P

ile Foundation Design: A Student Guide

Ascalew Abebe & Dr Ian GN Smith
School of the Built Environment, Napier University, Edinburgh
See Elements of Soil Mechanics (8th Edition) to learn how to design piles
(and other geotechnical structures) to Eurocode 7. Full details are
here....
(Note: This Student Guide is intended as just that
- a guide for students of civil engineering. Use it
as you see fit, but please note that there is no
technical support available to answer any
questions about the guide!)
PURPOSE OF TE GUIDE
There are many tets on pile foundations.
!enerally, eperience shows us that
undergraduates find most of these tets
complicated and difficult to understand.
This guide has etracted the main points and


puts together the whole process of pile
foundation design in a student friendly
manner.
The guide is presented in two versions" tet-
version #compendium from) and this web-
version that can be accessed via internet or
intranet and can be used as a supplementary
self-assisting students guide.
STRUCTURE OF THE GUIDE
Intro!"ction to #ile $o"n!ations
Pile $o"n!ation !esi%n
&oa! on #iles
Sin%le #ile !esi%n
Pile %ro"# !esi%n
Installation'test'an! $actor o$ sa$et(
Pile installation metho!s
Test #iles
Factors o$ sa$et(
Pile Foundation Design: A Student Guide
)ha#ter * Intro!"ction to #ile $o"n!ations
$.$ %ile foundations
$.& 'istorical
$.( )unction of piles
$.* +lassification of piles
1.4.1 lassification of pile !ith respect to load transmission and functional behaviour
1.4." End bearing piles
1.4.# $riction or cohesion piles
1.4.4 ohesion piles
1.4.% $riction piles
1.4.& ombination of friction piles and cohesion piles
1.4.' .lassification of pile !ith respect to type of material
1.4.( )imber piles
1.4.* oncrete pile
1.4.1+ ,riven and cast in place oncrete piles
1.4.11 Steel piles
1.4.1" omposite piles
1.4.1# lassification of pile !ith respect to effect on the soil
1.4.14 ,riven piles
1.4.1% Bored piles
$., -ide to classification of piles
$.. -dvantages and disadvantages of different pile material
$./ +lassification of piles - 0eview
)ha#ter + &oa! on #iles
&.$ 1ntroduction
&.& %ile arrangement
)ha#ter , &oa! Distrib"tion
(.$ %ile foundations" vertical piles only
(.& %ile foundations" vertical and ra2ing piles
(.( 3ymmetrically arranged vertical and ra2ing piles
#.#.1 E-ample on installation error
)ha#ter - &oa! on Sin%le Pile
*.$ 1ntroduction
*.& The behaviour of piles under load
*.( !eotechnical design methods
4.#.1 )he undrained load capacity .total stress approach/
4.#." ,rained load capacity .effective stress approach/
4.#.# 0ile in sand
*.* 4ynamic approach
)ha#ter . Sin%le Pile Desi%n
,.$ 5nd bearing piles
,.& )riction piles
,.( +ohesion piles
,.* 3teel piles
,., +oncrete piles
,.,.$ %re-cast concrete piles
,.. Timber piles #wood piles)
%.&.1 Simplified method of predicting the bearing capacity of timber piles
)ha#ter / Desi%n o$ Pile Gro"#
..$ 6earing capacity of pile groups
&.1.1 0ile group in cohesive soil
&.1." 0ile groups in non1cohesive soil
&.1.# 0ile groups in sand
)ha#ter 0 Pile S#acin% an! Pile Arran%ement

)ha#ter 1 Pile Installation 2etho!s
7.$ 1ntroduction
7.& %ile driving methods #displacement piles)
(.".1 ,rop hammers
(."." ,iesel hammers
(.".# 0ile driving by vibrating
7.( 6oring methods #non-displacement piles)
(.#.1 ontinuous $light 2uger .$2/
(.#." Underreaming
(.#.# .3.0
)ha#ter 3 &oa! Tests on Piles
8.$ 1ntroduction
*.1.1 40 .constant rate of penetration/
*.1." 56), the maintained increment load test
)ha#ter *4 &imit State Desi%n
$9.$ !eotechnical category !+ $
$9.& !eotechnical category !+ &
$9.( !eotechnical category !+ (
1+.#.1 onditions classified as in Eurocode '
$9.* The partial factors m, n, 0d
Pile Foundation Design: A Student Guide
Introduction to pile foundations
Objectives: Texts dealing with geotechnical and
ground engineering techniques classify piles in a
number of ways. The objective of this unit is that
in order to help the undergraduate student
understand these classifications using materials
extracted from several sources, this chapter
gives an introduction to pile foundations.
! "ile foundations
Pile foundations are the part of a structure used
to carry and transfer the load of the structure to
the bearing ground located at some depth below
ground surface. The main components of the
foundation are the pile cap and the piles. Piles
are long and slender members which transfer the
load to deeper soil or rock of high bearing
capacity avoiding shallow soil of low bearing
capacity The main types of materials used for
piles are Wood, steel and concrete. Piles made
from these materials are driven, drilled or jacked
into the ground and connected to pile caps.
epending upon type of soil, pile material and
load transmitting characteristic piles are
classified accordingly. !n the following chapter we
learn about, classifications, functions and pros
and cons of piles.
!# Historical
Pile foundations have been used as load carrying
and load transferring systems for many years.
!n the early days of civilisation"#$, from the
communication, defence or strategic point of
view villages and towns were situated near to
rivers and lakes. !t was therefore important to
strengthen the bearing ground with some form of
piling.
Timber piles were driven in to the ground by
hand or holes were dug and filled with sand and
stones.
!n %&'( )hristoffoer Polhem invented pile driving
equipment which resembled to days pile driving
mechanism. *teel piles have been used since
%+(( and concrete piles since about %,((.
The industrial revolution brought about important
changes to pile driving system through the
invention of steam and diesel driven machines.
-ore recently, the growing need for housing and
construction has forced authorities and
development agencies to exploit lands with poor
soil characteristics. This has led to the
development and improved piles and pile driving
systems. Today there are many advanced
techniques of pile installation.
!$ Function of piles
.s with other types of foundations, the purpose
of a pile foundations is/
to transmit a foundation load to a solid ground
to resist vertical, lateral and uplift load
. structure can be founded on piles if the soil
immediately beneath its base does not have
adequate bearing capacity. !f the results of site
investigation show that the shallow soil is
unstable and weak or if the magnitude of the
estimated settlement is not acceptable a pile
foundation may become considered. 0urther, a
cost estimate may indicate that a pile foundation
may be cheaper than any other compared
ground improvement costs.
!n the cases of heavy constructions, it is likely
that the bearing capacity of the shallow soil will
not be satisfactory, and the construction should
be built on
pile foundations. Piles can also be used in
normal ground conditions to resist hori1ontal
loads. Piles are a convenient method of
Pile Foundation Design: A Student Guide
%O&D O'
"I%ES
#! Introduction
This section of the guide is divided into
two parts. The first part gives brief
summary on basic pile arrangements
while part two deals with load
distribution on individual piles.
Piles can be arranged in a number of
ways so that they can support load
imposed on them. 2ertical piles can be
designed to carry vertical loads as well
as lateral loads. !f required, vertical
piles can be combined with raking
piles to support hori1ontal and vertical
forces.
often, if a pile group is subjected to
vertical force, then the calculation of
load distribution on single pile that is
member of the group is assumed to be
the total load divided by the number of
piles in the group. 3owever if a group
of piles is subjected to lateral load or
eccentric vertical load or combination
of vertical and lateral load which can
cause moment force on the group
which should be taken into account
during calculation of load distribution.
!n the second part of this section, piles
are considered to be part of the
structure and force distribution on
individual piles is calculated
accordingly.

