DESIGN AND
ANALYSIS OF DEEP FOUNDATION
WEEK 9
•
FRICTION AND END BEARING PILES
•
BEARING CAPACITY ANALYSIS OF PILES USING
EMPIRICAL AND DYNAMIC FORMULAE
Learning Outcomes
Student should be able to:
•
Explain the end bearing and skin friction
contribution to pile capacity.
•
Estimate the bearing capacity of a pile.
DESIGN AND ANALYSIS OF DEEP FOUNDATION
END BEARING PILES
FRICTION PILES
IN GENERAL MOST PILES HAVE END BEARING
AND SKIN FRICTION RESISTANCE
SUBSOIL CONDITIONS DETERMINE THE CATEGORY
OF PILE
PILE CLASSIFICATION BASED ON BEARING CAPACITY:
DESIGN CONSIDERATION OF DEEP FOUNDATION
GEOTECHNICAL ENGINEERING IS A BRANCH OF
CIVIL ENGINEERING WHICH REQUIRES THE MOST
OF EXPERIENCE AND JUDGEMENT OF ITS
PRACTITIONER
For example, it is prudent to design micropile using skin
Friction only if its in a limestone karstic formation due to
Presence of cavities and overhang
Some designers ignore end bearing contribution for bored
When in doubt that the base will be properly cleaned
To produce satisfactory pile foundation systems that are
Neither unnecessarily over

designed or dangerously
inadequate
Pile Design
Concept
Friction Pile
End Bearing Pile
Summary of Pile Capacity Calculation
Not more 100kPa
Factor of Safety for Design
FOS for skin friction is 2
FOS for end bearing resistance is 3
Generally design the working load of the pile to be
Around 80% of geotechnical capacity
TENSION PILE
Piles that are designed to take uplifting load due to:
Wind eg a hangar
Tall chimneys (overturning)
Transmission towers
Jetty structures
Skin frictional resistance is much lower than those for compression
50% reduction is suggested
Pull out test may be conducted
Lateral force eg wave action if transmitted to pile will
Destroy most of the skin friction.
Factor of Safety to be applied ie FOS = 2
Tension pile has no end bearing resistance.
To be designed for both compression and tension loads.
WAVE EQUATION
Pile Capacity

Static Analysis

Dynamic Analysis

Dynamic formulae

Wave Equation
Dynamic Formulae

Engineering New formula

Hiley
Main weakness

modeling of the pile as one rigid mass
inadequate modeling of soil
–
pile interaction
History of Wave Equation Method
David Victor Issacs (1931)
In Australia. He reviewed the Dynamic Formulae.
Developed mathematical model based on successive
Transmission and reflection of waves.
Glanville et. Al (1938)
Problem of concrete pile breakages at top and toe during driving.
Wave equation was used to estimate stress in pile.
Charts were developed for usage but applicable only to concrete
Piles.
Smith (1960)
Numerical method.

Division of piles into springs and masses. Hammer modeled as mass
With cushion spring.

Integration of model using finite difference technique.

Modeling of soil as combination of displacement dependent springs
And velocity dependent dampers. Applied along the pile shaft
They modeled the soil resistance.

Modeling of the non

linearities of soil. The soil was given a
‘yield limit’ (quake);a after this time the non

dynamic resistance
Resistance was constant.
The Pile

Soil Model
Standard model used in many wave equation techniques today
Goble et. Al (1980)
Major steps in using stress wave theory to piles during driving
And to estimate static capacity by Case Method.
Compare pile force and velocity at a given time with a time
2L/c before that .
The static and dynamic components separated.
Field application using strain gauge to measure force and
Accelerometer to measure velocity.
Rausche et. al (1985)
CAPWAP technique (Case Pile Wave Analysis Program)
Similar instrumentation to Case Method but pile is divided into
Series of elements and the wave reflection for each one are
Analysed based on the time return to the top of pile.
A profile of shaft resistance distribution is obtained.
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