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BGA – 10 October 2007 – Geotechnical Eurocodes – preparing for impact1
Geotechnical Eurocodes – preparing for impact
Brian Simpson
Arup Geotechnics
BGA – 10 October 2007 – Geotechnical Eurocodes – preparing for impact2
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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BGA – 10 October 2007 – Geotechnical Eurocodes – preparing for impact3
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.
BGA – 10 October 2007 – Geotechnical Eurocodes – preparing for impact4
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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BGA – 10 October 2007 – Geotechnical Eurocodes – preparing for impact5
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
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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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BGA – 10 October 2007 – Geotechnical Eurocodes – preparing for impact7
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
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• 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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BGA – 10 October 2007 – Geotechnical Eurocodes – preparing for impact9
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”
BGA – 10 October 2007 – Geotechnical Eurocodes – preparing for impact10
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
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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
BGA – 10 October 2007 – Geotechnical Eurocodes – preparing for impact14
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
BGA – 10 October 2007 – Geotechnical Eurocodes – preparing for impact16
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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Serviceability limit states in Section 6
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Serviceability limit states in Section 6
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Serviceability limit states in Section 9
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Serviceability limit states in Section 9
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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
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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
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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.