guideline for piling works -...

GUIDELINE FOR PILING

WORKS

Disediakan Oleh: Unit Geoteknik Cawangan Pakar & Kejuruteraan Awam Ibu Pejabat Jkr Malaysia Tkt 10, Menara Tun Ismail Mohamaed Ali No. 25, Jalan Raja Laut,

50350 Kuala Lumpur

Unit Kej. Geoteknik, CPKA, JKR Malaysia

11.7.2017

1

GUIDE LINE FOR PILING

BIL CONTENTS PAGES

1.0 INTRODUCTION 2 - 3

2.0 PILE DESIGN CRITERIA 3 - 4

3.0 CLASSIFICATION OF PILES 4 - 7

4.0 PILE SELECTION CRITERIA 8

5.0 COMMON TYPES OF PILES 8 - 9

5.1 BAKAU PILES 10 - 11

5.2 TREATED TIMBER PILES 12 - 13

5.3 PRECAST R.C. PILES 13 - 16

5.4 PRESTRESSED CONCRETE PILES 16 - 17

5.5 BORED PILES 17 - 21

5.6 STEEL PILES 21 - 22

5.7 MICRO PILES 22 - 24

6.0 BEARING CAPACITY OF PILES 25 - 26

6.1 UNIT SHAFT RESISTANCE fs 26

6.2 UNIT POINT RESISTANCE q 27

6.3 ESTIMATION OF NEGATIVE SKIN FRICTION 27 - 28

6.4 SETTLEMENT OF SINGLE PILES 28 - 29

6.5 LATERAL CAPACITY OF PILES 29

6.6 PILE GROUP ANALYSIS 29 - 30

7.0 LOAD TEST 30 - 33

8.0 THE HILEY FORMULA 34 - 39

Introduction.doc

Introduction.doc

Pile%20Design%20Criteria.doc

Pile%20Design%20Criteria.doc

Classification%20of%20Piles.doc

Pile%20Selection%20Criteria.doc

Bakau%20Piles.doc

Treated%20Timber%20Piles.doc

Precast%20R.C.%20Piles.doc

Prestressed%20Concrete%20Piles.doc

Bored%20Piles.doc

Steel%20Piles.doc

Micropiles.doc

Bearing%20Capacity%20of%20Piles.doc



Estimation%20of%20Negative%20Skin%20Friction.doc

Pile%20Capacity.doc

Pile%20Capacity.doc

Pile%20Capacity.doc

Load%20Test.doc

Heiley%20Formula.doc


11.7.2017

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1. 0 INTRODUCTION.

Generally piles foundations are used to support structures when suitable

founding levels are deeper than 3m below the formation levels or when

shallow foundation are not suitable due to stability problems or inadequate

bearing capacity at shallow depth or other peculiar site conditions.

Any rational approach to estimate the safe load capacity of a pile requires

understanding and grasping of the following spectrum of subjects/aspects.

a. Classification and types of piles available, their general characteristics,

basic technical specifications and the typical installation controls.

b. Factors governing the choice of pile type (site and subsoil conditions,

environment, geology, durability, loading, cost, possibility of

imperfections in piles and their consequences).

c. Geotechnical capacity requirements

- site investigation

- capacity and settlement of pile in cohesive/cohesionless soils by

dynamic and static formulae

- group effect

- negative skin friction

d. Structural requirements

- handling stress

- driving stress

- working stress

- structural capacity

- discount for structural capacity due to joint, slenderness, and

drivability/uncertainty.

e. Quality controls:

- materials

- workmanship/tolerances

- pile testing for load capacity, settlement and integrity

- construction control measure


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f. Sensitivity of pile performance prediction (capacity and settlement)

- method of analysis used

- generalization of sub soil profile

- selection of design parameters

- method of installation

2. 0 PILE DESIGN CRITERIA

Fundamentally the pile foundation design is considered safe and sound if the

soil/rock and pile material are not over-stressed during the installation and

service life. (Permissible stress method is used in BS 8004; NOT limit state

method).

The general pile design criteria and considerations are as follows:

a. The pile material itself must not be structurally over-stressed during handling,

installation and working conditions. This criterion requires compliance based

on code of practice and experiences.

b. There must be an adequate factor of safety (FOS) against ultimate failure.

FOS for geotechnical capacity should be at least 2, based on lower bound

shear strength obtained from adequate site investigation. This criterion is to

cater for statistical uncertainty or risk factor.

c. BS 8004 Clause 2.1.2 defines that foundation design should ensure that

foundation movement (vertical & horizontal) are within limits that can

tolerated by the proposed structure without impairing its function. Angular

distortion generally shall not exceed 1:150 for framed R.C structures. This

criterion is to ensure the superstructure is not over-distorted. Piles settle less

than 12mm at design load (2 x working load) are generally satisfactory for

R.C. framed structures. Under lateral and bending movement perpendicular to

the axis of pile, the permissible lateral movement is usually 12mm for most

R.C. framed structures.


11.7.2017

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d. Control of the installation effects of the structures and its necessary

construction operations to limits noise level and displacement or movement of

ground at and under nearby piles, buildings, roads and utilities to tolerable

amount both during and after the work shall be specified. This criterion is

commonly and conveniently overlooked when detail information is not

available.

e. Durability aspects and quality control with respect to materials, workmanship

& loading test etc. must comply with BS 8004 and JKR standard specification

for Piles in Building Projects (1991). For precast concrete piles, MS 1314

(1993) shall be complied in respect of quality control in production and

minimum structural requirements.

f. Other important design criteria that should be considered are

- possible scour and its effect on pile capacity

- pile group effect

- negative friction or pile in settling ground

3. 0 CLASSIFICATION OF PILE

Classification of pile is a useful tool to estimate or generalize the potential

behavior and characteristics of the pile under variety of conditions. According

to BS 8004, piles can be broadly classified as displacement and non-

displacement piles. Details of the classification are shown in Fig.1.

3.1 PILE CLASSIFICATION ACCORDING TO INSTALLATION

a) Displacement piles

Driven preformed timber, concrete or steel piles have ground vibration and

possible ground heave problems. Installation of displacement pile is fast

and cheap.

- Driven solid pile (concrete or closed end pipes)

- Driven small displacement piles (H piles or open end pipes)


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- Driven & cast in-place

- Jacked piles (steel or concrete)

Important installation issues are:

- Installation sequences:- inner piles in a group should be driven first

- Pile position deviation tolerance:- < 75mm

- Verticality tolerance:- 1 in 75

- Cut off pile position deviation:- < 75mm

- Type & capacity of hammer & helmet:- depend on environmental

factors & driveability

- Pile heave problem:- checking & redriving where necessary.

