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Eurocodes:
Background & Applications
GEOTECHNICAL DESIGN wi th worked examples 13-14 June 2013, Dublin
Retaining structures I– es gn o grav yw ll
Dr Andrew Bond
Director, Geocentrix Ltd
Chairman TC250/SC7
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Eurocodes:
Background & Applications
w wor e examp es - une, u n
Outline of talk
Scope and contents
Basis of design for gravity walls
Verification of strength
e n orce concre e wa s
Mass gravity walls
Reinforced fill walls
Veri ication o servicea i ity
Supervision, monitoring, and maintenance
Summary of key points
©2005-13 Geocentrix Ltd. All rights reserved2
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Eurocodes:
Background & Applications
GEOTECHNICAL DESIGN wi th worked examples 13-14 June 2013, Dublin
Retaining structures I –
desi n of ravit walls
SCOPE AND CONTENTS
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Eurocodes:
Background & Applications
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Scope of EN 1997-1 Section 9 Retaining
Gravity walls
Walls of stone or lain or reinforced concrete havin a base with orwithout a heel, ledge, or buttress
The weight of the wall itself … plays a significant role in the support ofthe retained material
e.g. concrete gravity walls; spread footing r.c. walls; buttress wallsEmbedded walls – to be covered later
Com osite retainin structures
Walls composed of elements of the above two types
e.g. double sheet pile wall cofferdams; earth structures reinforced by
tendons eotextiles or routin structures with multi le rows ofground anchorages or soil nails
Silos are covered by EN 1991-4
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Eurocodes:
Background & Applications
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Contents of EN 1997-1 Section 9 Retaining
Section 9 applies to retaining structures supporting ground (i.e. soil,rock or backfill) and/or water
§9.1 General (6 paragraphs)
§9.2 Limit states (4)
§9.3 Actions, geometrical data and design situations (26)§9.4 Design and construction considerations (10)
9.5 Determination of earth ressures 23
§9.6 Water pressures (5)
§9.7 Ultimate limit state design (26)
.
Many provisions from Section 6, ‘Spread foundations’ also apply to
©2005-13 Geocentrix Ltd. All rights reserved5
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Eurocodes:
Background & Applications
w wor e examp es - une, u n
Contents of EN 1997-1’s Annexes for retaining
Annex C of Eurocode 7 Part 1 provides informative text relevant toretaining structures
Annex C Sample procedures to determine earth pressures (21
§C.1 Limit values of earth pressure (3 paragraphs)
§C.2 Analytical procedure for obtaining limiting active and passive earth
§C.3 Movements to mobilise earth pressures (4)
©2005-13 Geocentrix Ltd. All rights reserved6
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Eurocodes:
Background & Applications
GEOTECHNICAL DESIGN wi th worked examples 13-14 June 2013, Dublin
Retaining structures I –
desi n of ravit walls
DESIGN SITUATIONS AND LIMIT
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Eurocodes:
Background & Applications
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Limit modes for overall stability and. .
©2005-13 Geocentrix Ltd. All rights reserved8
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Eurocodes:
Background & Applications
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Anticipated and unplanned excavations. . . .
Design geometry shall accountfor anticipated excavation or
Wall type For normal site control
H
possible scour in front of theretaining structure
For ULS verifications:
Cantilever 10% H
Supported 10% height below lowestprop
Maximum 0.5 m
= + Δd nomH H H
©2005-13 Geocentrix Ltd. All rights reserved9
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Eurocodes:
Background & Applications
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Water levels §9.6(3)
When it retains medium or lowpermeability (mainly fine)soils, the wall should bedesigned for a water levelabove formation level
Without reliable drainage, waterlevel should normally betaken at the surface of the
. . w =
With reliable drainage, waterlevel may be assumed to be
. .dw > 0) + maintenancerequirement
©2005-13 Geocentrix Ltd. All rights reserved10
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Eurocodes:
Background & Applications
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Should water pressures be factored?. . .
For ultimate limit states (ULSs)…
design values [of groundwater pressures] shall represent the mostunfavourable values that could occur during the design lifetime of
the structure
For serviceability limit states (SLSs)…design values shall be the most unfavourable values which couldoccur in normal circumstances
[EN 1997-1 §2.4.6.1(6)P]
Design values of ground-water pressures may be derived either byapplying partial factors to characteristic water pressures or by
applying a safety margin to the characteristic water level…
[EN 1997-1 §2.4.6.1(8)]
©2005-13 Geocentrix Ltd. All rights reserved11
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Eurocodes:
Background & Applications
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Possible ways of treating water pressures ,
a es gn wa er eve s or an es gn s ua ons
(b) Characteristic water pressures for SLS design situation
Design pressures for ULS, with... c no ac or app e γ = .