Objective/ !n the first part of this
section, considering group of piles with
limited number of piles subjected to
vertical and lateral forces, forces
acting centrally or eccentrically, we
learn how these forces are distributed
on individual piles.
The worked examples are intended to
give easy follow through exercise that
can help quick understanding of pile
design both single and group of piles.
!n the second part, the comparison
made between different methods used
in pile design will enable students to
appreciate the theoretical background
of the methods while exercising pile
designing.
%earnin( outco)e
When students complete this section,
they will be able to/
)alculate load
distribution on group
of piles consist of
vertical piles
subjected to eccentric
vertical load.
)alculate load
distribution on
vertically arranged
piles subjected to
lateral and vertical
forces.
)alculate load
distribution on vertical
and raking piles
subjected to hori1ontal
and eccentric vertical
loads.
)alculate load
distribution on
symmetrically
arranged vertical and
raking piles subjected
to vertical and lateral
forces

#!# "ile arran(e)ent
4ormally, pile foundations consist of
pile cap and a group of piles. The pile
cap distributes the applied load to the
individual piles which, in turn,. transfer
the load to the bearing ground. The
individual piles are spaced and
connected to the pile cap or tie beams
and trimmed in order to connect the
pile to the structure at cut-off level,
and depending on the type of structure
and eccentricity of the load, they can
be arranged in different patterns.
0igure #.% bellow illustrates the three
basic formation of pile groups.

a5 P!67 89:;P ):4*!*T :0 :46< b5 P!67 89:;P ):4*!*T :0 =:T3
279T!).6 .4 9.>!48 P!67*

0igure #?% =asic formation of pile groups
Pile Foundation Design: A Student Guide
%O&D
DISTRI*UTIO
'
To a great extent the
design and calculation
@load analysis5 of pile
foundations is carried out
using computer software.
0or some special cases,
calculations can be carried
out using the following
methodsA...0or a simple
understanding of the
method, let us assume that
the following conditions are
satisfied/
The pile is rigid
The pile is pinned at the
top and at the bottom
7ach pile receives the load
only vertically @i.e. axially
applied 5B
The force P acting on the
pile is proportional to the
displacement ; due to
compression
0 7 8.U
Since 0 7 E.2
E.2 7 8.U

where:
P

= vertical load component
k = material constant
U = displacement
E = elastic module of pile
material
A = cross-sectional area of
pile
0igure C?% load on single pile
The length 6 should not
necessarily be equal to the actual
length of the pile. !n a group of
piles, !f all piles are of the same
material, have same cross?
sectional area and equal length 6 ,
then the value of k is the same for
all piles in the group.
6et us assume that the vertical
Pile Foundation Design: A Student Guide
%O&D O'
SI'G%E "I%E
+! Introduction
!n this section, considering pileDsoil
interaction, we learn to calculate the
bearing capacity of single piles
subjected to compressive axial load.
uring pile design, the following
factors should be taken into
consideration/
deformation area of pile, bending moment capacity
condition of the pile at the top and the end of the pile
eccentricity of the load applied on the pile
soil characteristics
ground water level ..etc.

4evertheless, calculation method
that can satisfy all of these
conditions will be complicated and
difficult to carry out manually,
instead two widely used simplified
methods are presented. These two
methods are refereed as
geotechnical and dynamic methods.
This section too has worked
examples showing the application of
the formulae used in predicting the
bearing capacity of piles made of
different types of materials.
%earnin( outco)e
When students complete this
section, they will be able to
understand the theoretical
back ground of the formulae
used in pile design
carry out calculation and be
able to predict design
bearing capacity of single
piles
appreciate results calculated
by means of different
formulae

+!# T,e be,aviour of piles under
load
Piles are designed that calculations
and prediction of carrying capacity is
based on the application of ultimate
axial load in the particular soil
conditions at the site at relatively
short time after installation.
This ultimate load capacity can be
determined by either/
the use of empirical formula to
predict capacity from soil
properties determined by
testing, or
load test on piles at the site
0ig.'?%, When pile is subjected to
gradually increasing compressive
load in maintained load stages,
initially the pile?soil system behaves
in a linear?elastic manner up to point
. on the settlement?load diagram
and if the load is realised at any
stage up to this point the pile head
rebound to its original level. When
the load is increase beyond point .
?

there is yielding at, or close to, the
pile?soil interface and slippage
occurs until point =
?
is reached,
when the maximum skin friction on
the pile shaft will have been
mobilised. !f the load is realised at
this stage the pile head will rebound
to point )
?
, the amount of
permanent settlement being the
distance :). When the stage of full
mobilisation of the base resistance
is reached @ point 5, the pile
plunges downwards with out any
farther increase of load, or small
increases in load producing large
settlements.
?
:o end-bearing is mobilised up to this
point. The whole of the load is carried
by the s2in friction on the pile shaft see
figure 4-1 I)
?
The pile shaft is carrying its maimum
s2in friction and the pile toe will be
carrying some load
?
-t this point there is no further increase
in the load transferred in s2in friction
but the base load will have reached its
maimum value.
0igure ?% axial compression of pile

+!$ Geotec,nical desi(n
)et,ods
!n order to separate their
behavioural responses to
applied pile load, soils are
classified as either
granularDnoncohesive or
claysDcohesive. The generic
formulae used to predict soil
resistance to pile load include
empirical modifying factors
which can be adjusted
according to previous
engineering experience of the
influence on the accuracy of
predictions of changes in soil
type and other factors such as
the time delay before load
testing.
@0ig '?$115 the load settlement
response is composed of two
separate components, the
linear elastic shaft friction 9
s

and non?linear base
resistance 9
b
. The concept of
the separate evaluation of
shaft friction and base
resistance forms the bases of
Estatic or soil mechanicsE
calculation of pile carrying
capacity. The basic equations
to be used for this are written
as/
F G F
b
H F
s
? W
p
or
9
c
G 9
b
H 9
s
? W
p
9
t
G 9
s
H W
p