- Predrilling requirement:- avoid overdriving through very hard stratum.

- Pile rejection before & after installation:- Material quality

workmanship, position tolerance limits, capacity & integrity (static &

dynamic tests etc).

b) Non-displacement piles:

Environmentally more friendly

- Bored piles

- Micropiles

- Hand dug caissons

- Continuous flight augured piles

3.2 PILES CLASSIFICATION ACCORDING TO BEARING.

- End bearing piles

- Frictional piles

- Partly end bearing & partly frictional piles

3.3 PILES CLASSIFICATION ACCORDING TO MATERIALS

- Concrete piles (RC or prestressed, square or cylindrical.)

- Timber piles (bakau or treated timber)

- Steel piles (H or pipe)

- Composite piles


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3.4 PILE CLASSIFICATION ACCORDING TO FUNCTIONS

- Compression piles

- Tension piles

- Batter/rake piles

3.5 PILE CLASSIFICATION ACCORDING TO SHAPES

- Square

- Circular

- Triangular

- H section

- Hexagonal or octagonal


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TYPE OF PILES

DISPLACEMENT PILES NON-DISPLACEMENT PILES

Bored piles (450mm – 1500mm Ø)

= 60T – 100T

Micro piles (150mm – 300mm Ø)

= 10T – 120T

Flight auger pile (300mm – 500mm Ø)

= 30T – 100T

TOTAL PREFORMED

PILES

(A ready-made pile is driven

into the ground)

DRIVEN CAST

IN-PLACE PILES

(A tube is driven

into the ground to

form void)

Hollow

(Small displacement)

Solid

Concrete Tube Steel Tube

Closed ended tube concreted

with tube left in position

(60T – 200T)

Open ended tube

extracted while

cocreting (Franki)

(67T – 150T)

Closed ended tube

(80T – 300T)

Steel Pipe

(250mm – 900mm Ø)

55T – 430T

Concrete Spun Pile

(300mm – 800mm Ø)

50T – 350T

Bakau pile

(75mm – 150mm Ø )

0.5T – 1T

Treated timber pile

(125mm – 150mm Ø)

10T – 15T

Steel H-pile

(Small displement)

200mm x 200mm -

350mm x 350mm

43T – 308T (G43A)

60T – 308T (G50B)

Concrete

Precast R.C. Pile

200mm x 200mm to

400mm x 400mm

25T – 145T

Precast Prestressed Pile

200mm x 200mm to

400mm x 400mm

35T – 160T

Notes:

1. Ranges of capacity

indicated are based on

pile sizes commonly

used in JKR

2. 1 T = 10 KN

FIG.1 – CLASSIFICATION OF PILES


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4. 0 PILE SELECTION CRITERIA ( DESIGN CONSIDERATIONS)

Suitable uses of various common types pf pile under various design

considerations are shown in Fig.2. The choice or a particular pile type for a

particular project can be a complex decision even experts in the field, and of

course, in some cases, there is no unique solution. The important consideration

are geotechnical factors and it should be remembered that even with proper

site investigation, the possibility of variation in pile length or pile types during

construction is something not uncommon. This is because there will always be

some risk of unknown conditions and it can only be minimized by a more

thorough investigation and studies. The degree of success reflects the skill and

imagination of those involved, but it also depends on circumstances beyond

their control (Sowers, 1997).

In built up or urban areas or locations adjacent to sensitive structures, non

displacement piles (or jacked in piles) should be used as they are

environmentally more friendly in respect of noise and vibration levels.

Generally for driven piles, hydraulic hammer or drop hammer is preferred to

diesel hammers which are more environmental unfriendly in respect of more

noise and smoke pollutions.

5.0 COMMON TYPES OF PILES

A pile designer shall grasp sufficient fundamental knowledge about various

types of piles available and their general characteristics so that the suitability

of a pile type for a specific project at a specific site can be assessed. General

characteristics of pile design and construction of common types of piles used

by JKR are discussed in the following paragraphs.

Unit Kej. Geoteknik, CPKA, JKR Malaysia 11.7.2017

9

TYPE OF PILES

DESIGN CONSIDERATION

PREFORMED

BO

RE

D P

ILE

S

MIC

RO

PIL

ES

BA

KA

U P

ILE

S

TIM

BE

R P

ILE

S

PR

EC

AS

T R

.C. P

ILE

S

PR

ES

TR

ES

S C

ON

C.

PIL

ES

SP

UN

PIL

ES

ST

EE

L H

-PIL

ES

ST

EE

L P

IPE

P

ILE

S

SC

AL

E O

F L

OA

D

(ST

RU

CT

UR

AL

)

COMPRESSIVE LOAD PER COLUMN

<100 KN ? ? ? ? ? X ?

100 - 300 ? ? X

300 - 600 ?

600 - 1100 X ?

1100 - 2000 X ?

2000 - 5000 X X ?

5000 - 10000 X X ?

>10000 X X ? ?

GE

OT

EC

HN

ICA

L

BE

AR

ING

TY

PE

S

MAINLY END – BEARING

(D = Anticipated Depth Of Bearing)

D 5 m ? ? ? ? ? ? ? ?

5 – 12 m

12 – 24 m X X

24 – 34 m X X ?

34 – 60 m X X ? ? ? ? X

MAINLY FRICTIONAL ? ?

PARTLY FRICTION + PARTLY END BEARING ?

TY

PE

OF

BE

AR

ING

LA

YE

R

LIMESTONE FORMATION X ? ? ? ? ? ?

WEATHERED ROCK / SOFT ROCK X X

ROCK (RQD > 70%) X X ? ? ?

DENSE / VERY DENSE SAND X ? ?

TY

PE

OF

IN

TE

RM

ED

IAT

E L

AY

ER

COHESIVE SOIL

SOFT SPT < 4

M. STIFF SPT = 4 - 15

Y. STIFF SPT = 15 - 32 ?

HARD SPT > 32 X ?

COHESIONLESS SOIL

LOOSE SPT < 10

M. DENSE SPT = 10 - 30 ?

DENSE SPT = 38 - 50 X ?

Y. DENSE SPT > 50 X X

SOIL WITH SOME BOULDERS / COBBLES

(S = SIZE)

S < 100 mm X ?

100 – 1000 mm X X ? ? ?

