DESIGN ANDANALYSIS OF DEEP FOUNDATION

concretecakeUrban and Civil

Nov 29, 2013 (3 years and 11 months ago)

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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.