(d) factor on permanent actions (γG = 1.35)
(e) factor on permanent actions (γG = 1.35) applied to normal water level and
©2005-13 Geocentrix Ltd. All rights reserved12
γQ = .
(f) factor on variable actions (γQ = 1.5)
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Eurocodes:
Background & Applications
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Providing a balance between reliability and,
“When partial factors γG
> 1.0 are applied to effective earthpressures, then pore water pressures should also be multiplied by
γG > 1.0 but calculated from highest normal (i.e. serviceability)water levels – i.e. no safety margin is applied (Design Water
Condition 1)
“When partial factors γG = 1.0 are applied [they should be] multipliedb = 1.0 but calculated from hi hest ossible i.e. ultimate
water levels – after an appropriate safety margin has been applied(Design Water Condition 2)”
©2005-13 Geocentrix Ltd. All rights reserved13
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Eurocodes:
Background & Applications
w wor e examp es - une, u n
Recommended treatment of water pressures,
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Eurocodes:
Background & Applications
GEOTECHNICAL DESIGN wi th worked examples 13-14 June 2013, Dublin
Retaining structures I –
desi n of ravit walls
BASIS OF DESIGN FOR GRAVITY
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Eurocodes:
Background & Applications
w wor e examp es - une, u n
Verification of strength for GEO/STR ,
©2005-13 Geocentrix Ltd. All rights reserved16
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Eurocodes:
Background & Applications
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Design Approaches explained
Design Approach
Combination 1 Combination 2
Actions Material Actions/effects Structuralproperties & resistances actions/effects
& materialproperties
A1 + M1 + R1 A2 + M2 + R1 A1 + M1 + R2 A1/A2 + M2 + R3
(Major) factors >> 1.0; (minor) factors > 1.0- =
M1-M2 = factors on material propertiesR1-R3 = factors on resistances
©2013. Author name. All rights reserved17
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Eurocodes:
Background & Applications
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Partial factors for GEO/STR (DA1): footings,,
Parameter Symbol Combination 1 Combination 2
A1 M1 R1 A2 M2 R1
Permanent action (G)Unfavourable γG 1.35
1.0Favourable (γG,fav) 1.0
Unfavourable 1.5 1.3Variable action (Q)
Favourable - (0) (0)
Shearing resistance (tan ϕ) γϕ1.25
’
1.0
c
Undrained shear strength (cu) γcu1.4
Unconfined compressive strength (qu) γqu
γ
Bearing resistance (Rv) γRv
1.0 1.0Sliding resistance (Rh) γRh
©2005-13 Geocentrix Ltd. All rights reserved18
Factors given for persistent and transient design situations
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Eurocodes:
Background & Applications
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Partial factors for GEO/STR (DAs 2/3):, ,
Parameter Symbol Design Approach 2 Design Approach 3
A1 M1 R2 A1# A2* M2 R3
Permanentaction (G)
Unfavourable γG 1.351.35 1.0
Favourable (γG,fav) 1.0
Variable action Unfavourable γQ 1.5 1.5 1.3
Favourable - (0) (0)
Shearing resistance (tan ϕ) γϕ1.25
Effective cohesion (c’) γc
. u γcu
1.4Unconfined comp. str. (qu) γqu
Weight density (γ) γγ 1.0
Bearin resistance R 1.4
1.0Sliding resistance (Rh) γRh 1.1
Earth resistance (Re) wallsγRe
1.4
Earth resistance (Re) slopes 1.1
©2005-13 Geocentrix Ltd. All rights reserved19
Factors given for persistent and transient design situations#
Applied to structural actions; *applied to geotechnical actions
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Eurocodes:
Background & Applications
w wor e examp es - une, u n
National choice of Design Approach for,
©2005-13 Geocentrix Ltd. All rights reserved20
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Eurocodes:
Background & Applications
GEOTECHNICAL DESIGN wi th worked examples 13-14 June 2013, Dublin
Retaining structures I –desi n of ravit walls
VERIFICATION OF STRENGTH:. .