9here: F G 9
c
G the ultimate
compression resistance of the
pile
F
b
G 9
b
G base resistance
F
s
G 9
s
G shaft resistance
W
p
G weight of the pile
9
t
G tensile resistance of pile
!n terms of soil mechanics
theory, the ultimate skin
friction on the pile shaft is
related to the hori1ontal
effective stress acting on the
shaft and the effective
remoulded angle of friction
between the pile and the clay
and the ultimate shaft
resistance 9
s
can be
evaluated by integration of the
pile?soil shear strength
a

over the surface area of the
shaft/
a 7 a ;
n <=o
tan a
9here:
n
7 >
s <=o
:
v

.refer geotechnical
notes/

a
7
a
; >
S
<=o :
v <=o
tan
a
and
!here: p 7 pile perimeter
6 7 pile length
7 angle of friction bet!een pile
and soil
>
s
7 coefficient of lateral
pressure
the ultimate bearing capacity, 4b, of the
base is evaluated from the bearing
capacity theory:
2b 7 area of pile base
7 undrained strength of soil at base
of pile
N 7 bearing capacity factor


Nevertheless, in practise, for a given
pile at a given site, the undrained
shear strength Ca varies
consideral! with man! factors,
including, pile t!pe, soil t!pe, and
methods of installations"
#deall!, Ca should e determined
from a pile-load test, ut since this is
not alwa!s possile, Ca is correlated
with the undrained cohesion Cu !
empirical adhesion factor so that
the general e$pression in e"%" &'-()
could e simplified to the following
e$pression:
*here: *s = weight of soil replaced
! the pile
=average value of shear strength
over the whole shaft length
4.3.1 The undrained load capacity
(total stress approach)
+or piles in cla!, the undrained load
capacit! is generall! taken to e the
critical value unless the cla! is
highl! over consolidated" #f the
undrained or short-term ultimate
load capacit! is to e computed, the
soil parameters C, , , should e
appropriate to undrained conditions
and v and v should e the total
stresses" #f the cla! is saturated
?
,
the undrained angle of friction u is
,ero, and a &angle of friction
etween pile and soil) ma! also e
taken as ,ero" #n addition, N% = (, N
= (, so that the e% in&'-() reduces
to:
*here: Nc, N%, N ,= earing
capacit! factors and are functions of
the internal angle of friction of the
soil, the relative compressiilit! of
the soil and the pile geometr!"
4.3.2 Drained load capacity
(effective stress approach)
+or piles installed in stiff, over
consolidated cla!s, the drained load
capacit! is taken as design criterion"
#f the simplified assumption is made
that the drained pile-soil adhesion
C- a is ,ero and that the term in e%
&'-().involving Nc, N ignoring the
drained ultimate earing capacit! of
the pile ma! e e$pressed as :
*here: s - v, and s - v = effective
vertical stress at depth , respective
at pile ase
f - a,= effective angle of friction
etween pile/soil and implied can e
taken as f - ,
N% which is dependant up on the
values of f - ma! e taken to e the
same as for piles in sand, and can
e decided using tale (0-1 2 (0-3
4.3.3 Pile in sand
#f the pile soil adhesion Ca and term
Nc are taken as ,ero in e"% &'-().
and the terms 0"1 d N is neglected
as eing small in relation to the term
involving N , the ultimate load
capacit! of a single pile in sand ma!
e e$pressed as follows:
*here: s - v, and s - v = effective
vertical stress at depth , respective
at pile ase
+w = correction factor for tapered
pile & = ( for uniform diameter)
4.4 Dynamic approach
4ost fre%uentl! used method of
estimating the load capacit! of
driven piles is to use a driving
formula or d!namic formula" All such
formulae relate ultimate load
capacit! to pile set &the vertical
movement per low of the driving
hammer) and assume that the
driving resistance is e%ual to the
load capacit! to the pile under static
loading the! are ased on an
idealised representation of the
action of the hammer on the pile in
the last stage of its emedment"
Usuall!, pile-driving formulae are
used either to estalish a safe
working load

or to determine the
driving re%uirements for a re%uired
working load"
5he working load is usuall!
determined ! appl!ing a suitale
safet! factor to the ultimate load
calculated ! the formula" 6owever,
the use of d!namic formula is highl!
criticised in some pile-design
literatures" 7!namic methods do not
take into account the ph!sical
characteristics of the soil" 5his can
lead to dangerous miss-
interpretation of the results of
d!namic formula calculation since
the! represent conditions at the time
of driving" 5he! do not take in to
account the soil conditions which
affect the long- term carr!ing
capacit!, reconsolidation, negative
skin friction and group effects"

specified load acting on the

head of the pile


Pile Foundation Design: A Student Guide
SI'G%E "I%E
DESIG'
-! End bearin( piles
!f a pile is installed in a soil with low
bearing capacity but resting on soil
beneath with high bearing capacity,
most of the load is carried by the end
bearing.
!n some cases where piles are driven
in to the ground using hammer, pile
capacity can be estimated by
calculating the transfer of potential
energy into dynamic energy . When
the hammer is lifted and thrown down,
with some energy lose while driving
the pile, potential energy is transferred
into dynamic energy. !n the final stage
of the pileIs embedment,:n the bases
of rate of settlement, it is able to
calculate the design capacity of the
pile.
0or standard pile driving hammers and
some standard piles with load capacity
&+8sp,), the working load for the pile can
be determined using the relationship
between bearing capacity of the pile,
the design load capacity of the pile
described by/ +8sp ? n <=.eq_ +9d and
table J?%
where: +9d G design load for end
baring.
The data is valid only if at the final
stage, rate of settlement is %( mm per
ten blow. .nd pile length not more
than #( m and geo?category # . for
piles with length #( ? C( m respective
C( ? J( m the bearing capacity should
be reduced by %( res. #JK.

Table -. *arin( capacit/ of piles installed b/

,a))erin(
hammer
DROP
A22ER
(release! b(
tri%%er5
!ro# hammer (acti6ate! b( ro#e an! $riction winch

cross'sectional area o$ #ile

$all hei%ht 9.9,,m
&
( T;: 9.( *&9 7N
9.*
9.,
*89
,.9
* T;:
9.(
9.*
9.,
*/9
,*9
.$9
, T;:
9.(
9.*
9.,
,79
./9
/.9

E0a)ple -!
. concrete pile with length #L m and
cross?sectional area @#CJ5<=.eq_
@#CJ5 is subjected to a vertical loading
of C,( k4 @ultimate5 load. etermine
appropriate condition to halt
hammering. Type of hammer rop
hammer activated by rope and friction
winch. )lass #, 8) #, pile length #( m

solution:

= 1.1 ( 103)
vertical load C,( k4 <=.eq_
_:<>?@A@B C=CA DDD > q__|x_
Pile cross?sectional area <=.eq_
(.#CJ
#
G (.(JJ m
#
<=.eq_
type of hammer/ rop hammer
activated by rope and friction winch
<=.eq_

111For piles #2) . $2) len(t,3 t,e

bearin( capacit/ s,ould be reduced
b/ 24
Table value @table J?%5/ 3ammer
weight G ' ton <=.eq_ fall height
(.'Jm @interpolation5
3ammer weight G C ton <=.eq_ fall
height (.J' m
' ton hammer with fall height (.'Jm is
an appropriate choice.

