development of geotechnical codes - intro.pdf · 2017-11-17 · 03/11/2017 3 codes v standards in...

03/11/2017

1

SAICE Geotechnical Division

Development of Geotechnical Codes

Peter Day02 November 2017

Geo

tech

nica

l Des

ign

Cod

es

GEOTECHNICAL DIV IS IONSouth African Institution of Civil Engineering

Why are we here – what is our objective?

Three new design codes required:• geotechnical design• piling• lateral support

Objective: To decide collectively the form these codes should take

Geo

tech

nica

l Des

ign

Cod

es

03/11/2017

2

Outline:• Codes v Standards• How standards are written ?• Status of codes and standards• Cross-discipline and international harmonisation• Existing South African design codes• International practice• Options for SA geotechnical design standards• Comparison of design methodsG

eote

chni

cal D

esig

n C

odes

Outline:• Codes v Standards• How standards are written• Status of codes and standards• Cross-discipline and international harmonisation• Existing South African design codes• International practice• Options for SA geotechnical design standards• Comparison of design methodsGeo

tech

nica

l Des

ign

Cod

es

03/11/2017

3

Codes v Standards

In the context of design standards:

Standards = Codes of Practice

For example:

• The Eurocodes are European standards

• SANS 10160 (Loading code) is a South African standard

• SAA Loading Code is an Australian standard

Cod

es v

Sta

ndar

ds

code of practice (n) (plural codes of practice).

a set of guidelines and regulations followed by members of a profession, trade, occupation, organization etc.

(source: wiktionary)

Based on best current practice in the industry – not the state of the art.

Cod

es v

Sta

ndar

ds

03/11/2017

4

Outline:• Codes v Standards• How standards are written ?• Status of codes and standards• Cross-discipline and international harmonisation• Existing South African design codes• International practice• Options for SA geotechnical design standards• Comparison of design methodsG

eote

chni

cal D

esig

n C

odes

Writ

ing

of S

tand

ards

National Standards (e.g. SABS) Industry Standards (e.g. SAICE)

03/11/2017

5

National Standards

• SABS standards have automatic credibility

• Written by volunteers with no remuneration or recognition

• Responsibility for content rests with Technical Committees

• SABS does administration and distribution only

• Initiated by a “New Work Item Proposal”

• Code written by working group from the profession and academia

• Formal approval process (Committee Draft, DSS, Public Comment)

• Consensus documents Consensus = absence of sustained opposition (SANS 1)W

ritin

g of

Sta

ndar

ds

Technical Committeee.g. TC98 – Structural and

Geotechnical Design Standards

Subcommitteee.g. TC98 SC03 -

Geotechnical Design Standards

Working Groupse.g. WG 01: Geotechnical

Design

Writ

ing

of S

tand

ards Subcommittee

e.g. TC98 SC01 – Basis of Structural Design and

Actions

Chair: Peter Day

Chair: SABS

Chair: Alan Parrock

03/11/2017

6

Outline:• Codes v Standards• How standards are written• Status of codes and standards• Cross-discipline and international harmonisation• Existing South African design codes• International practice• Options for SA geotechnical design standards• Comparison of design methodsG

eote

chni

cal D

esig

n C

odes

Stat

us o

f Cod

es a

nd S

tand

ards

Standards are not mandatory unless:

• Referred to in applicable legislation

• Required to fulfil Local Authority or NHBRC requirements

• Specified by contract

03/11/2017

7

Pro

fess

iona

l Obl

igat

ions

Error ?

Negligence ?

Stat

us o

f Cod

es a

nd S

tand

ards

Pro

fess

iona

l neg

ligen

ce

Norms of the profession

• Norms in the profession established by• Standard forms of agreement (if no formal

contract)• Scope of services and schedules of tariffs• Professional codes of conduct• Codes and standards• Expert testimony

Increasing relevance

Stat

us o

f Cod

es a

nd S

tand

ards

03/11/2017

8


eote

chni

cal D

esig

n C

odes

Har

mon

isat

ion

Courtesy: Bernt Schuppener

03/11/2017

9

Structural engineer:

! 1

,,1,1,1

,, """"i

ikiiQkQj

jkjG QQG

Geotechnical engineer:

F ?? please !!

