolidation
If a fill of granular soil is placed over a layer of soft clay. It will induce the process of consolidation in the clay layer and thus exert a downward drag on the pile

29. NEGATIVE SKIN FRICTION
CLAY FILL OVER GRANULAR SOIL

30. NEGATIVE SKIN FRICTION
GRANULAR SOIL FILL OVER CLAY
THE UNIT NEGATIVE SKIN FRICTION AT ANY DEPTH FROM z = 0 TO z = L1

31. NEGATIVE SKIN FRICTION