1000 – 3000 mm X X ? ? ? ? ? ?

> 3000 mm X X ? ? ? ? ? ?

GROUND WATER

ABOVE PILE CAP

BELOW PILE CAP X

ENVIRONMENT

NOISE + VIBRATION = COUNTER MEASURES REQUIRED ? ? ? ? ?

PREVENTION OF EFFECTS ON ADJOINING STRUCTURES ? ? ? ? ? ? ? ?

UNIT COST

NOTE:-

INDICATES THAT THE PILE TYPE IS SUITABLE

X INDICATES THAT THE PILE TYPE IS NOT SUITABLE

? INDICATES THAT THE USE OF THE PILE TYPE IS DOUBFUL UNLESS ADDITIONAL MEASURES TAKEN


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FIG. 2 = PILE SELECTION CHART


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5.1 BAKAU PILE

- Usual sizes : 75 mm to 125 mm diameter

- Allowable load : 5 kN to 10 kN per pile

- Usual length : 6 m to 12 m with one joint

- Possible damages by insects, marine borers or fungi or dry rot.

- Usually designed as a frictional pile submerged under water table. Suitable for

low column loads, (single or double storey buildings).

- Use of bakau piles are not allowed in JKR projects since 1993

The common types of bakau timber used in piled foundation are Bakau Minyak

(Rhizophora conjugata) and Bakau Kurap (Rhizophora mucrorata). These piles,

due to the small load allowed to be carried by each pile, are used in groups and

with a relatively high factor of safety. Material defects such as straightness, size,

crack, etc. are normally not so stringently controlled. However, if extension length

is required, the joints must be properly fabricated under close supervision. The

standard JKR joint is a metal pipe collar equal in diameter to the bakau pile used.

But it is definitely difficult to find the ends of every piece of naturally-occuring

bakau timber fitting properly into the collar, especially the smaller end which is

usually smaller than the collar. Wedging pieces are necessary to ensure a stiff joint.

The durability of bakau piles is almost solely dependent on the condition that the

piles are wet all the time. The test specimens of untreated bakau piles driven to a

depth completely submerged underwater are found to be intact after 5 years and

specimens in dry ground are destroyed by termites and fungus after 3 years.

The first condition to ensure durability is that piles must be kept moist during

storage. Piles left unprotected and became dried up under sun must be rejected.

Secondly piles must be below groundwater level all the time after installation.

Groundwater level varies seasonally and during the service life of a pile. The

recommended practice is thus to take whatever stable groundwater level and have

the cut-off of piles 1 or 2 feet below the groundwater level as precaution.


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Bakau Piles are generally designed as friction piles thus any method of estimating

the safe load by impact formula formula should consider the resistance per foot run

of pile and not the resistance at the point.

It is difficult to describe a stratum or to give bearing values for different soils, but

if the resistance to penetration of a stratum is known it can be given a frictional

value. By recording the number of blows taken to drive a pile through 1 foot and

knowing the weight and fall of hammer, the resistance to penetration can be

calculated.

Mr. John Gaskin, A.M. Inst. M & Cy. E. suggests an empirical formula for arriving

at the side frictional value of a reinforced concrete pile. This formula has been

checked with numerous pile driving records and gives results agreeing

approximately with actual test loads.

The formula takes this form,

F = (Average frictional value in tonnes) per sq.ft.

__

= WH N

100A

Where,

N = average number of blows per foot

W = weight of hammer in tones

H = drop of hammer in feet

A = cross sectional area of the pile in sq.ft.

The lengths of bakau piles commonly used are 7, 12, 15 and 20 feet and using these

lengths there will probably be, at most, 3 different strata encountered; then by taking

the average number of blows per foot for each stratum, F can be calculated and by

integration the total side frictional value of the pile can be arrived at.

Alternatively if the strata are known through test pits or bores the safe load on bakau

piles can be estimated by using the values of F given below:-


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From Arrols Handbook;

Type of Soil Value of F in

tonnes per sq.ft.

Very soft silt 0.07

Still mud 0.09

Wet clay 0.10

Dry clay 0.20

Compact hard clay 0.2

Sand, gravel & sand 0.25

5.2 TREATED TIMBER PILES

- Usual sizes : 125 mm SQ, 100 kN/Pile

: 150 mm SQ, 150 kN/Pile

- Maximum length : 12m with one joint for buildings less then 2 storeys

(sleeve joint)

- Timber piles are light, easy to handle and comparatively cheap. All approved

timber pile should have SIRIM control labels. Usually designed as a frictional

or partly frictional and partly end bearing piles. Cannot stand hard driving (SPT

> 30) and driving shall be stopped for about 4 blows/25mm (1 ton hammer

with 1 to 2 ft. drop).

- Piles should be tapped gently (less ½ ft drop) before stopping driving to ensure

intact at pile joint. Tolerances of timber piles dimensions and joints are

commonly overlooked at site resulting in significant loss of friction resistance.

Use of treated timber piles in JKR projects is stipulated in KPKR circular

3/1975.

The common types timber piles used in this country are bakau piles and pressure-

treated piles usually Kempas. Treated timber piles are in 125mm 0r 150mm square

sections with standard length of 6.0m.


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Material defects in treated timber piles must be stringently checked because the

piles are allowed to carry higher loads and be used singly. The most common

defect is that piles are curved more than the 25mm limit for a 6.0m length. The real

reduction in carrying capacity of a pile curved more severely than designed is not

conclusively known.. Nevertheless if used at all, curved members must be used in

positions of lesser load. A more harmful defect is that a pile may contain sloping

grain pattern and a part of it may split off easily. Parts may split off during

transportation, when piles are unloaded by being thrown down from lorries. Piles

with sloping grains steeper than the allowable 1 in 16 limits can only be used when

strengthened with proper metal straps.

Pressure-treated timber piles are normally considered as inferior to concrete or

steel piles in terms of durability. Hence in JKR projects this form of pile is limited

to minor buildings of not more than 2 storeys and only a single joint for each pile is

allowed. This will ensure that the piles do not become too slender.

5.3 PRECAST R.C. PILES

a) Most extensively used pile type and about 87 % used in JKR building

b) R.C piles are usually cast to square section of 200 mm, 250 mm, 300 mm,

350 mm and 400 mm JKR standard with maximum length 12 m (30 tonne -

120 tonne)

c) Should design to comply with all requirements of MS 1314 (1993) JKR

specification (ILP 1/91). Class 1 R.C pile (Grade 40 concrete and min.