Har

mon

isat

ion

Bernd Schuppener on the evolution of standards

Har

mon

isat

ion

03/11/2017

10


eote

chni

cal D

esig

n C

odes

Existing Geotechnical Design Codes

• SANS 0161:1980 Design of foundations for buildings

• SANS 088:1972 Piled foundations

• SANS 10160-5:2011 Basis for geotechnical design and actions

• SANS 207:2011 Design, construction of reinforced soils and fills

• SAICE 1989 Lateral support in surface excavations

• EN1997-1:2004 Geotechnical design – general rulesExis

ting

Des

ign

Cod

es

03/11/2017

11

Exis

ting

Des

ign

Cod

es

SANS 10160-5

Exis

ting

Des

ign

Cod

es

SANS 10160-5• Limit states design code

• Basis of design and actions only

• Based on SANS 10160-1 (basis of structural design)

• Fully compatible with Eurocodes

• Can be used in conjunction with EN1997-1

• Does not cover:• Slopes and embankments• Retaining walls and lateral support• Piles

03/11/2017

12

Exis

ting

Des

ign

Cod

es

Eurocode 7 - EN1997-1:2004• Based on EN1990 and ISO 2394

• Covers:• Fill, dewatering ground improvement and

reinforcement• Spread footings• Piled foundations• Anchorages• Retaining structures• Hydraulic failure• Overall stability• Embankments

• Based on EN1990 and ISO 2394

• Covers:• Fill, dewatering ground improvement and

reinforcement• Spread footings• Piled foundations• Anchorages• Retaining structures• Hydraulic failure• Overall stability• EmbankmentsEx

istin

g D

esig

n C

odes

Eurocode 7 - EN1997-1:2004

SANS 207 / BS 8006

SAICE 1989 – WSD only

03/11/2017

13


eote

chni

cal D

esig

n C

odes

International Codes

Europe Eurocodes Limit states design

North America ASCE, AASHTO … Load and resistance factor design

Japan Local Performance based design

Australia AS Limit states design

International ISO 2394 General principles of reliability

Inte

rnat

iona

l Cod

es

03/11/2017

14


eote

chni

cal D

esig

n C

odes

Working stress design (global FoS)• Familiar and simple to use

• Fundamentally flawed

• FoS poor measure of reliability

• Focuses mainly on resistance

Limit states design• Current international norm

• Artificial distinction between ULS and SLS

• Perceived complexity, multiple design approaches

• Partial factors somewhat arbitrary

• Subjective selection of characteristic values

Mobilised strength design• Design based on acceptable strains not limiting

stresses

• Still under development

• Undrained soils only

Reliability-based design• Accounts directly for uncertainty at source

• Can be used to complement to LSD

• Computes and pf directly

• Difficult for “non closed-form” problems e.g. slopes

• Requires statistical characterisation of parametersOpt

ions

for S

A C

odes

03/11/2017

15

Mobilised strength design• Design based on acceptable strains not limiting

stresses

• Still under development

• Undrained soils only

Opt

ions

for S

A C

odes

Appropriate strain design• Parrock and O’Brien

• Design based on acceptable strains not limiting stresses

• Applies to c’ ’ soils

• Still being developed – not current practice

Do not miss the next lecture!

Working Load Design

Re sis tanceFOS

Load

“Devils”“Angels”

or

Opt

ions

for S

A C

odes

03/11/2017

16

Working Load Design

• Self weight – Angel or Devil?

WLD v LSD

Resisting

Activating

Opt

ions

for S

A C

odes

Limit States Design

• ULS Verification:

• Provision for safety is in selection of design values either statistically or by partial factors

dd RE Design action effect Design resistance

Opt

ions

for S

A C

odes

03/11/2017

17

If H = W R1 = W R2 = 0

No anchor required at R2 for any FOS !

L/2

L

HW

Opt

ions

for S

A C

odes

L/2

L

1.35 H0.9 W

If H = W R2 = -0,35W (uplift)

Anchor is required at R2 !Opt

ions

for S

A C

odes

03/11/2017

18

Ferrybridge cooling towers,1st November 1965

Opt

ions

for S

A C

odes

Overview of Design Methods

Deterministic Methods Probabilistic Methods

Opt

ions

for S

A C

odes

SANS 10160

What the code-writer doesTraditional design methods• Slope stability• Bearing capacity• Earth pressure• etc.

