1. Session 25 – 26 DRILLED SHAFT And CAISSON FOUNDATION
Course : S0484/Foundation Engineering
Year : 2007
Version : 1/0
Session 25 – 26 DRILLED SHAFT And CAISSON FOUNDATION

2. DRILLED SHAFT And CAISSON FOUNDATION
Topic:
Types of Drilled Shaft
Design Method of Drilled Shaft
Installation Method of Drilled Shaft
Types of Caisson Foundation
Design Method of Caisson Foundation

3. TYPES OF DRILLED SHAFT

4. DESIGN METHOD OF DRILLED SHAFT
ESTIMATION OF LOAD BEARING CAPACITY - GENERAL
Where:
Qu = ultimate load
Qp = ultimate load-carrying capacity at the base
Qs = frictional (skin) resistance

5. DESIGN METHOD OF DRILLED SHAFT
Ultimate Base Load
(In most cases, the third term is neglected)
Net load-carrying capacity at the base
Where:
Nc*, Nq*, N* = the bearing capacity factor
q’ = vertical effective stress at the level of the bottom of pier
Db = diameter of the base
Ap = area of the base = /4 . Db2

6. DESIGN METHOD OF DRILLED SHAFT
Friction or Skin resistance, Qs
Where:
p = shaft perimeter = .Ds
f = unit frictional (skin) resistance

7. DESIGN METHOD OF DRILLED SHAFT - SAND
Net load-carrying capacity at the base
Friction or Skin resistance
Where:
p = shaft perimeter = .Ds
f = unit frictional (skin) resistance = K.v’.tan
K = earth pressure coefficient  Ko = 1 - sin
v’ = effective vertical stress at any depth z
Net allowable load

8. DESIGN METHOD OF DRILLED SHAFT - CLAY
Net load-carrying capacity at the base
Friction or Skin resistance
Where:
cu = undrained cohesion
Nc* = bearing capacity factor = 9
p = perimeter of the shaft cross section
* = varies between 0.3 to 1.0 or

9. SETTLEMENT OF DRILLED SHAFT AT WORKING LOAD
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

10. SETTLEMENT OF DRILLED SHAFT AT WORKING LOAD
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.

11. SETTLEMENT OF DRILLED SHAFT AT WORKING LOAD
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

12. SETTLEMENT OF DRILLED SHAFT AT WORKING LOAD
Where:
Qws = friction resistance of pile
L = embedment length of pile
p = perimeter of the pile
Iws = influence factor

13. UPLIFT CAPACITY OF DRILLED SHAFT

14. UPLIFT CAPACITY OF DRILLED SHAFT
NET ULTIMATE UPLIFT CAPACITY OF DRILLED SHAFT IN SAND

15. UPLIFT CAPACITY OF DRILLED SHAFT

16. UPLIFT CAPACITY OF DRILLED SHAFT

17. UPLIFT CAPACITY OF DRILLED SHAFT
NET ULTIMATE UPLIFT CAPACITY OF DRILLED SHAFT IN SAND
Determine L, Db, and L/Db
Estimate (L/Db)cr and hence Lcr
If (L/Db)  (L/Db)cr, obtain Bq from the graph and
4. If (L/Db) >(L/Db)cr
Frictional resistance developed along the soil-shaft interface from z = 0 to z = L – Lcr and is similar to:

18. UPLIFT CAPACITY OF DRILLED SHAFT

19. UPLIFT CAPACITY OF DRILLED SHAFT
NET ULTIMATE UPLIFT CAPACITY OF DRILLED SHAFT IN CLAY

20. UPLIFT CAPACITY OF DRILLED SHAFT

21. UPLIFT CAPACITY OF DRILLED SHAFT
NET ULTIMATE UPLIFT CAPACITY OF DRILLED SHAFT IN CLAY
Determine cu, L, Db, and L/Db
Estimate (L/Db)cr and obtain Lcr
If (L/Db)  (L/Db)cr, obtain Bc from the graph and
4. If (L/Db) >(L/Db)cr, Bc = 9 and

22. UPLIFT CAPACITY OF DRILLED SHAFT
The skin resistance obtained from the adhesion along the soil-shaft interface and is similar to
With

23. DRILLED SHAFT INSTALLATION

24. DRILLED SHAFT INSTALLATION

25. TYPES OF CAISSONS

26. TYPES OF CAISSONS

27. DESIGN METHOD OF CAISSONS FOUNDATION
THICKNESS OF CONCRETE SEAL IN OPEN CAISSONS
(b). Rectangular Caisson Lo Bo Bi Li

28. DESIGN METHOD OF CAISSONS FOUNDATION
TWO OTHER CONDITIONS SHOULD BE CHECKED FOR SAFETY:
1. Check for Perimeter Shear at Contact Face of Seal and Shaft
The Perimeter shear, , should be less than the permissible shear stress, u

29. DESIGN METHOD OF CAISSONS FOUNDATION
TWO OTHER CONDITIONS SHOULD BE CHECKED FOR SAFETY:
2. Check for Buoyancy
If the shaft is completely dewatered, the bouyant upward, Fu is
The downward force, Fd, is caused by the weight of the caisson and the seal and by the skin friction at the caisson-soil interface
If Fd > Fu  the caisson is safe from bouyancy
If Fd < Fu  dewatering the shaft completely will be unsafe and the thickness of the seal should be increased by t, or