1.2% longitudinal reinforcement) should be used where driving stress is

difficult to control such as driving through hard strata; highly variable

subsoil, subsoil with boulders or rocks. The pile shall be designed as a

structure to resist all pitching, handling and working loads according to BS

8110 at varies concrete age. In computing the stress due to handling, the

computed load shall be increased by 50 % to account for impact and shock.

d) Max. allowable structure capacity is;


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La = ¼ fcu. A or Mc /0.15b

Max. allowable compressive stress is ¼ fcu. or 10 N/mm²

La should be discounted for joints (5n %) and slenderness, (L/b-80 )%

where; n = no of joints,

L = length of pile,

b = size of pile,

fcu = grade of concrete.

Mc = cracking moment (MS 1314)

e) Overdriving could be avoided if control driving and proper hammer are

adopted. The min. weight of the hammer, the applied energy during driving

and protective cushion shall be such that to avoid tension cracks due to

rebound while driving. Driving should be stopped if penetration is less 25

mm per 10 blows for friction piles and 12 mm per 10 blows for end bearing

piles. Maximum number of hammer blows should not exceed 1000 for

total length and 500 for the final 10 m. Generally the compressive strength

of the piles can be reduced by up to 15% to 30% after 1000 blows (Broms).

f) In dense saturated fine grained soils such as silts or fine sands, negative

pore pressure can be set up temporarily and the driving resistance may fall

as these pressures return to normal. In clays, the results are on reverse. The

necessary time interval before REDRIVING may vary from 1 hr. to 2 hr.

for non cohesive soils to 2 days or more for cohesive soils. The resistance

at the start of redriving is more likely to be true bearing value of the pile.

Piles especially and bearing piles driven in clay should be checked for

potential pile heave problem.

g) R.C. piles are generally very suitable in residual soils. R.C. piles are not

preferred to be used in the following situation:-

i) Long piles in very soft ground where the tensile stress during

driving can exceed 5 N/mm² (unless control driving, use inspection

tube to check straightness, and use grade 50 concrete; longer

centering bar and secured with grout or epoxy resin etc.). In fact,

when long piles in soft formation are required, consideration should


16

be given to the use of pre-tensioned spun piles which are better able

to resist tensile stress without cracking (due to the pre-stress and

higher hammer/pile weight ratio).

ii) Long slender piles encountering boulders, inclined or irregular

bedrock may suffer damages (unless control driving, use inspection

tube to check straightness, use grade 50 concrete and heavily

reinforced say 2 % longitudinal reinforcement to improve torsional

and bending resistance).

h) Advantages and disadvantages of precast driven R.C piles are as follows:

The Advantages:

i) Can be driven to predetermined set/depth if sub soil profile is

reasonably uniform .

ii) Stable in squeezing ground, for example soil clays, silts and peats.

iii) Pile material can be inspected before piling

iv) Can be redriven if affected by ground heave.

v) Can be driven in long lengths.

vi) Can be carried above ground level, for example, through water for

marine structures.

The Disadvantages:

i) High local stress or cracks may develop at corners & surface

especially if proper chamfers are not provided or positions &

straightness of reinforcement (cover) exceed tolerance limits ±

6mm; torsional and bending forces may be high. Have different

strength and stiffness about various axes. Liable to cracking when

weight of hammer is less than the pile weight especially in weak

soil.

ii) Heave and disturbance of surrounding soil may cause difficulties,

and damages to nearby structures and utilities pipes or cables.

iii) Cannot readily be varied in length resulting in high wastage when

used in erratic profile of hard strata formation

iv) May be damaged due to hard driving; cannot be checked unless

inspection tube is provided or PDA test are carried out.


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v) Reinforcement may be controlled by handling and driving

requirement rather than by working caused by structural loads.

vi) Cannot be driven with very large sizes or in conditions of limited

headroom.

vii) Noise, vibration and ground displacements may cause difficulties,

unless installed by pre-boring or jacking.

5.4 PRESTRESSED CONCRETE PILES

Generally, comments for pre-cast R.C. piles also are applicable to square pre-

stressed concrete pile; but pre-stressed spun piles generally have several

advantages over pre-cast R.C. piles; spun piles have uniform strength in all

directions; piles generally have higher and uniform concrete strength; straightness

of piles can be checked after installation and can stand higher tensile stress. Tensile

and torsional stress due to driving can be better resisted and less likely to produce

cracks. As pre-stressed piles generally require high concrete strength of at least

grade 50N/mm² and careful control during manufacturing, the casting yard should

be under proper shelter so as to ensure proper curing and protection.

Appendix B shows the basic structural Strengths (allowable load, bending strength

etc.) of various sizes of R.C. piles & spun piles (JKR Standard Designs)


18

APPENDIX B

STRUCTURAL STRENGTHS OF PRECAST CONCRETE PILES

(MS 1314 Part 1)

Pile Type Pile Size

(mm x mm)

Crack

Moment

(kN.m)

Ultimate

Moment

(kN.m)

Max.

Load

(kN)

Remarks

R.C. Piles

Class 1

200 x 200 5.7 15 350 Grade 40 concrete

1.2% (min) main

reinforcement

Crack moment Mc at

0.20mm crack width

Ultimate moment at zero

axial load

250 x 250 12.6 27 600

300 x 300 22.0 56 800

350 x 350 35.0 76 1150

400 x 400 50.0 111 1450

Spun Piles

Class A

250mm 17 30 450 Grade 55 concrete

Min. effective stress

5N/mm2

Average loss in pre-

stress 14%

Crack moment Mc at

0.05mm crack width

300 25 47 600

350 35 66 850

400 55 101 1100

450 80 114 1300

500 110 158 1600

600 180 265 2100

700 270 442 2800

800 400 606 3500

900 600 870 4300

1000 800 1150 5200

5.5 BORED PILES

a) Bored piles refer to Bored cast-in-place piles as specified in BS 8004.

Bored piles are formed by boring using suitable type/capacity of machines

and subsequently filling the hole with high workability concrete and some

reinforcement.

b) Usual size: 400 mm to 1.5 m diameter (60 tonne to 1000 tonne Capacity).

Piles of 600 mm or more in diameter or commonly known as large diameter

bored piles.


