Geotechnical Eurocodes – preparing for impact · EN 1536: 1999 Bored piles. 4 BGA – 10 October 2007 – Geotechnical Eurocodes – preparing for impact 7 Outline of EC7 Part 1

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BGA – 10 October 2007 – Geotechnical Eurocodes – preparing for impact1

Geotechnical Eurocodes – preparing for impact

Brian Simpson

Arup Geotechnics


The Eur ocode syst em BP72.9 BP106.3 BP111.4 BP112.4 BP124-T1.9 BP124-A1.9The Eurocode system (CEN-TC250)

EN 1990 Eurocode 0 Basis of designEN 1991 Eurocode 1 Actions on structuresEN 1992 Eurocode 2 Design of concrete structuresEN 1993 Eurocode 3 Design of steel structuresEN 1994 Eurocode 4 Design of composite steel

and concrete structuresEN 1995 Eurocode 5 Design of timber structuresEN 1996 Eurocode 6 Design of masonry structuresEN 1997 Eurocode 7 Geotechnical designEN 1998 Eurocode 8 Design of structures for

earthquake resistance.EN 1999 Eurocode 9 Design of aluminium alloy structures

Other related EN documents on construction, materials, etc

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EN1990 Ulti mate li mit states BP87.48 BP106.14 BP111.8 BP112.10 BP124-T1.41 BP124-A1.41EN1990 3.3 Ultimate limit states

(4)P The following ultimate limit states shall be verifiedwhere they are relevant :– loss of equilibrium of the structure or any part of it,

considered as a rigid body ;– failure by excessive deformation, transformation of the

structure or any part of it into a mechanism, rupture,loss of stability of the structure or any part of it,including supports and foundations ;

– failure caused by fatigue or other time-dependenteffects.

Serious failures involving risk of injury or major cost.

Must be rendered very unlikely. An “unrealistic” possibility.


EN1990 Servi ceabi lity li mit states BP87.49 BP106.15 BP111.9 BP112.11 BP124-T1.42 BP124-A1.42

Inconveniences, disappointments and more manageable costs.

Should be rare, but it might be uneconomic to eliminate then completely.

EN1990 3.4 Serviceability limit states

(1)P The serviceability limit states shall be those that concern:– the functioning of the structure or structural members

under normal use ;– the comfort of people ;– the appearance of the construction works.

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BS EN 1997-1:2004 Eurocode 7: Geotechnical design

• Part 1: General rules

• 12 sections• Annexes A to J• National Annex to Part 1

• Part 2: Ground investigation and testing

• 6 sections• Annexes A to X• National Annex to Part 2


Euronorms – Execution of special geotechnical works

Vertical drainageEN15237: 2007

Ground treatment by deep vibrationEN14731: 2005

Deep mixing - CorrigendumEN14679: 2006

Deep mixingEN 14679: 2005

Reinforced fill - CorrigendumEN14475: 2006

Reinforced fillEN 14475: 2006

MicropilesEN 14199: 2005

Jet groutingEN 12716: 2001

GroutingEN 12715: 2000

Displacement pilesEN 12699: 2000

Sheet-pile wallsEN 12063: 1999

Diaphragm wallsEN 1538: 2000

Ground anchors - CorrigendumEN 1537: 1999

Ground anchorsEN 1537: 1999

Bored pilesEN 1536: 1999

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Outline of EC7 Part 1 BP106.11 BP111.10 BP112.12 BP124-T1.44

BP124-A1.44

1 General2 Basis of geotechnical design3 Geotechnical data4 Supervision of construction, monitoring and maintenance5 Fill, dewatering, ground improvement and reinforcement6 Spread foundations7 Pile foundations8 Anchorages9 Retaining structures10 Hydraulic failure11 Overall stability12 Embankments

Annexes A to J


• For actions (=loads) F:

Design value =characteristic value * γF

Fd = Fk * γF

• The effects of design actions are design action effects, Ed. (Bending moments, internal forces, displacements, etc.)

• For material strengths X:

Design value = characteristic value / γm

Xd = Xk / γm

• For “resistances” R:

Rd = Rk / γR

γE E{γF Frep; Xk/γM; ad} = Ed ≤ Rd = R{γF Frep; Xk/γM; ad}/γR

Characteristic values and ULS design values BP106.18

BP111.11 BP112.13 BP124-T1.46 BP124-A1.46

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2.4.7.3.3 Design resistances [ULS] BP124-T2.8 BP124-A2.6

2.4.7.3.3 Design resistances

(1) Partial factors may be applied either to ground properties (X) or resistances (R) or to both, as follows:

Rd = R{γF Frep; Xk/γM; ad} (2.7a)

or

Rd = R{γF Frep; Xk; ad}/γR (2.7b)

or

Rd = R{γF Frep; Xk/γM; ad}/γR (2.7c)

γE E{γF Frep; Xk/γM; ad} = Ed ≤ Rd = R{γF Frep; Xk/γM; ad}/γR

Three different “Design Approaches”


Partial factors recommended in EN1997-1 Annex ABP111.20 BP129.46 BP145a. 5

Design approach is

a national choice

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Partial factors for DA1 – UK National Annex BP111.20 BP124-T2.13

BP124-A2.11 BP143.22

Values of partial factors recommended in EN1997-1 Annex A

Design approach 1 Combination 1---------------- Combination 2 ----------------Combination 2 - piles & anchorsA1 M1 R1 A2 M2 R1 A2 M1 or … M2 R4