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Eurocodes:
Background & Applications
w wor e examp es - une, u n
Earth pressures on a reinforced concrete wall ,
©2005-13 Geocentrix Ltd. All rights reserved22
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Eurocodes:
Background & Applications
w wor e examp es - une, u n
Active and passive limit states (Annex C)
Eurocode 7 Part 1 (+Corrigendum 1) gives expressions for
active/passive earth pressures:
σ γ ⎛ ⎞
= + − − + +⎜ ⎟∫ 2 (1 / )z
a a aK dz q u c K a c u
σ γ ⎛ ⎞= + − + + +⎜ ⎟∫ 2 (1 / )
z
p p pK dz q u c K a c u
σa(z), σp(z) = active/passive stress normal to wall at depth z
=a p
γ = weight density of retained ground; c = ground cohesion
q = vertical surface load; z = distance down face of wall
©2005-13 Geocentrix Ltd. All rights reserved23
a = wa a es on
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Eurocodes:
Background & Applications
w wor e examp es - une, u n
Rankine’s earth pressure coefficient
Earth pressure coefficient for active conditions, assuming a Rankine
zone forms between the back of the wall and the virtual plane:
β
β β ϕ β
⎛ ⎞− −⎜ ⎟=
2 2
,a
cos cos cosK cos
Ka,β = active earth pressure coefficient for inclined thrust (= σ’ β / σ’ v)
ϕ + −cos cos cos
ϕ = angle of shearing of soil; β = angle of inclination of groundsurface
σ’ = inclined effective stress; σ’ = vertical effective stressWhen β = 0, this reduces to the more familiar:
ϕ −=
1 ina
sK
©2005-13 Geocentrix Ltd. All rights reserved24
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Eurocodes:
Background & Applications
w wor e examp es - une, u n
At rest earth pressures
Earth pressure coefficient for at-rest conditions:
= = ’ ’
0 (1 sin ) (1 sin )K OCRϕ β = − × × +
ϕ = angle of shearing of soil;OCR = overconsolidation ratio (= σ’ v,max / σ’ v)
σ’ h = horizontal effective stress; σ’ v = vertical effective stress
,movement of structure is less than 0.05% of H
Expression is a combination of Meyerhof’s equation for K0 and Kezdi’s
©2005-13 Geocentrix Ltd. All rights reserved25
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Eurocodes:
Background & Applications
GEOTECHNICAL DESIGN wi th worked examples 13-14 June 2013, Dublin
Retaining structures I –desi n of ravit walls
VERIFICATION OF STRENGTH:
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Eurocodes:
Background & Applications
w wor e examp es - une, u n
Earth pressures on a mass gravity wall ,
©2005-13 Geocentrix Ltd. All rights reserved27
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Eurocodes:
Background & Applications
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Charts of Kerisel and Absi’s earth pressure
Charts are not attributed, but
come from Kerisel and Absi’swork. They are the same asappear in BS 8002
Kerisel and Absi assumed lo -
spiral failure surfaces andhence their charts give upperbound values of Ka and K
Charts are given for walls withvertical faces only
, ,a
p
f K
ϕ ϕ ϕ
=⎬ ⎨ ⎬⎪ ⎩ ⎭⎭
©2005-13 Geocentrix Ltd. All rights reserved28
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Eurocodes:
Background & Applications
w wor e examp es - une, u n
‘New’ formulation for active and passive earth
z
a a a acK dz u K q K cγ σ γ ⎛ ⎞
′ = − + −⎜ ⎟ ( )cos cosa
n
K K
γ
β β θ ⎫⎪
= × × −⎬0
z
p p pq pcK dz u K q K cγ σ γ ⎛ ⎞
′ = − + +⎜ ⎟∫
pγ
aK ⎫cosn
pqK
= ×
⎪⎭
β ϕ β
ϕ
− ⎛ ⎞−= −⎜ ⎟±⎝ ⎠
m1 sin
2 cossin
tm ( )1 cot
ac
n pc
K K
ϕ = − ×⎬⎪⎭
2( )tan1 sin sin(2 )
1 sin sin(2 )t wm mw
n
t
mK e
m β θ ϕ ϕ ϕ
ϕ ϕ
± + − −± × ±=
× ±m
δ ϕ δ
ϕ
− ⎛ ⎞= ⎜ ⎟
⎝ ⎠m m
1 sin2 cos
sinwm
©2005-13 Geocentrix Ltd. All rights reserved29
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Eurocodes:
Background & Applications
w wor e examp es - une, u n
Charts of Brinch Hansen’s earth pressure,
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Eurocodes:
Background & Applications
GEOTECHNICAL DESIGN wi th worked examples 13-14 June 2013, Dublin
Retaining structures I –desi n of ravit walls
VERIFICATION OF STRENGTH:
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Eurocodes:
Background & Applications
w wor e examp es - une, u n
No single design method accepted throughout
Eurocode 7 … does not cover the detailed design of reinforced fill
structures. The values of the partial factors … given in EN 1997-1have not been calibrated for reinforced fill structures
[Foreword to EN 14475]
Design of reinforced fill structures is currently carried out to nationalstandards (such as BS 8006)
, , , .delayed the development of a single design method acceptedthroughout Europe
prov es gu ance on e execu on o re n orcestructures
It is hoped that a future European standard will cover design
©2005-13 Geocentrix Ltd. All rights reserved32
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Eurocodes:
Background & Applications
GEOTECHNICAL DESIGN wi th worked examples 13-14 June 2013, Dublin
Retaining structures I –desi n of ravit walls
VERIFICATION OF
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Eurocodes:
Background & Applications
w wor e examp es - une, u n
Verification of serviceability
Verification of serviceability is expressed in Eurocode 7 by:
Ed = design effect of actions (e.g. displacement, distortion)
d d
d . .