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c) Suitable & cost effective in typical stiff residual soil especially when

column loads are high and water table is low; noise and vibration can be

reduced to minimum and bored lengths can be varied easily, High

mobilization cost due to requirement of large & expensive plants.

d) Bored pile capacity = ¼ fcu * Ac

Where Ac = concrete section; and fcu = 20-30N/mm²,

For long piles or bored shaft consisting of sandy and water bearing strata,

lower fcu (max. 25/mm²) should be considered in the estimation of pile

capacity though higher fcu shall be specified. Settlement may be critical to

control allowable load for large diameter bored piles because settlement

may reach 0.3 – 1 % of pile size when shaft friction is fully mobilized.

e) To fully mobilize the end bearing, settlement may reach 10%-20% of pile

size depending on type/conditions of founding stratum, method of

construction & control to clean the pile base/toe.

f) Reinforcement shall be 0.5% to 1.0% for at least the top 6.0 m (minimum).

For bored piles installed in soft or loose strata, longer reinforcement up to

the base is required.

g) Temporary or sometimes permanent casing is needed for sandy water

bearing strata or very soft top strata. Bentonite suspension or polymer can

be used to stabilized bored shaft.

h) Bored piles in limestone areas need special design: overhung rock, pinnacle

or cavities need micro piles at pile base; may need permanent casing to

prevent necking. Capacity shall be downgraded by 15% - 35% to account

for several inherent uncertainty and risk.

i) For bored piles designed as end bearing piles socketed in rock, minimum

socket length to ensure high/full structural capacity shall be 1.0m or 1 pile

size into the rock with RQD exceeding 25% i.e. socket length > (1 m +


20

thickness of highly weathered rock of RQD < 25%). Minimum socket

length shall be more if the subsoil has boulders (granite formation).

j) For dry bored holes, the specified grade of concrete for quality control

purpose should be 20 – 30 N/mm² & min. cement content shall be

300kg/m³.

k) For wet holes, the specified grade of concrete should be 25 – 30 N/mm² &

min. cement content shall be 400kg/m³.

l) The fcu considered for designing the maximum structural capacity should

not exceed 25N/mm².

m) Slump shall be 100 mm to 150 mm. High workability is to ensure concrete

can flow against the walls of bored shaft without compaction to avoid

segregation, honeycombing, bleeding and other defects. Plasticizer additive

is required to ensure W/C is about 0.50. Tremie pipe should be used even in

dry holes when concrete pouring height exceeds 2.0m. Retarder should be

added if concreting time exceeds 1 hour.

n) Works construction specification for bored piles is stipulated in KPKR

circular 6/1988 or JKR Standard Specification For Road Works.

o) Measures and precautions for bored piles installation:-

- Construction details with control/criteria to determine founding level

should be clearly specified on the drawing

- Loosening & softening of bored shaft & base should be avoided or

reduced. Drilling must be completed speedily say less than 3 hrs.

preferably. Concreting should be done immediately after cleaning the

hole & complete it within 1 hour.

- Waisting & necking could be prevented if concreting is done strictly

according to JKR specification especially when temporary casing and

tremie pipes are used. Records of concrete used per 0.5m depth and/or

sonic logging test shall be specified (1-20% of piles installed), if

waisting and necking is likely to occur.


21

- For bored piles designed to be socket in weathered fractured rock,

chiseling should be carefully controlled or chiseling is preferably

replaced by coring or reverse circulation method to avoid excessive

loosening and shatter of bedrock. It is very important to ensure the

socket is properly cleaned, as the full capacity may not be mobilized

before large settlement occur owing to the compression of any debris of

loose rock fragments, mud, etc., remaining in the base of the socket.

Method of socket construction & construction control should be clearly

specified on the drawing.

- Base grouting should be specified if high end bearing is required..

Continuous vertical core sampling is sometimes carried out to check

quality of concrete and to examine the tightness of the contact between

the base of piles and the bearing soil/rock layer.

p) Advantages and disadvantage of bored piles are as follows:-

The Advantages:

No risk of ground heave

Length can be readily varied i.e. no wastage in erratic hard strata

formation

Soil can be inspection or tested (SPT) and compared with design data.

Can be installed in very long lengths with very large diameters.

Reinforcement is not dependent on handing or driving condition where

control is difficult.

Can be installed without appreciable noise or vibration, and under

conditions of limited headroom .

The Disadvantage:

Boring methods may loosen sandy or gravelly soils especially in water

bearing strata. Bentonite contamination is a common cause of low

quality bored piles.


22

Susceptible to waisting or necking in squeezing ground and inadequate

support of wet concrete in very soft ground. In such conditions sonic

logging methods using 3 or 4 pipes should be adopted to scan the

potential defects.

Difficulties with concreting under water. The concrete cannot

subsequently be inspected.

An inflow of underground water may cause damage to the unset

concrete in the pile or may cause a disturbance to the surrounding

ground leading to reduced piles bearing capacity.

High mobilization cost (due to involvement of expensive & large

plants).

The last capacity is usually reduced by 30% to 50% or completely

ignored compared with driven displacement piles to account for the

larger settlement required to mobilize the ultimate end bearing capacity

especially when the loose and soft materials at the base cannot be

completely cleared, inspected and verified within reasonable &

practical means.

5.6 STEEL PILES

a) Usually in H – sections & cylindrical pipes. (200mm to 2000mm &

capacity of 40 tonnes to 1000 tonnes).

b) Penetration readily extended or varied (by welding); greater flexibility;

structurally (material) very superior and can stand very hard driving and

penetrating dense layers (main advantage of steel piles when compared

with concrete piles)

c) Compressive and tensile strength of steel pile are 250 N/mm² and 410

N/mm² respectively or more (Compressive and tensile strength of concrete

are only about 40 N/mm² and 4 N/mm² respectively for grade 40 concrete).

d) Toe can be strengthened or stiffened by welded-on-plates if very hard

driving is expected.

e) Usual steel grades used: Grade 43A steel (BS 4360), fy = 240 N/mm²,

Grade 50B steel (BS 4360), fy = 355 N/mm².


23

f) Max. allowable structured load = 30%fy x A, where fy = yield stress and A

= cross sectional area.

g) Corrosion needs to be considered in aggressive soil or marine conditions

(solved by epoxy coating, cathodic protection or by increasing the thickness

of pile).

Steel corrosion rate.