JV Retief, based on EN1990

03/11/2017

19



Opt

ions

for S

A C

odes

JV Retief – based on EN1990

SANS 10160-5

What the code-writer doesWhat the designer does



Opt

ions

for S

A C

odes Becoming more achievable

on a practical level

03/11/2017

20

Opt

ions

for S

A C

odes

0,6m

L = B = ?

W = Wind load

G = dead load of superstructure plus conveyor

7,0m

V-0.8m

Parameter Distribution Para1 Para2

G Dead Load Normal V 1000 50

Q Live Load Lognormal W 0.001 0.001

W Wind Load ExtValue1 Z 200 70

Phi Lognormal Z 34.5 3.5

Cohesion Lognormal Z 3.8 1.5

Added ex Normal Z 0.001 0.061

4 xi* n i g(x)

988.1776 1 0 0 0 0 0 -0.236 8E-09 2.8276

0.000707 0 1 0 0 0 0 -4E-06

492.005 0 0 1 0 0 0 2.7868 Probability of Failure

33.00576 0 0 0 1 -0.25 0 -0.387 0.00234

3.529646 0 0 0 -0.25 1 0 -0.004

0.007999 0 0 0 0 0 1 0.1147

Correlation matrix [R]

Opt

ions

for S

A C

odes

Variables

Input parameters

Low & Tang, 2007

03/11/2017

21

Parameter Distribution Para1 Para2

G Dead Load Normal V 1000 50

Q Live Load Lognormal W 0.001 0.001

W Wind Load ExtValue1 Z 200 70

Phi Lognormal Z 34.5 3.5

Cohesion Lognormal Z 3.8 1.5

Added ex Normal Z 0.001 0.061

4 xi* n i g(x)

988.1776 1 0 0 0 0 0 -0.236 8E-09 2.8276

0.000707 0 1 0 0 0 0 -4E-06

492.005 0 0 1 0 0 0 2.7868 Probability of Failure

33.00576 0 0 0 1 -0.25 0 -0.387 0.00234

3.529646 0 0 0 -0.25 1 0 -0.004

0.007999 0 0 0 0 0 1 0.1147

Correlation matrix [R]

Opt

ions

for S

A C

odes

Your favouritebearing capacity spreadsheet

fq qInput

1min T

x Fn R n

Outline:• Codes v Standards• How standards are written• Status of codes and standards• Cross-discipline and international harmonisation• Existing South African design codes• International practice• Options for SA geotechnical design standards• Comparison of design methodsGeo

tech

nica

l Des

ign

Cod

es

03/11/2017

22

Method of Evaluation

• 7 simple structures

• One soil type

(Orr, 2005)

(sand, ’k = 32o, k = 20kN/m3)

Com

paris

on o

f Met

hods



• One soil type

• Find Eurocode-compliant solution

(Orr, 2005)

(sand, ’k = 32o, k = 20kN/m3)

(DA1-C2)

Com

paris

on o

f Met

hods

03/11/2017

23



• One soil type

• Find Eurocode-compliant solution

• Determine and pf

• Calculate FoS

• Repeat for range of parameters values & CoVs

(Orr, 2005)

(sand, ’k = 32o, k = 20kN/m3)

(DA1-C2)

(FORM and Monte Carlo)

(using mean & characteristic values)

Com

paris

on o

f Met

hods

Footings Single pile Retaining walls

A

B

C

DE

F

G

B = ?

L = B = ?

L = B = ?

Strip

Pad

Pad

L = ?B = ?

Z = ?

Z = ?

Com

paris

on o

f Met

hods

03/11/2017

24

Soil Type:

Non-cohesive sand:

’k = 32o, log-normal, CoV=10%

k = 20kN/m3, normal, CoV=5%

, = 0.2

Loading:

• Gk fixed value, = mean

• Qk log-normal CoV = 25%

• Wk Gumbel CoV = 50%

Com

paris

on o

f Met

hods

1 or 1

kk k v

k v

xx x c x

c

Retief & Dunaiski (2010)Phoon & Kulhawy (1999)

Schneider (1997)

