1. 8. Axial Capacity of Single Piles
CIV4249
©1998 Dr. J.P. Seidel
Modified by J.K. Kodikara, 2001

2. Methods Pile driving formulae Static load test
Dynamic or Statnamic load test
Static formulae

3. Pile driving formulae e.g. Hiley formula (Energy balance) Q = e.W.h .
F (set + tc / 2)
Ru= working load, W=weight of the hammer, h= height of the hammer drop (stroke), F=factor of safety
tc= elastic (temporary) compression
 = efficiency F D s tc Ru

4. Static Load Test Load Deflection What is the failure load?
Plunging failure
Load to specified
contract requirement
Davisson’s Method
Butler and Hoy
Chin’s Method
Brinch Hanson
etc. etc.
What is the distribution
of resistance?
Approximate methods
Instrumentation
Deflection

5. Dynamic and Statnamic Testing Methods
Rapid alternatives to static testing
Cheaper
Separate dynamic resistance
Correlation

6. Pu
Axial Capacity W Qs
Pu = Qb + Qs - W Qb

7. Base Resistance Qb Qb = Ab [cbNc + P’ob(Nq-1) + 0.5gBNg + Pob]
minus weight of pile, Wp
but Wp » Ab.Pob Qb
and as L >>B, 0.5gBNg << Wp
and for f > 0, Nq - 1 » Nq
Qb = Ab [cbNc + P’obNq]

8. Shaft Resistance As Due to cohesion or friction
Cohesive component : Qsc = As . a . cs
Frictional component : Qsf = As .K P’ostan d
P’os
K.P’os
Qs = Qsc + Qsf = As [ a .cs + K P’ostan d ]

9. Total Pile Resistance Qu = Qb + Qs
Qu = Ab [cbNc+P’obNq] + As [ a .cs+K P’otan d ]
How do we compute Qu when shaft resistance along the pile is varying?

10. Mobilization
% diam
2 - 5mm
Load
Total
Base
Shaft
Settlement

11. Piles in Clay Qu = Ab [cbNc+P’obNq] + As [ a .cs+K P’otan d ]
Qu = AbcbNc + Asa .cs
Undrained
Qu = Ab [cbNc+P’obNq] + As [ a .cs+K P’otan d ]
Qu = Ab [cbNc+P’obNq] + As [ a .cs+K P’otan d ]
Qu = Ab P’obNq + AsK P’ostan d
Drained / Effective
Qu = Ab P’obNq + AsK P’otan d
Qu = AbcbNc + Asa .cs

12. Driven Piles in Clay

13. Driven Piles in Clay

14. Nc Parameter Nc Compare Skempton’s Nc for shallow foundations
Nc= 5(1+0.2B/L)(1+0.2D/ B)

15. Adhesion Factor, 
Aust. Piling Code, AS159 (1978)

16. Bored Piles in Clay Skempton’s recommendations for side resistance
 = for cu <215 kPa
cu =100 kPa for cu>215 kPa
Nc is limited to 9.
A reduction factor is applied to account for likely fissuring (I.e., Qb = Ab  cb Nc)

17. Soil disturbance
sampling attempts to establish in-situ strength values
soil is failed/remoulded by driving or drilling
pile installation causes substantial disturbance
bored piles : potential loosening
driven piles : probable densification

18. Scale effects
Laboratory samples or in-situ tests involve small volumes of soil
Failure of soil around piles involves much larger soil volumes
If soil is fissured, the sample may not be representative

19. Piles in Sand Qu = Ab [cbNc+P’obNq] + As [ a .cs+K P’ostan d ]
Qu = Ab P’obNq] + AsK P’ostan d ]

20. Overburden Stress P’ob
Qu = Ab P’obNq] + AsK P’ostan d ]
Meyerhof Method : P’ob = g’z
Vesic Method : critical depth, zc
for z < zc : P’ob = g’z
for z > zc : P’ob = g’zc
zc/d is a function of f after installation
- see graph p. 24

21. Critical Depth (zc)

22. Bearing Factor, Nq Qu = Ab P’obNq] + AsK P’ostan d ]
Nq is a function of :
Nq is a function of :
friction angle, f
Total end bearing may also be limited:
Layered soils :
Nq may be reduced if penetration
insufficient. e.g. Meyerhof (p 21)
What affects f ?
In-situ density
Particle properties
Installation procedure
Meyerhof : Qb < Ab50Nqtanf
Beware if f is pre- or post-installation:
Nq determined from graphs appropriate
to each particular method

23. Nq factor (Berezantzev’s Method)
If D/B <4
reduce proportionately to Terzaghi and Peck values

24. Overburden Stress P’os
Qu = Ab P’obNq] + AsK P’ostan d ]
Meyerhof Method : P’os = g’zmid
Vesic Method : critical depth, zc
for zmid < zc : P’ob = g’z
for zmid > zc : P’ob = g’zc
zc/d is a function of f after installation
- see graph p. 24

25. Lateral stress parameter, K
A function of Ko
normally consolidated or overconsolidated - see Kulhawy properties manual
see recommendations by Das, Kulhawy (p26)
A function of installation
driven piles (full, partial displacement)
bored piles
augercast piles
screwed piles

27. K.tand The K and tand values are often combined into a single function
see p 28 for Vesic values from Poulos and Davis

28. Pile-soil friction angle, d
A function of f
See values by Broms and Kulhawy (p26)
A function of pile material
steel, concrete, timber
A function of pile roughness
precast concrete
Cast-in-place concrete

29. Pile-soil friction angle

30. Example Driven precast concrete pile 350mm square
Uniform dense sand (f = 40o ; g = 21kN/m3)
Water table at 1m
Pile length 15m
Check end bearing with Vesic and Meyerhof Methods
Pile is driven on 2m further into a very dense layer
f = 44o ; g = 21.7 kN/m3
Compute modified capacity using Meyerhof

31. Example Bored pile 900mm diameter
Uniform medium dense sand (f = 35o ; g = 19.5kN/m3)
Water table at 1m
Pile length 20m
Check shaft capacity with Vesic and Meyerhof Methods
By comparsion, check capacity of 550mm diameter screwed pile

32. Lateral load on single pile
Calculation of ultimate lateral resistance (refer website/handouts for details)
Lateral pile deflection (use use subgrade reaction method, p-y analysis)
Rock socketed pile (use rocket, Carter et al method)