- In disturbed soil (pH = 2.3-8.6) < 0.01 mm/yr

- In undisturbed natural soil (>5ft): negligible

- Below sea bed = 0.01 to 0.02 mm/yr

- Immersed sea water = 0.10 mm/yr

- Splash zone = 0.15 mm/yr per surface

- In fresh water = 0.05 mm/yr

- Below river bed = negligible

- In atmosphere = 0.05 to 0.10 mm/yr

Maximum corrosion rate (BBC);

- 20mm /100yr industrial atmosphere

- 10mm/100yr normal atmosphere

- 3mm/100yr in normal soil

- 5mm/100yr in fresh water (pH=4-9)

- 25mm/100yr in splash zone

h) Standard sizes of steel piles and recommended capacity are in Appendix.

5.7 MICROPILES

a) Usually sizes 100mm, 150mm ,200mm, 300mm and 350mm diameter &

pile capacity of 200kN to 2000kN depending mainly on soil/rock

conditions and reinforcement. Max length can be up to 60m. For high

capacity long piles, elastic shortening is quite significant and bucking shall

be checked. Piles caps supported by piles of significant difference in


24

lengths may result in the shorter piles being overstressed (stress>fy). In

such case more piles have to be added to reduce working loads on piles.

b) Micropiles are low noise & little pollution pile system; suitable for under

pinning & in limestones or boulder abundant areas. Can be expensive

especially especially when permanent casing is required such as in

limestone areas with severe cavities (No casing at design bond length). Can

be designed to take compressive & tensile loads.

c) Reinforcement can be high tensile bars (or stiff cohesion soils or stable

bored shaft conditions only) or steel pipes. Structural capacity should have

a min factor of safety of 2.0.

d) Design structural capacity of micropiles Qd is the lower of:-

Qd = fy.As or Qd = 0.4 fcu.Ac + 0.75 fy.As (short column)

Where, fy = yield stress of API pipe, 552 N/mm² for Grade N80

As = area of API pipe

fcu = grade of grout

Ac = Grout area

e) For long and slender pile (slenderness ratio exceeding 120) or pile group

with significant difference in pile lengths, the max. allowable capacity is

controlled by elastic compression.

f) Micropiles capacity from bond between grout and rock depends almost

entirely on the strength of grout (fcu) and unconfined compression strength

of rock (q) as well as the quality of the contact area resulting from the

drilling, flushing and grouting processes.

Qa = Afb

Where, Qa = allowable load, kN

A = surface area of bond


25

fb = allowable bond strength

= 250-2000 kPa

= smaller of 0.05 fcu and 0.05 q;

Recommended fb for limestone bedrock:-

fb = 300 kPa for RQD<25%

= 600 kPa for RQD = 25-70%

= 1000 kPa for RQD>70%

fb recommended by BS 8081 for limestone is 0.26 to 1.18 N/mm².

g) Generally, working bond stress should be limited to about 0.6 N/mm²

unless detail rock socket conditions are known.

h) Micropiles are formed by rotary boring using temporary casing fitted with

cutting bits, augers, or tricone bits or down-the-hole percussive hammers in

rock or very hard materials. Flushing media can be air or water; but water is

preferred because it can be used for water tightness test to check cavities or

connecting channels in limestone bedrock and also less damaging in

cavities abundant bedrock.

i) After the design depth is drilled, the hole is flushed with clean water.

Cement grout (w/c = 0.45 to 0.5) with non-shrink mixture is then

immediately pumped to the bottom through tremie pipe or reinforcement

pipe. Water within the hole is displaced until clean grout oozes out.

Reinforcement bars if applicable are then carefully inserted and temporary

casing slowly withdrawn (usually). The grout level is checked and

maintained as the casing is withdrawn. This is to prevent necking and

collapse of the bored shaft. The performance of micropiles depends very

much on processes of drilling, flushing and grouting as well as the

verticality of the pile alignment. Load tests should be carried out after a

lapse of minimum 7 days and when grout strength has achieved the design

strength.


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24

6. BEARING CAPACITY OF PILES

The bearing capacity of piles depends mainly on the type of soil though which

and /or which it rests, and on the method of installation. It also depends on the

piles material, pile perimeter or surface areas and length of the piles.

JKR Building specification the failure load of load of piles as that which cause

a settlement of 10% of the size or 38mm whichever is the less. Experience has

shown that if a safety factor of 2 to 3 is applied to the failure load the

settlement at working load is unlikely generally to exceed 12mm (0.5 in)

which is the normal tolerable settlement for R.C framed structures.

The ultimate load on a pile is the load that can cause failure on either the pile

or the soil ; but in most situations, the ultimate load (Qu) is determined by the

soil failure which means punching shear at veering (Qp) preceded by direct

shear failure along the shaft (Qs). The movement (settlement) required to

mobilized the max shaft resistance is in the order of 0.3 to 1% piles of size

(typically 5 to 10mm) while that for point resistance is 10 to 20% (Tomlinson

1987). Where appropriate, allowance may be made for the elastic (BS8004),

especially for high capacity slender piles socket in rock.

Bearing capacity of piles (unit shaft friction fs & unit point resistance of (q)

have been successfully predicted using the following empirical formula:

The ultimate bearing capacity of a pile shall be determined by one but

preferable two or more of the following:

i) Static formula based on adequate SI results

ii) Dynamic formula based test (JKR standard methods)

iii) Typical presumed bearing values of soils and rocks (BS 8004 Table 2).

Ultimate unit skin resistance fs and bearing of piles, of shall be estimated on

the following basis

:


11.7.2017

25

i) Lab or in situ test on undisturbed samples on soil and rock

ii) Pile test loading results

6.1 UNIT SHAFT RESISTANCE (fs)

fs = N/50 Tsf

= 2N kPa

< 100 kPa, for driven or bored piles in residual or cohesive soils.

N = Standard Peneteration Test (SPT)

fs = Cu (Tomlinson, 1987), for driven piles in clay, Cu from vane shear

tests etc.

