Introduction to EC7
CE 640/646– Foundation Engineering
Dr. M. C. M. Nasvi
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At the end of this session, you should be
able to:
 Understand the content of EC7
 Differentiate between traditional and EC7 methods
 List Five ULS of EC7
 Define the differences between different design
approaches.
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Outline of the Lecture
o EC7 Background
o Relevant Eurocodes for Geotechnical Design
o Contents of EC7
o Geotechnical Risk
o Design values of Action & Resistance
o EC7 Limit States
o ULS
o SLS
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‘The Eurocodes will become the Europe wide
means
of
designing
Civil
and
Structural
engineering works and so ... they are of vital
importance to both the design and Construction
sectors of the Civil and Building Industries.’
4
1. EC7 Background
 In 1975, Commission of the European Community
decided an action program on the field of construction.
 Aim: to eliminate technical obstacles and harmonize
technical standards among European countries.
5
 Harmonization of the Civil Engineering standards
would
• Provide a common language between the European
Engineers
• Enhance competitiveness of European companies in
world market
• Facilitate the exchange of Engineering services and
products
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For fifteen years, commission, with the help of
steering
committee,
conducted
development
of
Eurocodes programme, which lead to first generation
of European codes in 1980s.
By 2010, all the Eurocodes have been published and
these are now used in all the member states.
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 These set of harmonized technical rules are known as Structural
Eurocodes which comprise of a series of 10 European
Standards, EN 1990 – EN 1999 (EC0 – EC9).
Standards within the Structural Eurocodes programme
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EN1990 Eurocode (EC0)
- Basis of structural design
EN1991 Eurocode 1 (EC1) – Action on structures
EN1992 Eurocode 2 (EC2) – Design of concrete structures
EN1993 Eurocode 3 (EC3) – Design of steel structures
EN1994 Eurocode 4 (EC4) – Design of composite steel and concrete
structures
EN1995 Eurocode 5 (EC5) – Design of timber structures
EN1996 Eurocode 6 (EC6) – Design of masonry structures
EN1997 Eurocode 7 (EC7) – Geotechnical Design
EN1998 Eurocode 8 (EC8) – Design of structures for earthquake
resistance
EN1999 Eurocode 9 (EC9) – Design of aluminium structures
 Eurocode 7 (EN 1997) - concerns geotechnical design.
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2. Relevant Eurocodes for geotechnical design
Standard and
Title
Description
Describes the basis of geotechnical design
and
the
derivation
of
geotechnical
1] BS EN 1997-1: parameters.
2004
Eurocode
7- Geotechnical
Sections
include:
spread
and
pile
Design: Part 1:
foundations,
anchorages,
retaining
General rules
structures, embankments, hydraulic failure
and overall stability.
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Standard and Title
2] BS EN 1997-2:
2007 Eurocode 7Geotechnical
Design:
Part
2:
Geotechnical
investigation
and
testing
3] NA to BS
1997-1: 2004
National Annex
Eurocode
Geotechnical
Design:
Part
General rules
Description
Describes
planning
investigations,
groundwater
soil
&
of
ground
rock
sampling,
measurements,
field
&
laboratory tests in soil and rock, and
requirements of Ground Investigation Report.
EN Each country has its own National Annex
UK for each Eurocode but they may only contain
to
information on those parameters which are left
7open in the Eurocodes for national choice,
1: known
as
Parameters.
Nationally
Determined
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National annex (NA):
 NA is needed as a link between the Eurocode & national
standards of the member states.
 Eurocode states recommended values of partial factors
and actual values may be set by the countries in their NA.
 However, a national annex can change or modify the
content of a Eurocode only where it is indicated that
national choices may be made.