-!# Friction piles

6oad on piles that are driven into
friction material, for the most part the
weight is carried by friction between
the soil and the pile shaft. 3owever
considerable additional support is
obtained form the bottom part.
!n designing piles driven into friction
material, the following formulas can be
used
where" q
ci
E consolidation
resistance
F can be decided using table $9-*
-
b
E end cross-sectional area of the
pile
-
mi
E shaft area of the pile in
contact with the soil.
should be ? $., for piles in friction
material
q
cs
E end resistance at the bottom of
the pile within *
<= > > > .eq_oo.ooo_x.x
> > > > > eo_oq.e._ooo
0igure J?% 0riction Pile

E0a)ple -!#
Pile length ## m, steel pile,
friction pile, external diameter
%(( mm, 8)#,
etermine the ultimate bearing
capacity of the pile

solution/
?
c
@?
m. depth measured from ground
level to bottom of pile/
50a
9
m
- ,
m
,.*
, - $$ ..*
$$ - $7 /.9
$7 - && /.,
&&
m
7.9

The values are slightly
scattered then the usual while
the rest of the condition is
favourable.

4d
E $., #the lowest value)

n
E $.$

.t the base where condition is
unfavourable we get /

s
E 9.,

m
E 9.99&,

esign bearing capacity of the
pile is L# >4.

-!$ Co,esion piles
Piles installed in clay/ The load
is carried by cohesion between
the soil and the pile shaft.
=earing capacity of the pile can
be calculated using the
following formula for pile
installed in clay.
Where/
a i G adhesion factor for earth layer
cudci G undrained shear strength of clay.
.mi G area of pile shaft in contact with
the soil.
The adhesion factor is taken
as ( for the firs three meters
where it is expected hole room
and fill material or week strata.
0or piles with constant cross?
sectional area the value of
can be taken as %.( and for
piles with uniform cross?
sectional growth the value of
can be taken as %.# .
0igure J?# )ohesion Pile
E0a)ple -!$
%+ m wood pile is installed small
end down in clay. Pile diameter
is %#J mm at the end and %(
mmDm increase in diameter. The
undrained shear strength of the
soil, measured from the pile cut?
off level is/ (?L m G %# kP L?%#
m G %L kPa %#?%+ m G %, kPa.
etermine the ultimate load
capacity of the pile. Pile cut?off
level is %.Jm from the ground
level.
9d
G %.&

0igure J?C 7xample J?C
solution
decide the values for
G ( for the first C.( meters
G %.# for the rest of the soil
layer
divided the pile into C parts
@each L.( m in this case5
calculate .verage diameter at
the middle of each section/
.verage diameter / *ottom
@section5 G (.%#JHC.(<=.eq_
@(.(%5 G (.%J
5iddle @section5 G (.%JJHL
<=.eq_ (.(% G (.#%
Top @section5 G (.#%JH@CH#.#J5
<=.eq_ @(.(%5 G (.#L+
=
;ltimate bearing capacity of
the pile is %%&k4

-!+ Steel piles

=ecause of the relative strength of
steel, steel piles withstand driving
pressure well and are usually very
reliable end bearing members,
although they are found in frequent
use as friction piles as well. The
comment type of steel piles have
rolled H, 6 or circular cross?
section@pipe piles5. Pipe piles are
normally, not necessarily filled with
concrete after driving. Prior to driving
the bottom end of the pipe pile usually
is capped with a flat or a cone?shaped
point welded to the pipe.
*trength, relative ease of splicing and
sometimes economy are some of the
advantages cited in the selection of
steel piles.
The highest draw back of steel piles is
corrosion. )orrosive agents such as
salt, acid, moisture and oxygen are
common enemies of steel. =ecause of
the corrosive effect salt water has on
steel, steel piles have restricted use
for marine installations. !f steel pile is
supported by soil with shear strength
greater than &kPa in its entire length
then the design bearing capacity of the
pile can be calculated using the
following formulas. ;se both of them
and select the lowest value of the two/

Where/ m G correction factor
7*) G elasticity module of steel
! G fibre moment
fyc characteristic strength of steel
. G pile cross?sectional area
)uc G characteristic undrained shear
strength of the soil.


E0a)ple -!+
etermine the design bearing capacity
of a *teel pile of external diameter %((
mm, thickness of %( mm. Treated
against corrosion. pile. )onsider
failure in the pile material. )c of the
soil is %+ kPa, favourable condition. *#
*teel =* #%&#
solution /
n G %.%
m G (.,

7sc G #%( 8pa
for =* #%&# fyc G C#( -Pa
G
G G
The first formula gives us lower value,
therefore, the design bearing capacity
of the pile is (.C -4
!f we consider corrosion of %mmDyear
<=.eq_
G G
-!- Concrete piles
9elatively, in comparable
circumstances, concrete piles have
much more resistance against
corrosive elements that can rust steel
piles or to the effects that causes
decay of wood piles, furthermore
concrete is available in most parts of
the world than steel.
)oncrete piles may be pre?cast or
cast?in place. They may be are
reinforced, pre?stressed or plain.
-!-! "re.cast concrete piles
These are piles which are formed, cast
to specified lengths and shapes and
cured at pre casting stations before
driven in to the ground. epending up
on project type and specification, their
shape and length are regulated at the
prefab site. ;sually they came in
square, octagonal or circular cross?
section. The diameter and the length
of the piles are mostly governed by
handling stresses. !n most cases they
are limited to less than #J m in length
and (.J m in diameter. *ome times it
is required to cut off and splice to
adjust for different length. Where part
of pile is above ground level, the pile
may serve as column.
!f a concrete pile is supported by soil
with undrained shear strength greater
than & -Pa in its entire length, the
following formula can be used in
determining the bearing capacity of
the pile /

Where/ 4
u
G bearing capacity of
the pile, designed as concrete
column
7
sc
G characteristic elasticity
module of concrete
!
c
G fibre moment of the
concrete cross?section ignoring
the reinforcement
)
uc
G characteristic undrained
shear strength of the soil in the
loose part of the soil within a
layer of '.( m

E0a)ple -!-
)oncrete pile @(.#CJ5 <=.eq_
@(.#CJ5 cross?section installed
in clay with characteristic
undrained shear strength of %#
kPa. !n favourable condition.
)J(. etermine design load of
the pile. )onsider failure in the
material.
Solution:


ef
G %.C
l
c
Dh G #(
k
c
G (.L, k G (.#', k
s
G (.L#
f
cc
G CJ.J D@%.J<=.eq_ %.%5 G
#%.J -Pa
f
st
G '%(D@%.%J<=.eq_ %.%5 G
C#' -Pa
7ffective reinforced area/
0
9d
G
m<=.eq_
4
;

m
G (., <=.eq_ 0
9d
G
@(.,5(.&L, G (.L,# -4
0ailure checking using the
second formula/
7
cc
G C' 8Pa
The lowest value is (.LC# -4
<=.eq_ esign capacity
G(.LC -
-!7 Ti)ber piles 89ood piles:
Timber piles are frequently used
as cohesion piles and for pilling
under embankments.
7ssentially timber piles are
made from tree trunks with the
branches and bark removed.
4ormally wood piles are
installed by driving. Typically the
pile has a natural taper with top
cross?section of twice or more
than that of the bottom.
To avoid splitting in the wood,
wood piles are sometimes
driven with steel bands tied at
the top or at the bottom end.
0or wood piles installed in soil
with undrained shear strength
greater than &kPa the following
formula can be used in
predicting the bearing capacity
of the pile/
Where/ G reduced strength of
wood
. G cross?sectional area of the
pile
!f the wood is of sound timber,
@e.g. pinewood or spruce wood
with a diameter M (.%Cm5, then
@reduced strength5 of the pile
can be taken as %%-Pa.
!ncrease in load per section of
pile is found to be proportional
to the diameter of the pile and
shear strength of the soil and
can be decided using the
following formula/

where/ .
m,
G area of pile at each
C.J m section mid point of pile
)
m
G shear strength at each
C.Jm section mid point of pile
d
m
G diameter of pile at each C.J
m section mid point of pile
P
mi
G pile load at the middle of
each section