= 1 for Cu 25 kPa

= 0.5 to 1.0 for Cu = 25-75 kPa (firm to stiff)

= 0.3 to 0.5 for Cu 75 kPa (stiff to hard)

fs = K tan . v

< 100 kPa, for cohesionless soil

K = 1 for full displacement piles

= 0.8 for partial displacement piles

= 15 very loose sand

= 20 loose sand

= 25 medium dense sand

= 30 dense or very dense sand

v = vertical effective stress adjacent to the pile

fs = 0.05 Ckd, for sand, Ckd = cone resistance

fs = 1/36 Ckd, for soft to stiff clay

Ckd = cone resistance from Static Dutch Cone Test


11.7.2017

26

6.2 UNIT POINT RESISTANCE (q)

q = KN (Tsf)

< 100 Tsf

N = SPT value

K = 2.0 for clay

= 2.5 for silt

= 4.0 for sand

= 1.0 for bored piles

q = Ckd (Tsf)

< 100 Tsf

Ckd = cone resistance

q = 9 Cu , for piles in clay

Cu = cohesion of clay

6.3 ESTIMATION OF NEGATIVE SKIN FRICTION

Negative friction or downdrag will whenever the adjacent soil settles more

than the piles.

i) When the relative displacement of pile and the soil greater than 5 to 10,

the unit negative friction.:

M= k Po (BB Broms)

Where, Po = effective overburden pressure.

k = 0.20 for n-c clay with PI > 50%

k = 0.30 for silt and n-c clay with PI > 50%

k = 0.35 for sand & gravel

k = 0.40 for rock fill

ii) To reduce negative skin friction , the following measures have been

used ;

a. Coating the piles with bitumen or other viscous coating


11.7.2017

27

b. Driving piles inside a casing with space between pile and casing

with drawn.

iii) When the rate of relative movement is small Bjerrum suggested that

the unit negative friction ,

fn = kPo

where k = 0.25 for very silty clay

k = 0.20 for low plasticity clays

k = 0.15 for clays of medium plasticity

k = 0.10 for highly plastic clays

iv) Negative friction or down drag load live load shall not be considered

together. (DL + NF or DL + LL) . The neutral plane where negative

friction (NF) changes to positive shaft resistance. If the pile settlement

under working conditions is sufficient to reduce the effect of negative

friction ,

Qa = (Qu –NF )/ FOS

6. 4 SETTLEMENT OF SINGLE PILES

The actual load-settlement characteristics of a single pile is a function of the

relative contribution of skin friction and end of the relative contributions of

skin friction and end bearing , the soil conditions and method of installation

.For normal load levels. (not too near or too far from failure load), the

settlement of piles can be estimated from the empirical formula given by

Vesic (1970, 1977)

S = b + QL

100 AE

Where, S = settlement of piles load

b = pile diameter

Q = applied load

A= average sectional area of pile


11.7.2017

28

L= total pile length

E= modulus of elasticity of pile material

6.5 LATERIAL CAPACITY OF PILES

When the lateral load or moment is imposed on pile, the pile will deflect until

the lateral reaction in the surrounding soil is mobilized.

The lateral capacity of piles are limited in 3 possible cases:

i) The pile material may fail due to excessive bending from lateral load

moment

ii) The pile head may deflect excessively and not acceptable to the

superstructure

iii) The surrounding soil may fail due to excessive deflection of pile as a

result of lateral load

6.6 PILE GROUP ANALYSIS

Pile installation operation can change adjacent soil properties and has

significant influence on pile response to load and load-settlement

characteristics. Methods of computing pile group capacity and settlement in

cohesive & cohesionless soils have been well presented by Tomlinson (1987)

and frequently used by JKR engineers to predict pile group capacity.

Settlement for big pile groups (more piles per group) consisting of pre

dominantly frictional piles must be checked for “Block Failure”.

Generally for small pile groups with pile spacing exceeding 2.5 pile size and

predominantly end bearing the ultimate load of pile group can be taken to be

equal to the sum of ultimate load of individual pile. Settlement of pile group

consisting of predominantly end bearing piles can be estimated by Skempton’s

method:-


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Settlement of pile group = s

Where s = settlement of single pile from load test

depends on ratio of group width B to pile size D.

B/D = 1 5 10 20 40 60

= 1.0 3.5 5.0 7.5 10 12

For pile groups in cohessionless soil, empirical method by Vesic (1970) can be

used:-

Sg/Ss = (B/b)0.5

Where, B = width of pile group

b = pile size

7.0 LOAD TESTS

Due to many approximations and uncertainties in the analysis, full scale load

test up to 2 times of the design load to verify the actual pile response to load

especially actual settlement characteristics is a must for all JKR projects. The

elapsed time between diving or installation and testing should be minimum 7

days for end bearing piles and 28 days for frictional piles. As a rule of thumb,

the rule of at least one load test every 50 to 100 piles can be used as a guide in

normal consistent or familiar subsoil conditions. In erratic subsoil where

driving resistance or penetration varies considerably the number of piles tested

should be sufficient to represent the range of condition encountered.

For JKR Building projects, the maximum load test is twice the design load and

the pile so tested shall be deemed to have failed if:-

i) The residual settlement removal of the test load exceeds 6.35

mm (0.25‘)

ii) The total settlement under design load exceeds 12.5 mm ( 0.5”)

iii) The total settlement under twice the design load exceeds 10%

of pile size or 38.1 mm (1.5”) or exceed 0.25 mm per ton of test

load whichever is the lowest value.


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The above load test acceptance criteria must be evaluated carefully and the

following uncertainties in load test result shall be borne in mind:-

a) Single pile load test do not indicate group capacity. This must be

evaluated analytically or by experience.

b) Load test do not normally evaluate long term effects such as soil

relaxation, creep or negative fiction caused by subsiding soil.

Environmental effects on pile material are also not accounted for.

Other factors that may influence the interpretation of load test results are:-

a) Potential residual loads in the pile, which may influence the interpreted

distribution of load at the pile tip and pile shaft.

b) Potential loss of supporting test pile from such thing as excavation and

scouring.

c) Requirement that all conditions for non-tested working piles be

basically identical to those for test pile including such thing as subsoil

conditions, pile type, length, size and stiffness and pile installation

methods and equipment piling frame and hammer so that application or

extrapolation or extrapolation of the test results to such other piles is

valid.

Pile Driving Analyzer (PDA) is useful to check the driving stress & structural

integrity; but can no way replace full scale load test in respect of checking

settlement characteristics. Though PDA (TNO or CAPWAP) and other sonic

tests are quick and cheap methods to scan for potential defects of piles in

general.

Ultimate pile load and structural conditions can also be evaluated using Chin

F.K’s Method.

Construction control for working piles shall be based on analysis of

preliminary load test results and driving records.


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When a load test fails, detailed investigation with particular reference to load-

settlement characteristics of test pile, installation records, loading procedure

and measurements, instrument calibration records, soil investigation results

and design parameters etc. shall be carried out to identify the cause of failure.

Capacity of working piles (if any) that have similar installation history to the

failed test pile should be reviewed and then the design and or construction

control amended accordingly. It is important to ascertain whether the failure is

due to structural or geotechnical factors. For geotechnical factors, the pile

capacity have to be downgraded or lengthened. For structural factors, the

review of piling system or construction control shall be carried out.