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3. Contents of EC7
EN 1997-1 Geotechnical design Part 1: General rules (CEN, 2004)
•
•
•
•
•
•
•
•
•
•
•
•
Section 1 - General
Section 2 - Basis of geotechnical design
Section 3 - Geotechnical data
Section 4 - Supervision of construction, monitoring and maintenance
Section 5 - Fill, dewatering, ground improvement and reinforcement
Section 6 - Spread foundations
Section 7 - Pile foundations
Section 8 - Anchorages
Section 9 - Retaining structures
Section 10 - Hydraulic failure
Section 11 - Site stability
Section 12 - Embankments
 Informative annexes (A-J) on active & passive earth
pressures, bearing capacity and settlement of foundations
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Contents of EC7 – Part 1
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EN 1997-2 Geotechnical design Part 2: Ground investigation
and testing (CEN, 2007)
• Section 1 - General
• Section 2 - Planning and reporting of ground investigations
• Section 3 - Drilling, sampling and groundwater measurements
• Section 4 - Field tests in soils and rocks
• Section 5 - Laboratory tests on soils and rocks
• Section 6 - Ground investigation report
+Informative annexes
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Contents of EC7 – Part 2
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4. Geotechnical Risk
 A welcome requirement of Eurocode 7 is the mandatory
assessment of risk for all design situations.
... the complexity of each geotechnical design
shall be identified together with the associated
risks ... a distinction shall be made between light
and simple structures and small earthworks ...
with negligible risk [and] other geotechnical
structures. [EN 1997-1 §2.1(8)P]
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When negligible risk is involved, design may
be based on past experience and qualitative
geotechnical investigations.
 In all other cases, quantitative investigations
are required.
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Geotechnical
Category
Description
GC1
Small and relatively simple structures - it is possible to
ensure that fundamental requirements are satisfied on
the basis of experience & qualitative geotechnical
investigations with negligible risk.
GC2
Ex: straightforward ground conditions, local
experience, no excavation below the GWT, etc.
Conventional types of structure and foundation; No
difficult soil or loading conditions; Quantitative
geotechnical data and analysis required;
Routine procedures for field and laboratory testing; No
exceptional risk
Ex: spread, raft and pile foundations, retaining walls,
bridge piers and abutments, embankments, ground
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anchors, tunnels and excavations.
Geotechnical
Description
Category
Those structures not in Categories 1 and 2; Very
large or unusual structures, Difficult ground or
loading conditions; Abnormal risks; Highly seismic
GC3
areas; Areas of ground instability
Ex: Mining, solution, collapsible soils, frost action,
etc.
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 It is not necessary to classify all parts of a project in one
Geotechnical Category.
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 Magnitude & scope of geotechnical investigations must reflect
the structure’s Geotechnical Category.
 Since ground conditions may influence category chosen for the
structure or parts of it, they should be established early on in the
investigation (through a desk study or preliminary field work).
[EN 1997-1 §3.2.1(2)P and 3.2.1(4)]
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5. Design values of action & resistance
 An action - ‘(a) Set of forces (loads) applied to the structure
(direct actions); (b) Set of imposed deformations or
accelerations caused, for example, by temperature changes,
moisture variation, uneven settlement or earthquakes (indirect
actions)’
 A geotechnical action - an ‘action transmitted to the
structure by the ground, fill, standing water or ground-water’
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 A resistance - ‘capacity of a member or component to
withstand actions without mechanical failure’
 An action effect - general term denoting internal forces,
moments, stresses, and strains in structural members - plus
the
deflection
and
rotation
of
the
whole
structure.
[EN 1990 §1.5.3.2]
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A structure subjected to permanent, variable and accidental
actions
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An action and effect of action
 Presence of the load (an action) results in beam deflecting and
internal stresses occurring in its cross-section (effects of the
action).
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Actions
Effect of Actions
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Traditional Approach (BS) vs. EC7
 In contract to traditional lumped factor of safety (FOS)
approach (BS 8004), EC7 promotes the use of Partial
Factor of Safety.
 In the traditional methods, material properties & loads
were treated in an unmodified state and a FOS was
applied at the end of the design process.
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 However, EC7 guides the designer to modify each
parameter early in the design by use of the partial factor
of safety.
 Representative or characteristic values of the parameter
(load, soil strength parameters) is converted to design
value by combining it with the partial factor of safety
for that parameter.