E0a)ple -!7
etermine the design bearing
capacity of a pile %#m pile
driven in to clay with
characteristic undrained shear
strength %(>Pa and %.(kPa
increase per metre depth. Piling
condition is assumed to be
favourable and the safety class
#. The pile is cut at %.Jm below
the ground level. Top diameter
of the pile is %+(mm and growth
in diameter is ,mmDm.
0igure J?' 7xample J.L
N:ften it is assumed that
cohesive strength of the soil in
the fires three meters is half the
values at the bottom.
solution:
0irst decide which part of the
pile is heavily loaded. To do so,
divide the pile which is in
contact with the soil in three
parts or sections @see fig.'.%5 in
this example the pile is divided
into three C.Jm parts
)alculate and decide diameter
of the pile at the mid point of
each C.Jm section
@(.%+(H(.((,@y
i
5 B y
i
growth per
meter from the end point.
)alculate the shear strength of
the soil at the mid point of each
C.Jm section )
mi
G @## ? %@y
i
5 5.
*hear strength at the end of the
pile G @%(-Pa H %-Pa
@%#m55G## -Pa
ecide the values of the partial
coefficients from table 82. .
2.+:
%art
y
mi#see
fig. ,.*)
m
d
mi
E #9.$79G9.998
<= > .eq_:

T#top)
section
7./, 9.&,8
2#middle)
section
,.&, 9.&&/
8#bottom)
section
$./, 9.$8.

"
ti
; pile load at t,e top of
eac, section
%art
y
ti
m
m
T#top)
,,.$ $9., 9.&/,
2#middle)
(7.& /.9 9.&*(
8#bottom)
$8., (.,
G stress at the top of the pile

The bearing capacity of the
pile is JJ.%k4
4ow using the equation in @L?&5,
we will check the pile for failure
f
9ed
G %%-Pa @see section J.L5

n
G (.,

n
G %.%
G
!n consideration of failure in the
pile material, the pile can be
loaded up to ,.( -Pa
!n consideration of cohesion
force, the pile can be loaded up
to JJ -Pa
the bearing capacity of the pile
is therefore, JJ -Pa

-!7! Si)plified )et,od of
predictin( t,e bearin(
capacit/ of ti)ber piles
)onsider the previous case and
use the following formula /


regarded the pile in its full
length
calculate average diameter of
the pile <=.eq_
calculate average shear
strength of the pile<=.eq_
C. decide the values of
9d, m
and @table 2. . 2.+5 /

9d,
G %.&

m
G %.+<=.eq_ @(.+5 G %.''
G %.#
the bearing capacity of the
pile is JL k4

Pile Foundation Design: A Student Guide
DESIG' OF
"I%E GROU"
Introduction
Group action in piled
foundation/ -ost of pile
foundations consists not of a single
pile, but of a group of piles, which
act in the double role of reinforcing
the soil, and also of carrying the
applied load down to deeper,
stronger soil strata. 0ailure of the
group may occur either by failure
of the individual piles or as failure
of the overall block of soil. The
supporting capacity of a group of
vertically loaded piles can, in many
cases, be considerably less than
the sum of the capacities the
individual piles comprising the
group. 8rope action in piled
foundation could result in failure or
excessive settlement, even though
loading tests made on a single pile
have indicated satisfactory
capacity. !n all cases the elastic
and consolidation settlements of
the group are greater than those of
single pile carrying the same
working load as that on each pile
within the group. This is because
the 1one of soil or rock which is
stressed by the entire group
extends to a much greater width
and depth than the 1one beneath
the single pile &fig"3-()
0igure L?% )omparison of stressed 1one beneath single
pile and pile group

%earnin( out co)e
When students complete this
section, they will be able/
o to calculate and
predict design
bearing capacity of
pile group in
different soil types
o to appreciate the
governing factors
in design of group
of piles
o to design pile
groups with
appropriate pile
spacing
7! *earin( capacit/ of pile
(roups
Pile groups driven into sand may
provide reinforcement to the soil.
!n some cases, the shaft capacity
of the pile driven into sand could
increase by factor of # or more.
=ut in the case of piles driven into
sensitive clays, the effective stress
increase in the surrounding soil
may be less for piles in a group
than for individual piles. this will
result in lower shaft capacities.
0igure L?# ;nder axial or lateral
load, !n a group, instead of failure
of individual piles in the group,
block failure @the group acting as a
block5 may arise.
0igure L?# =lock failure
!n general ,the bearing capacity of
pile group may be calculated in
consideration to block failure in a
similar way to that of single pile, by
means of equation '?%,but hear .s
as the block surface area and .b
as the base area of the block or by
rewriting the general equation we
get/

where"
-
s
, surface area of bloc2
-
b
E base area of bloc2 #see
fig..-()

b
,
s
E average cohesion of
clay around the group and
beneath the group.
:
c
E bearing capacity factor.
)or depths relevant for piles,
the appropriate value of :
c is
8
H
p
and H
s
E weight of pile
respective weight of soil

!n examining the behaviour
of pile groups it is necessary
to consider the following
elements/
a free?standing group, in
which the pile cap is not in
contact with the underlying
soil.
a Epiled foundation,E in
which the pile cap is in
contact with the underlying
soil.
pile spacing
independent calculations,
showing bearing capacity
of the block and bearing
capacity of individual piles
in the group should be
made.
relate the ultimate load
capacity of the block to the
sum of load capacity of
individual piles in the
group @ the ratio of block
capacity to the sum of
individual piles capacity5
the higher the better.
!n the case of where the
pile spacing in one
direction is much greater
than that in perpendicular
direction, the capacity of
the group failing as shown
in 0igure L?# b5 should be
assessed.

.1.1 Pile !roups in cohesive
soil
0or pile groups in cohesive soil,
the group bearing capacity as a
block may be calculated by mans
of e.q. '?J with appropriate 4c
value.
.1.2 Pile !roups in non-
cohesive soil
0or pile groups in non?cohesive
soil, the group bearing capacity as
a block may be calculated by
means of e.q. '?&
.1.3 Pile !roups in sand
!n the case of most pile groups
installed in sand, the estimated
capacity of the block will be well in
excess of the sum of the individual
pile capacities. .s a conservative
approach in design, the axial
capacity of a pile group in sand is
usually taken as the sum of
individual pile capacities calculated
using formulae in '?+.