Notes on Maintained Load Test

The load shall be applied in increments of 25% of the working load, up to the

working load and appropriately smaller thereafter, until a maximum test load

of twice the working load is reached. Each increment of load shall be applied

as smoothly as expeditiously as possible. Settlement readings and time

observations shall betaken before and after each new load increment.

A time-settlement graph shall be plotted to indicate when the rate of settlement

of 0.05mm in 15 minutes is reached. A further increment of load shall be

applied when this rate of settlement is achieved or until a minimum time of 2

hours has elapsed, whichever is later. The process shall be repeated until the

maximum test load is reached.

The maximum test load shall then be maintained for a minimum of 24 hours,

and time-settlement readings shall be taken at regular intervals as for the

earlier load stages.

The test load shall then be decreased in four equal stages and time-settlement

readings shall be as described aforesaid until the movement ceases. At least 60

minutes shall be allowed between the unloading decrements.


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The contractor shall, within 24 hours of the completion of the test, submit to

the Engineer a complete record of each pile test, including,

i) A graph of load and movement plotted above and below a common

base line of time.

ii) A graph of movement and recovery plotted vertically below a

horizontal axis of load.

The pile so tested shall be deemed to have failed if:

i) The total settlement under twice the design load exceeds 38mm (1.5”)

or 10% of the pile size, whichever is the lower value; or

ii) The total settlement under the design load exceeds 12.5mm; or

iii) The permanent or residual settlement after removal of the test load

exceeds 6.5mm (0.25”).


33

LOAD-TIME GRAPH

TIME

LOAD-SETTLEMENT GRAPH

SETT LEMENT

LOAD

LOAD

Smax Smax

Sd

Pd 2Pd

PRESENTATION OF PILE LOADING TEST RESULTS


34

8.0 THE HILEY FORMULA

The Hiley formula takes into account energy losses occurring in the hammer

system, at the point of impact and due to compression of the head assembly

(dolley, helmet, packing), the pile and the surrounding ground. The energy

considerations are as follows:-

a) The energy at impact at impact from a weight W falling a distance H is KWH

where K ia a constant which takes into account frictional loss in the hammer

system.

b) The energy required to drive the pile a distance s against a driving resistance

R is Rs

c) The energy loss at impact between the hammer and the pile head assembly is

KWHP(1 – e2)

(W + P)

where, P is the weight of the pile and

e is the coefficient of restitution

d) The energy loss due to elastic compression cc, cp and cq in the pile head

assembly, pile, and ground, respectively, is ½ R(cc + cp + cq)

Thus, the energy equation is:-

KWH = KWHP(1 – e2) + Rs + ½ R(cc + cp + cq)

(W + P)

Rearranging gives the more usual form of the formula:-

R = WH where = k(W + e2 P)

s + ½ c (W + P)


35

and c = (cc + cp + cq)

The rebound of the pile and ground (cc + cp) can be measured by fixing a straight

edge, anchored to the ground by stakes, alongside the pile and moving a pencil

slowly along it during driving so that it marks a piece of card which is attached to

the pile. From the plot (Figure 1) the value of (cc + cp) can be directly measured.

Mampatan elastik (cp + cq)

Set (s)

Figure 1- Measurement of elastic rebound of a pile

Set (s) = 0

Figure 1.1- Measurement of set for pile driven to refusal during driving

Earth surface

pile

pencil

Graph paper fixed to the pile

Timber blok

Figure 1.2- Simple method for taking pile set on site


36

Table 1 - Value of hammer coefficient K

Hammer K

Drop hammer, winch operated 0.8

Drop hammer, trigger release 1.0

Single-acting hammer 0.9

BSP double-acting hammer 1.0*

McKiernan-Terry diesel hammers 1.0**

* Instead of WH in Hiley formula use manufacturers rated energy per blow, at actual speed of operation of hammer, the hammer speed must be checked when taking the final set.

** For WH substitute manufacturer’s rated energy per blow, corresponding to the

stroke of the hammer at the final set.

Table 2 - Values of the coefficient of restitution, e.

Type of pile Head condition Single-acting or

drop-hammer or

diesel hammer

Double-

acting

hammer

Reinforced

Concrete

Helmet with composite plastic or Greenheart

dolly, and packing on top of pile

0.4 0.5

Helmet with timber dolly (not Greenheart)

and packing on top of pile

0.25 0.4

Hammer directly on pile with pad only - 0.5

Steel Driving cap with composite plastic or

Greenheart dolly

0.5 0.5

Driving cap with timber (not Greenheart)

dolly

0.3 0.3

Hammer directly on pile - 0.5

Timber Hammer directly on pile 0.25 0.4


37

Efficiency

Of blow,

0.8

0.7

0.6

0.5

0.4

0.3

0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

P/W

Figure 2: Determination of efficiency factor, , for use in Hiley pile driving formula, after

BSP Pocket Book (1969)

10

9

8

7

6

5

4

3

2

1

0 5 10 15 20 25

Overall driving stress = Ru (MN/m2)

Overall pile area

Figure 3: Determination of temporary elastic compression Cc, after BSP Poket Book (1969)

Key, A= concrete pile, 75mm packing under helmet; B= concrete or steel pile,

helmet with dolly or head of timber pile; C= 25mm pad only on head of RC pile

A

B

C

Cc (mm)

e=0.5

e=0.4

e=0.3

e=0.25


38

25

20

15

10

5

0 5 10 15

Actual driving stress = Ru (MN/m2)

Actual pile area

Figure 4: Determination of temporary elastic compression Cp, for concrete piles, after BSP

Poket Book (1969)

25

20

15

10

5

50 100 150 200


Actual pile area

Figure 5: Determination of temporary elastic compression Cp, for steel piles, after BSP

Poket Book (1969)

Pile length = 25m 20m

15m

10m

Cp

(mm)

Pile length = 30m

20m

15m

10m

Cp

(mm)

25m


39

20

15

10

5

0 5 10 15


Actual pile area

Figure 6: Determination of temporary elastic compression Cp, for timber piles, after BSP

Poket Book (1969)

6

5

4

3

2

1

0 5 10 15 20 25

Overall driving stress = Ru (MN/m2)

Overall pile area

Figure 7: Determination of temporary elastic compression Cq, after BSP Poket Book (1969)

Pile length = 15m

10m

5m

Cp

(mm)

Cq

(mm)

guideline for piling works -...

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