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Design value of action (Fd) or Effect of action (Ed)
𝑫𝒆𝒔𝒊𝒈𝒏 𝒂𝒄𝒕𝒊𝒐𝒏 𝑭𝒅
= 𝑹𝒆𝒑𝒓𝒆𝒔𝒆𝒏𝒕𝒂𝒕𝒊𝒗𝒆 𝒂𝒄𝒕𝒊𝒐𝒏 𝑭𝒓𝒆𝒑 × 𝑷𝒂𝒓𝒕𝒊𝒂𝒍𝒇𝒂𝒄𝒕𝒐𝒓 𝒐𝒇 𝒔𝒂𝒇𝒆𝒕𝒚 (𝜸𝑭 )
𝑫𝒆𝒔𝒊𝒈𝒏 𝒆𝒇𝒇𝒆𝒄𝒕 𝒐𝒇 𝒂𝒄𝒕𝒊𝒐𝒏𝒔
𝒇𝒂𝒄𝒕𝒐𝒓𝒆𝒅 𝒓𝒆𝒑𝒓𝒆𝒔𝒆𝒏𝒕𝒂𝒕𝒊𝒗𝒆 𝒂𝒄𝒕𝒊𝒐𝒏𝒔;
= 𝑬𝒇𝒇𝒆𝒄𝒕 𝒐𝒇
𝒇𝒂𝒄𝒕𝒐𝒓𝒆𝒅 𝒈𝒆𝒐𝒕𝒆𝒄𝒉𝒏𝒊𝒄𝒂𝒍 𝒑𝒂𝒓𝒂𝒎𝒆𝒕𝒆𝒓𝒔; 𝒈𝒆𝒐𝒎𝒆𝒕𝒓𝒊𝒄𝒂𝒍 𝒅𝒂𝒕𝒂
𝑬𝒅 = 𝑬 𝜸𝑭 𝑭𝒓𝒆𝒑 ; 𝑿𝒌 𝜸𝑴 ; 𝒂𝒅
Frep - representative value of an action; 𝒂𝒅 - design value of
geometrical data.
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34
Design value of Geotechnical parameters (Xd)
Design value of geotechnical parameters (Xd) (cohesion,
friction angle, etc.) is derived by dividing the characteristics
values (Xk) by the appropriate partial factor of safety, γM
𝑿𝒌
𝑿𝒅 =
𝜸𝒎
Ex-)
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Example -01]
Determine the design values of the following characteristic
soil strength properties, using the partial factors of safety
provided:
cuk = 40 kPa; ck =5 kPa; φk = 27°.
γcu =1.4; γc' =1.25; γφ' =1.25.
Solution:
𝒄𝒖𝒅 =
𝒄′𝒅
∅′𝒅
𝟒𝟎
𝜸𝒄𝒖
=
𝟒𝟎
𝟏.𝟒
=
𝟓
𝜸 𝒄′
=
𝒕𝒂𝒏 ∅′
−𝟏
𝒕𝒂𝒏
𝜸∅′
=
𝟓
𝟏.𝟐𝟓
= 𝟐𝟖. 𝟓 𝒌𝑷𝒂
= 𝟒 𝒌𝑷𝒂
= 𝒕𝒂𝒏−𝟏
𝒕𝒂𝒏 𝟐𝟕°
𝟏.𝟐𝟓
= 𝟐𝟐. 𝟐°
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Design value of resistance (Rd)
 Resistance (R) is derived from the design values of
actions and ground parameters.
 To determine design resistance (Rd), partial factors may be
applied to ground properties (X) or resistance (R) or to both.
Using ground properties;
Using resistances;
Using both
𝑹𝒅 = 𝑹 𝜸𝑭 𝑭𝒓𝒆𝒑 ; 𝑿𝒌 𝜸𝑴 ; 𝒂𝒅
𝑹𝒅 = 𝑹 𝜸𝑭 𝑭𝒓𝒆𝒑 ; 𝑿𝒌 ; 𝒂𝒅 𝜸𝑹
𝑹𝒅 = 𝑹 𝜸𝑭 𝑭𝒓𝒆𝒑 ; 𝑿𝒌 𝜸𝑴 ; 𝒂𝒅 𝜸𝑹
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Over design factor (߁)
 For ultimate limit state (ULS), effects of the design actions (Ed)
do not exceed the design resistance (Rd) of the structure or
ground (𝑬𝒅 ≤ 𝑹𝒅 ).