Worked 7xample L?%
)alculate the bearing capacity and
group efficiency of pile foundation
installed in uniform clay of bulk unit
weight, of #(k4Dm
C
and
undrained shear strength of )u of
J(k4Dm
#
. The foundation consists
of #J piles each %+m long ,(.'m in
diameter and weight L(k4. The
weight of the pile cap is L((k4 and
founded %m below the ground
level. The adhesion factor for the
soilDpile interface has a value of
(.+

0igure L?C Worked 7xample L?%


"#$%T&#'
)alculate single pile bearing
capacity/
9s G <=.eq_ )s <=.eq_ .s
G (.+ <=.eq_ J( <=.eq_ %+
<=.eq_ <=.eq_ @(.'5 G
,('k4
?
9b G 4c <=.eq_ )b <=.eq_ .b G ,
<=.eq_ J(<=.eq_
<=.eq_ @(.#5
#
G JL.Lk4
9ci G 9si H 9bi G ,(' H JL.L G ,L(
@Wp HWcap5 ? Ws G @L(? #JH@L((?
#(? J.(? J.(? %.(55 ? @#(? %+
<=.eq_ <=.eq_ @(.#5
#
<=.eq_ #J G 'L,k4
??
total load capacity of #J piles G
9uc#J G @9ci G 9si H 9bi5 <=.eq_ #J
? O@Wp HWcap5 ? WsP G ,L(<=.eq_
#J ? 'L, G #CJC%k4
calculate block load capacity /
G ' ? @%+? '.'? J(<=.eq_ (.+5H
J(<=.eq_ '.' ? '.' <=.eq_ ,
G #JLJ(k4

?
surface area of pile group
??
weight of soil replaced by pile cap


Pile Foundation Design: A Student Guide
"ile spacin(
and pile
arran(e)ent
!n certain types of soil, specially in
sensitive clays, the capacity of
individual piles within the a closely
spaced group may be lower than
for equivalent isolated pile.
3owever, because of its
insignificant effect, this may be
ignored in design. !nstead the main
worry has been that the block
capacity of the group may be less
than the sum of the individual piles
capacities. .s a thumb rule, if
spacing is more than # ? C pile
diameter, then block failure is most
unlikely.
!t is vital importance that pile group
in friction and cohesive soil
arranged that even distribution of
load in greater area is achieved.
6arge concentration of piles under
the centre of the pile cap should be
avoided. This could lead to load
concentration resulting in local
settlement and failure in the pile
cap. 2arying length of piles in the
same pile group may have similar
effect.
0or pile load up to C((k4, the
minimum distance to the pile cap
should be %(( mm
for load higher than C((k4, this
distance should be more than %J(
mm.
!n general, the following formula
may be used in pile spacing/
5nd-bearing and friction piles" 3 E &.,
<= >? B>I>CAC >A> > .eq_.q_
+ohesion piles" 3 E (.,<= >? B>I>CAC > .eq_.q
!here:
d 7 assumed pile diameter
6 7 assumed pile length
S 7 pile centre to centre
distance .spacing/
E$ample :-(
. retaining wall imposing a
weight of %#(k4Dm including
self?weight of the pile cap is
to be constructed on pile
foundation in clay. Timber
piles of #J(mm in diameter
and each %'m long with
bearing capacity of ,(k4Dst
has been proposed. .sses
suitable pile spacing and pile
arrangement.

"olution:
%. recommended minimum
pile spacing/
* G C.J<=.eq_ @d5 H (.(#
<=.eq_ 6 G C.J <=.eq_
@(.#J5 H (.(# <=.eq_ %' G
%.%L m
?
#. try arranging the piles into two
rows/
vertical load G %#(k4D-
single pile load capacity G
,(k4Dst
G $.((m
spacing in the two rows <=.eq_
minimum distance to the edge of
the pile G (.%m <=.eq_ * G #
<=.eq_ (.% H (.#J H %.%( G
%.JJm

?
here because of the descending nature of the
pile diameter a lesser value can be taken , say
%.%(m


Pile Foundation Design: A Student Guide
"I%E
I'ST&%&TIO
' 5ETHODS
<! Introduction
The installation process and
method of installations are equally
important factors as of the design
process of pile foundations. !n this
section we will discuss the two
main types of pile installation
methodsB installation by pile
hammer and boring by mechanical
auger.
!n order to avoid damages to the
piles, during design, installation
-ethods and installation
equipment should be carefully
selected.
!f installation is to be carried out
using pile?hammer, then the
following factors should be taken in
to consideration/
the si1e and the weight of
the pile
the driving resistance
which has to be overcome
to achieve the design
penetration
the available space and
head room on the site
the availability of cranes
and
the noise restrictions
which may be in force in
the locality.

<!# "ile drivin( )et,ods
8displace)ent piles:
-ethods of pile driving can
be categorised as follows/
$. ropping weight
&. 7xplosion
(. 2ibration
*. Qacking @restricted to
micro?pilling5
,. Qetting

(.2.1 Drop hammers
. hammer with approximately the
weight of the pile is raised a
suitable height in a guide and
released to strike the pile head.
This is a simple form of hammer
used in conjunction with light
frames and test piling, where it
may be uneconomical to bring a
steam boiler or compressor on to a
site to drive very limited number of
piles.
There are two main types of drop
hammers/
*ingle?acting steam or
compressed?air hammers
ouble?acting pile
hammers
$. *ingle?acting steam or
compressed?air comprise
a massive weight in the
form of a cylinder @see
fig.+?%5. *team or
compressed air admitted
to the cylinder raises it up
the fixed piston rod. .t the
top of the stroke, or at a
lesser height which can be
controlled by the operator,
the steam is cut off and the
cylinder falls freely on the
pile helmet.
&. ouble?acting pile
hammers can be driven by
steam or compressed air.
. pilling frame is not
required with this type of
hammer which can be
attached to the top of the
pile by leg?guides, the pile
being guided by a timber
framework. When used
with a pile frame, back
guides are bolted to the
hammer to engage with
leaders, and only short
leg?guides are used to
prevent the hammer from
moving relatively to the top
of the pile. ouble?acting
hammers are used mainly
for sheet pile driving.

)igure 7-$ %ile driving using hammer
(.2.2 Diesel hammers
.lso classified as single and
double?acting, in operation, the
diesel hammer employs a ram
which is raised by explosion at the
base of a cylinder. .lternatively, in
the case of double?acting diesel
hammer, a vacuum is created in a
separate annular chamber as the
ram moves upward, and assists in
the return of the ram, almost
doubling the output of the hammer
over the single?acting type. !n
favourable ground conditions, the
diesel hammer provide an efficient
pile driving capacity, but they are
not effective for all types of ground.
(.2.3 Pile drivin! )y
vi)ratin!
2ibratory hammers are usually
electrically powered or
hydraulically powered and consists
of contra?rotating eccentric masses
within a housing attaching to the
pile head. The amplitude of the
vibration is sufficient to break down
the skin friction on the sides of the
pile. 2ibratory methods are best
suited to sandy or gravelly soil.
=ettin(/ to aid the penetration of
piles in to sand or sandy gravel,
water jetting may be employed.
3owever, the method has very
limited effect in firm to stiff clays or
any soil containing much coarse
gravel, cobbles, or boulders.

