1
30 May 2008 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
1
Pile Foundation Concepts and Design
Main / Skirt PilePile Group ArrangementVertical Axial Soil CapacityStructural Capacity
CONTENTS
30 May 2008 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
2
Pile Foundation Concepts and Design
Pile Simulation for an Offshore Jacket
2
30 May 2008 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
3
Pile Foundation Concepts and Design
Pile group arrangements for 4 legged platform
30 May 2008 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
4
Pile Foundation Concepts and Design
Pile group arrangements for 4 legged platform
3
30 May 2008 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
5
Pile Foundation Concepts and Design
Pile group arrangements for 8 legged platform
30 May 2008 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
6
Pile Foundation Concepts and Design
Pile group arrangements for 8 legged platform
4
30 May 2008 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
7
Pile Foundation Concepts and Design
Ultimate Bearing Capacity The ultimate bearing capacity of pile, including
belled piles, Qd should be determined by the equation.
Qd= Qf+Qp=fAs+qAp
WhereQf=skin friction resistance, Ib (kN)Qp= total end bearing, Ib (kN),f = unit skin friction capacity, Ib/ft2 (kPa)As = side surface area of pile, ft2 (m2),Ap = gross end area of pile, ft2 (m2),
30 May 2008 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
8
Pile Foundation Concepts and Design
Where α = a dimensionless factor,c = un-drained shear strength of the soil at the point in
questionThe factor, α, can be computed by the equations:α = 0.5 Ψ-0.5 Ψ≤1.0α = 0.5 Ψ-0.25 Ψ >1.0With the constraint that, α ≤ 1.0,Where Ψ = c/p’0 for the point in question c/p’0 effective overburden pressure at the point in question Ib/ft2 (kPa)
5
30 May 2008 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
9
Pile Foundation Concepts and Design
For piles end bearing in cohesive soils, the unit end bearing q.in Ibs/ft2
(kPa), may be computed by the equation
q = 9c
Cohesive Soil
30 May 2008 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
10
Pile Foundation Concepts and Design
Cohesionless SoilsFor pipe piles in cohesionless soils, the shaft friction, f. in Ib/ft2 (kPa) may be calculated by the equation:
f = Kpao tan δWhere K = coefficient of lateral earth pressure (ratio of
horizontal to vertical normal effective stress)po = effective overburden pressure Ib/ft2 (kPa) at the point
in questionδ = friction angle between the soil and pile wall
6
30 May 2008 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
11
Pile Foundation Concepts and Design
For pipe piles in cohesionless oils, the unit shaft friction at a given depth, f, may be calculated by the equation
f = βp´0
β = dimensionless shaft friction factorp´0 = effective overburden pressure at
the depth in question
30 May 2008 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
12
Pile Foundation Concepts and Design
For piles end bearing in cohesionlesssoils, the unit and bearing q may be computed by the equation
q=Nqp´0
WhereNq=dimensionless bearing capacity
factorp´0 = effective overburden pressure at
the depth in question
7
30 May 2008 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
13
Pile Foundation Concepts and Designold
API 2A
Recommended Practice
30 May 2008 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
14
Pile Foundation Concepts and DesignNew
API 2A
Recommended Practice
8
30 May 2008 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
15
Pile Foundation Concepts and Design
t-z curve for deformation of a pile under vertical axial loading
30 May 2008 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
16
Pile Foundation Concepts and Design
Where
z = local pile deflection, in. (mm),
D = pile diameter, in. (mm).
t = mobilized soil pile adhesion, Ib/ft2 (kPa)
tmax = maximum soil pile adhesion or unit skin friction capacity computed accoringto Section 6.4. Ib/ft2 (kPa)
9
30 May 2008 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
17
Pile Foundation Concepts and DesignTypical Axial Pile Load Transfer-Displacement (t-z) Curves
30 May 2008 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
18
Pile Foundation Concepts and Design
Tip-load – Displacement Curve
Where
z = axial tip deflection, in. (mm),
D = pile diameter, in. (mm).
Q = mobilized end bearing capacity, Ib(KN)
Qp = total end bearing, Ib(KN), computed according to section 6.4
10
30 May 2008 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
19
Pile Foundation Concepts and Design
Pile tip load – Displacement (Q-z) curve
30 May 2008 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
20
Pile Foundation Concepts and Design
STRUCTURAL DESIGN ISSUES
Design for structural strength to resistAxial forceLateral shear forceBending moment
Make allowance for corrosion / durabilityConsider possibility of buckling
Only likely to be of concern for slender piles in very soft clay with unsupported length
11
30 May 2008 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
21
Pile Foundation Concepts and Design
PILE BUCKLINGReplace pile by
equivalent cantilever
CRITICAL LOAD is
k) increasing(linearly )J4(SIE.
P
k)constant ()J4(S
IE. P
22RR
pp2
cr
2RR
pp2
cr
R+=
+=
π
π
30 May 2008 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
22
Pile Foundation Concepts and Design
PILE BUCKLING
12
30 May 2008 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
23
Pile Foundation Concepts and Design
DURABILITY ISSUESCOUNTER MEASURES FOR STEEL PILES(COASTAL STRUCTURES)
Corrosion protection paintPolyethylene cover (steel pipes)Zinc coating Electro – chemical (cathodic) protection Cement or concrete cover