 Ratio of resistances to action is termed as over- design factor (𝝉).
𝑶𝒗𝒆𝒓 𝒅𝒆𝒔𝒊𝒈𝒏 𝒇𝒂𝒄𝒕𝒐𝒓 ߁ =
𝑫𝒆𝒔𝒊𝒈𝒏 𝒓𝒆𝒔𝒊𝒕𝒂𝒏𝒄𝒆 (𝑹𝒅 )
𝑫𝒆𝒔𝒊𝒈𝒏 𝒂𝒄𝒕𝒊𝒐𝒏𝒔 (𝑬𝒅 )
𝑭𝒐𝒓 𝒂 𝒔𝒂𝒕𝒊𝒔𝒇𝒂𝒄𝒕𝒐𝒓𝒚 𝒅𝒆𝒔𝒊𝒈𝒏, ߁ ≥ 𝟏
𝑬𝒅
𝑼𝒕𝒊𝒍𝒊𝒛𝒂𝒕𝒊𝒐𝒏 𝑭𝒂𝒄𝒕𝒐𝒓 (𝜦𝑮𝑬𝑶 ) =
≤ 𝟏𝟎𝟎%
𝑹𝒅
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6. EC7 Limit states
 For each geotechnical design situation it shall be verified that no
relevant limit state is exceeded
 Limit states - states beyond which the structure no longer
satisfies the relevant design criteria.
 Section 2 of EN 1997-1 describes basis of geotechnical design &
code states that limit states should be verified by one of four
means:
(1) calculation
(2) prescriptive measures
(3) experimental models and load tests,
(4) an observational method.
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Processes involved in geotechnical design by calculation
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6.1 Ultimate Limit States (ULS)
 EC7 lists five Ultimate limit states to be considered in the
design process:
1. EQU
2. GEO
3. STR
4. UPL
5. HYD
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1. EQU limit state
loss of equilibrium of the structure or the supporting
ground when considered as a rigid body & where internal
strengths of structure & ground do not provide resistance.
This limit state is mostly relevant to structural design.
This limit state is satisfied if sum of design values of effect of
destabilizing actions (Edstb; d) is less than or equal to sum
of design values of effect of stabilizing actions (Estb; d)
𝑬𝒅𝒔𝒕𝒃;𝒅 ≤ 𝑬𝒔𝒕𝒃; 𝒅.
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Verification of EQU limit state
44
2. GEO limit state
 Failure or excessive deformation of the ground, where the soil
or rock is significant in providing resistance.
 This limit state is satisfied if the design actions (Ed) is less than
or equal to the design resistance (Rd), i.e. - 𝑬𝒅 ≤ 𝑹𝒅.
45
3. STR limit state
 STR – failure or excessive deformation of the structure,
where strength of structural material is significant in
providing resistance. As with GEO limit state, STR is
satisfied if the design actions (Ed) is less than or equal to the
design resistance (Rd), i.e. - 𝐸𝑑 ≤ 𝑅𝑑 .
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4. UPL limit state
 loss of equilibrium of the structure or the ground due to uplift
by water pressure (buoyancy) or other vertical actions.
5. HYD limit state
 Hydraulic heave, internal erosion and piping in the ground
caused by hydraulic gradient (i.e. - at the base of a braced
excavation).
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Limit states for earth retaining structures
48
UPL Limit State
HYD Limit State
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Design Approaches (for GEO and STR limit states)
 EC7 permits the adoption of three design approaches:
 Design Approach 1
 Design Approach 2
 Design Approach 3.
 The three design approaches differ in the way in which
they distribute the partial factors.