<!$ *orin( )et,ods 8 non.
displace)ent piles:
(.3.1 *ontinuous +li!ht
,u!er (*+,)
.n equipment comprises of a
mobile base carrier fitted with a
hollow?stemmed flight auger which
is rotated into the ground to
required depth of pilling. To form
the pile, concrete is placed through
the flight auger as it is withdrawn
from the ground. The auger is
fitted with protective cap on the
outlet at the base of the central
tube and is rotated into the ground
by the top mounted rotary
hydraulic motor which runs on a
carrier attached to the mast. :n
reaching the required depth, highly
workable concrete is pumped
through the hollow stem of the
auger, and under the pressure of
the concrete the protective cap is
detached. While rotating the auger
in the same direction as during the
boring stage, the spoil is expelled
vertically as the auger is withdrawn
and the pile is formed by filling with
concrete. !n this process, it is
important that rotation of the auger
and flow of concrete is matched
that collapse of sides of the hole
above concrete on lower flight of
auger is avoided. This may lead to
voids in filled with soil in concrete.
The method is especially effective
on soft ground and enables to
install a variety of bored piles of
various diameters that are able to
penetrate a multitude of soil
conditions. *till, for successful
operation of rotary auger the soil
must be reasonably free of tree
roots, cobbles, and boulders, and it
must be self?supporting.
uring operation little soil is
brought upwards by the auger that
lateral stresses is maintained in
the soil and voiding or excessive
loosening of the soil minimise.
3owever, if the rotation of the
auger and the advance of the
auger is not matched, resulting in
removal of soil during drilling?
possibly leading to collapse of the
side of the hole.
0igure +?# )0. Process
(.3.2 %nderreamin!
. special feature of auger bored
piles which is sometimes used to
enable to exploit the bearing
capacity of suitable strata by
providing an enlarged base. The
soil has to be capable of standing
open unsupported to employ this
technique. *tiff and to hard clays,
such as the 6ondon clay, are ideal.
!n its closed position, the
underreaming tool is fitted inside
the straight section of a pile shaft,
and then expanded at the bottom
of the pile to produce the
underream shown in fig. +?
C.4ormally, after installation and
before concrete is casted, a man
carrying cage is lowered and the
shaft and the underream of the pile
is inspected.
0igure + ?C a5hydraulic rotary drilling equipment b5 ).0.., c5undrreaming tool open
position
(.3.3 *.-.D.P
0igure +?', )ontinuous helical
displacement piles/ a short, hollow
tapered steel former complete with
a larger diameter helical flange,
the bullet head is fixed to a hallow
drill pipe which is connected to a
high torque rotary head running up
and down the mast of a special rig.
. hollow cylindrical steel shaft
sealed at the lower end by a one?
way valve and fitted with triangular
steel fins is pressed into the
ground by a hydraulic ram. There
are no vibrations.
isplaced soil is compacted in
front and around the shaft. :nce it
reaches the a suitably resistant
stratum the shaft is rotated. The
triangular fins either side of its
leading edge carve out a conical
base cavity. .t the same time
concrete is pumped down the
centre of the shat and through the
one?way valve. 9otation of the fins
is calculated so that as soil is
pushed away from the pile base it
is simultaneously replaced by in?
flowing concrete. 9ates of push,
rotation and concrete injection are
all controlled by an onboard
computer. Torque on the shaft is
also measured by the computer.
When torque levels reach a
constant low value the base in
formed. The inventors claim that
the system can install aR typical
pile in %# minute. . typical Lm long
pile with an +((mm diameter base
and CJ(mm shaft founded on
moderately dense gravel beneath
soft overlaying soils can achieve
an ultimate capacity of over #((t.
The pile is suitable for
embankments, hard standing
supports and floor slabs, where
you have a soft silty layer over a
gravel strata.
0igure + ?' ).3..P.

Back to Top

Pile Foundation Design: A Student Guide
%O&D TEST
O' "I%ES
>! Introduction
Pile load test are usually carried
out that one or some of the
following reasons are fulfilled/
To obtain back?figured soil
data that will enable other
piles to be designed.
To confirm pile lengths and
hence contract costs
before the client is
committed to over all job
costs.
To counter?check results
from geotechnical and pile
driving formulae
To determine the load?
settlement behaviour of a
pile, especially in the
region of the anticipated
working load that the data
can be used in prediction
of group settlement.
To verify structural
soundness of the pile.
Test loadin(/ There are four
types of test loading/
compression test
uplift test
lateral?load test
torsion?load test
the most common types of test
loading procedures are )onstant
rate of penetration @)9P5 test and
the maintained load test @-6T5.

..1.1 */P (constant rate of
penetration)
!n the )9P @constant rate of
penetration5 method, test pile is
jacked into the soil, the load being
adjusted to give constant rate of
downward movement to the pile.
This is maintained until point of
failure is reached.
0ailure of the pile is defined in to
two ways that as the load at which
the pile continues to move
downward without further increase
in load, or according to the =*, the
load !hich the penetration reaches a
value e?ual to one1tenth of the
diameter of the pile at the base.
0ig.,?#, !n the cases of where
compression tests are being
carried out, the following methods
are usually employed to apply the
load or downward force on the pile/
. platform is constructed on the
head of the pile on which a mass
of heavy material, termed
EkentledgeE is placed. :r a bridge,
carried on temporary supports, is
constructed over the test pile and
loaded with kentledge. The ram of
a hydraulic jack, placed on the pile
head, bears on a cross?head
beneath the bridge beams, so that
a total reaction equal to the weight
of the bridge and its load may be
obtained.
..1.2 0$T1 the maintained
increment load test
0ig.,?%, the maintained increment
load test, kentledge or adjacent
tension piles or soil anchors are
used to provide a reaction for the
test load applied by jacking@s5
placed over the pile being tested.
The load is increased in definite
steps, and is sustained at each
level of loading until all settlements
has either stop or does not exceed
a specified amount of in a certain
given period of time.
0igure ,?% test load arrangement using kentledge