Actions unfav 1,35favunfav 1,5 1,3 1,3

Soil tan φ' 1,25 1,25Effective cohesion 1,25 1,25Undrained strength 1,4 1,4Unconfined strength 1,4 1,4Weight density

Spread Bearing EC7footings Sliding valuesDriven Base 1,7/1.5 1,3piles Shaft (compression) 1.5/1.3 1,3

Total/combined 1.7/1.5 1,3Shaft in tension 2.0/1.7 1.6

Bored Base 2.0/1.7 1,6piles Shaft (compression) 1.6/1.4 1,3

Total/combined 2.0/1.7 1.5Shaft in tension 2.0/1.7 1.6

CFA Base As 1.45piles Shaft (compression) for 1.3

Total/combined bored 1.4Shaft in tension piles 1.6

Anchors Temporary 1,1 1,1Permanent 1,1 1,1

Retaining Bearing capacitywalls Sliding resistance

Earth resistanceSlopes Earth resistance

indicates partial factor = 1.0

C:\BX\BX-C\EC7\[Factors.xls]

Permanent

Variable


Design Approach 1

• The most consistent approach for ULS

• All designs must comply with both combinations in all respects, both geotechnical and structural

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8m propped wall BP87.71 BP111.33 BP115.51


8m propped wall BP87.71 BP111.33 BP115.51

0

5

10

15

20

25

30

35

CIR

IA 1

04

BS

8002

EC

7-S

TW

EC

7-FR

EW

EC

7-S

AFE

Length (m)BM/50Prop F/50

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Footing BP72.45 BP106.53 BP111.29 BP124-A2.20

Combination 2

Comb1

Combination 1

Combination 2

Combination 2 Comb1

Must check SLS

Serviceability limit state (settlement)

B = 2m ???Apply DA1-2 ULS loadsMULS = 250 kNmApply DA1-1 ULS loadsMULS = 326 kNm

The final design must satisfy all the criteria


Rupture du sol sans instabilité géométrique (grand déplacement)

But what about SLS?

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Serviceability limit states in Section 2



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NA.1 Scope

NA.2 Nationally Determined Parameters

NA.3 Decisions on the status of informative annexes

NA.4 References to non-contradictory complementary information

Bibliography

Annex A (informative)Design Approach and values of partial, correlation and model factors forultimate limit states to be used in conjunction with BS EN 1997-1:2004

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NA.3 Decisions on the status of informative annexes

May be usedChecklist for construction supervision and performance monitoring

J

May be used, noting that relates mainly to buildings

Limiting values of structural deformation and foundation movement

H

May be usedA sample method for deriving presumed bearing resistance for spread foundations on rock

G

May be usedSample methods for settlement evaluationF

May be usedA sample semi-empirical method for bearing resistance estimation

E

May be used, mentioning need for depth factors

A sample analytical method for bearing resistance calculation

D

May be used, with clarification/correction

Sample procedures to determine limit values of earth pressures on vertical walls

C

May be used, but only DA1 relevant to UK

Background information on partial factors for Design Approaches 1, 2 and 3

B

Recommended values adopted except for piling

Partial and correlation factors for ultimate limit states and recommended values

A

Comments in UK National Annex

TitleEC7Annex


NA.4 References to non-contradictory complementary information (NCCI)

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Annex A (informative)Design Approach and values of partial, correlation and model factors forultimate limit states to be used in conjunction with BS EN 1997-1:2007

Values of partial factors recommended in EN1997-1 Annex A

Design approach 1 Combination 1---------------- Combination 2 ----------------Combination 2 - piles & anchorsA1 M1 R1 A2 M2 R1 A2 M1 or … M2 R4

Actions unfav 1,35favunfav 1,5 1,3 1,3

Soil tan φ' 1,25 1,25Effective cohesion 1,25 1,25Undrained strength 1,4 1,4Unconfined strength 1,4 1,4Weight density

Spread Bearing EC7footings Sliding valuesDriven Base 1,7/1.5 1,3piles Shaft (compression) 1.5/1.3 1,3

Total/combined 1.7/1.5 1,3Shaft in tension 2.0/1.7 1.6

Bored Base 2.0/1.7 1,6piles Shaft (compression) 1.6/1.4 1,3

Total/combined 2.0/1.7 1.5Shaft in tension 2.0/1.7 1.6

CFA Base As 1.45piles Shaft (compression) for 1.3

Total/combined bored 1.4Shaft in tension piles 1.6

Anchors Temporary 1,1 1,1Permanent 1,1 1,1

Retaining Bearing capacitywalls Sliding resistance

Earth resistanceSlopes Earth resistance

indicates partial factor = 1.0

C:\BX\BX-C\EC7\[Factors.xls]

Permanent

Variable


A.3 Partial factors for Structural (STR) and Geotechnical (GEO) limit states verification

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NCCI, PDs, Residual Documents and BSs

• CEN requires that conflicting national standards are withdrawn by 2010.

• “Published Documents” – BSI documents with do not have the status of a BS but provide NCCI.

• PD 6694-1, Recommendations for the design of structures subject to traffic loading to BS EN 1997-1

• Out for public comment shortly

• Where does this leave other BS’s?• BS8002, BS8004 – need PDs as Residual Documents• BS8006 – independent• BS8081 – unchanged for the time being• BS6031 – being revised – possible EN to be drafted.