Com

paris

on o

f Met

hods

03/11/2017

25

Example FORM M/C Mean Char

A. Strip vertical load 3.49 3.45 5.18 2.50

B. Square vertical load 3.51 3.46 4.86 2.40

C. Square inclined load 3.69 3.58 6.58 2.60

D. Pile 3.36 3.35 2.76 1.73

E. Gravity wall 3.33 3.3 6.88 3.12

F. Cantilever wall 3.40 3.39 2.34 1.63

G. Anchored wall 3.24 3.23 1.43 1.25

Reliability Index

Findings:Global Factor of Safety

Good agreement between FORM and Monte CarloDe Koker & Day (2017)C

ompa

rison

of M

etho

ds





D. Pile 3.36 3.35 2.76 1.73

E. Gravity wall 3.33 3.3 6.88 3.12


G. Anchored wall 3.24 3.23 1.43 1.25

Reliability Index


Remarkable consistency across all examplesDe Koker & Day (2017)C

ompa

rison

of M

etho

ds

03/11/2017

26





D. Pile 3.36 3.35 2.76 1.73

E. Gravity wall 3.33 3.3 6.88 3.12


G. Anchored wall 3.24 3.23 1.43 1.25

Reliability Index


Close to target of = 3.2 - 3.8De Koker & Day (2017)C

ompa

rison

of M

etho

ds





D. Pile 3.36 3.35 2.76 1.73

E. Gravity wall 3.33 3.3 6.88 3.12


G. Anchored wall 3.24 3.23 1.43 1.25

Reliability Index


Wide variation in FoSCom

paris

on o

f Met

hods

03/11/2017

27

De Koker & Day (2017)

Rel

iabi

lity

Inde

x

4.5

4

3.5

3

2.525 30 35 40

Mean friction angle ’ (deg)

FootingsABC

PileD E

FG

Retaining

CoV ' = 0.1

3.2

–3.

8

approx. in target range(except for pile example)

12

8

10

4

6

25 30 35 40Mean friction angle ’ (deg)

Glo

bal F

oS (M

ean

valu

es)

0

2

FootingsABC

PileD E

FG

Retaining

Wide variation in FoS

1.4

-10

Com

paris

on o

f Met

hods

Acceptable range 2.5 – 3.0


Rel

iabi

lity

Inde

x

4.5

4

3.5

3

2.525 30 35 40


12

8

10

4

6

25 30 35 40Mean friction angle ’ (deg)

Glo

bal F

oS (M

ean

valu

es)

0

2

CoV ' = 0.1

Example C

Com

paris

on o

f Met

hods

03/11/2017

28


Rel

iabi

lity

Inde

x

4.5

4

3.5

3

2.525 30 35 40


CoV ' = 0.1

Example C

25o 40o

Smaller footingDecreased Vk

Constant Hk , Mk

Increased eccentricity

e = Mk/Vk

= atan (Hk/Vk)Fixed values for LSD

Com

paris

on o

f Met

hods

CoV CoV

Target valuefor South Africa

OK Caution

Com

paris

on o

f Met

hods

03/11/2017

29

Simpson (2007), Vogt & Schuppener (2006)B?

3.0 mGV,k = 400kN

QH,k (variable)Soil Properties:(Characteristic values)

3

' 32.5' 0 kPa

19 kN/m

ok

k

k

c

1.0 m

Comparison of Design Approaches

Com

paris

on o

f Met

hods

k kH V

Wid

th B

(m)

Comparison of Design Approaches

De Koker & Day (2017b)Simpson (2007)Com

paris

on o

f Met

hods

03/11/2017

30

log

p f

Rel

iabi

lity

Inde

x

k kH V

Target valuefor South Africa

De Koker & Day (2017b)

Findings

• Limit state design yields consistent reliability over wide ranges

• Study has vindicated the selection of DA1-C2 in SANS 10160-5

• RBD can be readily implemented for closed-form problems

• Options available for non-closed form solutions

• FORM analysis will suffice in most cases

• More work required on piles – review resistance factors

Com

paris

on o

f Met

hods

03/11/2017

31

Where to from here ?

Phot

o: R

icha

rd P

uchn

er

Where to from here ?

• Listen to the presentations

• We then need to decide:• National SABS v. Industry Standards (in each case)• Methods of design to be used• Adoption of the Eurocodes v. writing new SA standards• Are execution standards required e.g. piling, lateral support ?

03/11/2017

32

Thank you

development of geotechnical codes - intro.pdf · 2017-11-17 · 03/11/2017 3 codes v standards in...

Documents