0igure ,?# test being carried out


Pile Foundation Design: A Student Guide
%i)it State
Desi(n
Introduction
Traditionally, design
resistance of foundations
has been evaluated on an
allowable stress basis that
piles were designed with
ultimate axial capacity
between # and C times than
working load. 3owever
structural design is now
using a limit state design
@6*5 bases whereby partial
factors are applied to various
elements of the design
according to the reliability
with which the parameters
are known or can be
calculated. 6* approach is
the base of all the
7urocodes, including that for
foundations design. !t is
believed that 6imit state
design has many benefits for
the economic design of
piling. The eurocode
approach is particularly
rigorous, and this guide
adopts the partial factors
presented in the codes.
Elements of Soil Mechanics (8th Edition) to learn how to design
piles (and other geotechnical structures) to Eurocode 7.
Eurocode ? divides
investigation, design and
implementation of
geoconstructions into three
categories. !t is a
requirement of the code that
project must be supervised
at all stages by personnel
with geotechnical
knowledge.
!n order to establish
minimum requirements for
the extent and quality of
geotechnical investigation,
deign and construction three
geotechnical categories
defined. These are/
8eotechnical )ategory %, #,
C.
2! Goetec,nical cate(or/
3 GC
this category includes small
and relative simple
structures/
?for which is impossible to
ensure that the fundamental
requirements will be satisfied
on the basis of experience
and qualitative geotecnical
investigationB
?with negligible risk for
property and life.
8eotechnical )ategory %
procedures will be only be
sufficient in ground
conditions which are known
from comparable experience
to be sufficiently straight?
forward that routine methods
may be used for foundation
design and construction.
Fualitative geotechnical
investigations
2!# Geotec,nical
Cate(or/3 GC #
This category includes
conventional types of
structures and foundations
with no abnormal risks or
unusual or exceptionally
difficult ground or loading
conditions. *tructures in
8eotechnical category #
require quantitative
geotechnical data and
analysis to ensure that the
fundamental requirements
will be satisfied, but routine
procedures for field and
laboratory testing and for
design and execution may
be used. Fualified engineer
with relevant experience
must be involved.
2!$ Geotec,nical
Cate(or/3 GC $
This category includes
structures or parts of
structures which do not fall
within the limits of
8eotechnical )ategories
%and #.
The following are examples
of structures or parts of
structures complying with
geotechnical category #/
conventional type of /
spread foundationsB
raft foundationsB
piled foundationsB
walls and other
structures retaining for
supporting soil or
waterB
excavationsB
bridge piers and
abutmentsB
embankment and
earthworksB
ground anchors and
other tie?back
systemsB
tunnels in hard, non?
fractured rock and not
subjected to special
water tightness or
other requirement.
Geotec,nical Cate(or/ $
includes very large or
unusual structure. *tructures
involving abnormal risks or
unusual or exceptionally
difficult ground or loading
conditions and highly seismic
areas. Fualified geotechnical
engineer must be involved.
The following factors must
be considered in arriving at a
classification of a structure or
part of a structure/
4ature and si1e of the
structure
6ocal conditions, e.g.
traffic, utilities,
hydrology,
subsidence, etc.
8round and
groundwater
conditions
9egional
seismicityS..
12.3.1 *onditions
classified as in 3urocode 4
!n the code, conditions are
classified as favourable or
unfavourable.
Favourable conditions are
as suc,:
@ if experience shows that
the material posses limited
spreading characteristic
@ if large scale investigation
was carried out and test
results are reliable
@ the existence of well
documented investigation
carried out using reliable
methods which can give
reproducible results
@ if additional tests,
investigations and
supervisions are recommend
@ high certainty in defining
test results
@ failure is plastic

Unfavourable conditions
are as suc,:
.. if experience shows that
the material posses
spreading characteres
.. if test results shows large
spreading than the normal
conditions
.. if the extent of
investigation is limited
.. limited experience and
methods lucking
reproducibility
.. where there is no
recommendation for
additional test, investigations
and supervision
.. uncertainty in analysing
test results
.. if failure is brittle
7urocode & refers to
foundation loadings as
action. The se can be
permanent as !n the case of
weights of structures and
installations, or variable as
imposed loading, or wind
and snow loads. They can be
accidental, e.g. vehicle
impact or explosions.
.ctions can vary spatially,
e.g. self?weights are fixed
@fixed actions5, but imposed
loads can vary in position
@free actions5. The duration
of actions affections affects
the response of the ground.
!t may cause strengthening
such as the gain in strength
of a clay by long?term
loading, or weakening as in
the case of excavation
slopes in clay over the
medium or long term. To
allow for this 7urocode &
introduces a classification
related to the soil response
and refers to transient
actions @e.g. wind loads5,
short?term actions @e.g.
construction loading5 and
long?term actions. !n order to
allow for uncertainties in the
calculation of he magnitude
of actions or combinations of
actions and their duration
and spatial distribution,
7uorcode requires the
design values of actions +
d
to
be used for the geotechnical
design either to be assessed
directly or to be derived from
characteristic values +
k
/
+
d
= +
k
2!+ T,e partial factors
)3
n3 Rd
T,e partial factor
)
: this
factor is applied as a safety
factor that the characteristic
values of the material is
divided by this factor. @m G
material index5 and covers /
unfavourable
deviation from the
material product
property
inaccuracies in the
conversion factors/
and
uncertainties in the
geometric properties
and the resistance
model.
!n ultimate limit state,
depending upon a given
conditions, for 8eotechnical
)ategory #, the values of the

m
may be decided using
table %(?%T %(?#.
T,e partial co.efficient
n
/
in order to ensure stability
and adequate strength in the
structure and in the ground,
in the code, cases ., =, and
) have been introduced.
2alues of
n
is given in table
%(?C
"artial co.efficient
Rd
/ this
co?efficient is applied in
consideration of deviation
between test results and
future construction. 2alues of
the
n
should be between
%.' ? %.+
Table 2. partial factors on )aterial
properties for conventional desi(n
situations for ulti)ate li)it states
-aterial property
tan
modules
other properties

Table 2.# partial factors on )aterial
properties for conventional desi(n
situations for service li)it state
-aterial property
modules
other properties
'or)all/ t,e desi(n values3 d 3 Ed3 tan 3
can be decided usin( t,e follo9in(
for)ulae:
f
d
7 f
8
A.
n <= B B .eq_oo
C
E
d
7 E
8
A.
n <= B B .eq_oo
C
tan
d
7 tan
8
A.
n <= B B .eq_oo
C
9here:
f 7 reaction force
7 internal angle of friction
E 7 elastic module
Table 2.$ partial factor n
)lass
n
. %.(
= %.%
) %.#

Table 2.+ ad,esion factor
pile
)oncrete piles (.J
*teel piles (.J
timber piles @wood piles5 (.J

The table is used for qc ? %( -pa
Table 2.- *earin( factors ' 3 'A3 'C
d 4 4) 4q
#J L.'+ #(.& %(.&
#L &.L' ##.# %%.+
#& +.,, #C., %C.#
#+ %(.L #J.+ %'.&
#, %#.J #&., %L.'
C( %'.& C(.% %+.'
C% %&.' C#.& #(.L
C# #(.L CJ.J #C.#
CC #'.' C+., #L.%
C' #,.( '#.# #,.'
CJ C'.' 'L.% CC.C
CL '%., J(.L C&.&
C& ',.% JJ.L '#.,
C+ J+., L%.C '+.,
C, &(., L&., JL.(
'( +J.L &J.C L'.#
'% %(' +C., &C.,
'# %#L ,C.& +J.'
'C %J' %(J ,,.(
'' %,( %%+ %%J
'J #C' %C' %CJ