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Design Approach 1: Combination 1: A1 + M1 + R1
Combination 2: A2 + M2 + R1
Design Approach 2: A1 + M1 + R2
Design Approach 3: A* + M2 + R3
(Note: A*: use set A1 on structural actions and A2 on
geotechnical actions;
A - Actions, M - Material properties and R - Resistance)
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Partial factors set for EQU, GEO and STR limit
states
52
Examples of favorable and unfavourable actions
53
Design Approach 1 (DA 1)
 DA 1 - most likely method to be adopted in most of the
design situations.
 For DA 1, two combinations are available & designer
would
normally
check
the
limit
state
using
each
combination.
Partial factors for design approach 1
The limit state of rupture
All design situations
or excessive deformation
except axially loaded
will not occur with either
piles and anchors
of these combinations
Combination 1
A1 + M1 + R1
Combination 2
A2 + M2 + R1
Design situations
for axially loaded
piles and anchors
A1 + M1 + R1
A2 + (M1 or M2) +
R4
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Partial factors for DA1
Geotechnical Parameter
Partial factors1 on
actions (γF) or
effect of actions
(γE)
Partial factors on
soil parameters
(γM)
Permanent
Symbol
Unfavourable2
Favourable3
Unfavourable
Variable
Favourable
Angle of shearing resistance4
Effective cohesion
Undrained shear strength
Unconfined strength
Weight density
Bearing
Partial resistance
factors (γR) for
Sliding
spread foundations
γG
Combination 1
1.35
A1
γQ
γφ'
γc'
γcu
γqu
γγ
M1
γRv
γRh
Combination 2
1.0
1.5
0
1.0
1.0
1.0
1.0
1.0
1.0
A2
M2
1.0
R1
1.0
1.0
1.3
0
1.25
1.25
1.4
1.4
1.0
1.0
R1
1.0
 Combination 1 - provide safe design against unfavourable deviations
of the actions from their characteristics values.
the ground strength properties from their characteristics values
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 Combination 2 - provide safe design against unfavourable deviations of
DA 1: introduction of partial factors in the checking of ground
bearing capacity: (a) Combination 1 and (b) Combination 2.
A
M
Combination 1
Combination 2
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R
Design Approach 2 (DA 2): A1 + M1 + R2
Design Approach 2 is to check foundation’s reliability by
applying partial factors to actions or action effects and
to resistance simultaneously, while ground strengths are
left unfactored.
 In DA 2 only one verification (A1 + M1 + R2) is ever
required.
57
Design Approach 3 (DA 3): A* + M2 + R3
 Aim is to check the foundation’s reliability by applying
partial factors to structural actions (A1) and to material
properties simultaneously, while geotechnical actions
(A2) and resistance are left mainly unfactored.
 Similar to DA 2, only one verification (A* + M2 + R3) is
required for DA 3.
 In DA 3, the entire calculation is performed with the design
values of the actions and the design shear strength
parameters.
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NOTE:
 An important feature of DA3 is the distinction between
structural and geotechnical actions — larger factors are
applied to the former than to the latter, suggesting greater
uncertainty in their values.
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Example-2]
A concrete foundation is to be cast into a soil deposit as shown
in Figure Ex2 below. The foundation has a representative self
weight, W of 50 kN. During a check for bearing resistance, the
vertical representative actions VG;k and VQ;k are considered as
unfavourable. Determine the design values of each action, for
each Design Approach.
Figure Ex2
60
61
Example-3]
The ground beneath the foundation shown in Figure
Ex-2 above has the following characteristic values:
cuk = 40 kPa; ck = 5 kPa; φk = 25°. Determine the
design values of each property, for each Design
Approach.
62
63
6.2 Serviceability Limit States (SLS)
 For SLS, the effects of the design actions (Ed) do not exceed
the performance criteria (Cd) of the structure.
𝑬𝒅 ≤ 𝑪𝒅.
 Effect of the design actions attempting to exceed the limit
state include deformation, settlement, deflection, ground
heave, vibration, etc.
 Values of partial factors for SLS should normally be
takes as 1.0.
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