For ‘conventional structures founded on clays’, Eurocode 7 allows
calculation for bearing resistance satisfies:
kR
Ek = characteristic effects of actions; Ek = characteristic resistance
γ ,
k
R SLS
©2005-13 Geocentrix Ltd. All rights reserved34
γR,SLS = a partial resistance factor ≥ 3.0
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Eurocodes:
Background & Applications
GEOTECHNICAL DESIGN wi th worked examples 13-14 June 2013, Dublin
Retaining structures I –desi n of ravit walls
SUPERVISION, MONITORING,
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Eurocodes:
Background & Applications
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Supervision of construction (Annex J)
Selected (general) items from checklist in Annex J on supervision of
construction:Verification of ground conditions and of the location and general lay-out
of the structure
Ground-water flow and pore-water pressure regime; effects ofdewatering on ground-water table; effectiveness of measures to
control seepage inflow; corrosion potentialMovements, yielding, stability of excavation walls and base; temporary
suppor sys ems; e ec s on near y u ngs an u es;measurement of soil pressures on retaining structures and of pore-water pressure variations resulting from excavation or loading
©2005-13 Geocentrix Ltd. All rights reserved36
E d
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Eurocodes:
Background & Applications
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Supervision water flow and pore-water
Selected items from checklist in Annex J on water flow and pore-
water pressuresAdequacy of systems to control pore-water pressures in aquifers where
excess pressure could affect stability of base of excavation, includingartesian pressures beneath the excavation; disposal of water fromewater ng systems; epress on o groun -water ta e t roug out
entire excavation to prevent boiling or quick conditions, piping anddisturbance of formation by construction equipment; diversion andremoval of rainfall or other surface water
Control of dewatering to avoid disturbance of adjoining structures orareas; observations of piezometric levels; effectiveness, operation and
maintenance of water recharge systemsSettlement of adjoining structures or areas
Effectiveness of sub-horizontal borehole drains
©2005-13 Geocentrix Ltd. All rights reserved37
Eurocodes:
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Eurocodes:
Background & Applications
w wor e examp es - une, u n
Monitoring and maintenance (Annex J)
Selected items from checklist in Annex J on performance monitoring:
Settlement at established time intervals of buildings and otherstructures including those due to effects of vibrations onmetastable soils
Lateral displacement and distortions, especially those related to fillsand stock iles soil su orted structures such as buildin s or lar etanks; deep trenches
Piezometric levels under buildings or in adjoining areas, especially ifdeep drainage or permanent dewatering systems are installed or if
Deflection or displacement of retaining structures considering: normalbackfill loadings; effects of stockpiles; fills or other surface
loadings; water pressuresFlow measurements from drains
Water tightness
(No specific guidance given for maintenance)
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Eurocodes:
Background & Applications
GEOTECHNICAL DESIGN wi th worked examples 13-14 June 2013, Dublin
Retaining structures I –desi n of ravit walls
SUMMARY OF KEY POINTS
Eurocodes:
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Eurocodes:
Background & Applications
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Summary of key points
Design of gravity walls to Eurocode 7 involves checking that the
ground beneath the wall has sufficient:bearing resistance to withstand inclined, eccentric actions
sliding resistance to withstand horizontal and inclined actions
stabilit to avoid to lin
stiffness to prevent unacceptable settlement or tilt
satisfying the inequalities:
, , p st st
©2005-13 Geocentrix Ltd. All rights reserved40
E d
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Eurocodes:
Background & Applications
GEOTECHNICAL DESIGN wi th worked examples 13-14 June 2013, Dublin
blo .eurocode7.com
www.decodingeurocode2.comwww.decodin eurocode7.com
DECODING THE EUROCODES
E d
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Eurocodes:
Background & Applications
GEOTECHNICAL DESIGN wi th worked examples 13-14 June 2013, Dublin
Geotechnical designw wor ex m l
eurocodes.jrc.ec.europa.eu