ISO 23469:2005

Bases for design of structures - Seismic actions for designing geotechnical works

ISO 23469:2005 provides guidelines for specifying seismic actions for designing geotechnical works, including buried structures (e.g. buried tunnels, box culverts, pipelines, and underground storage facilities), foundations (e.g. shallow and deep foundations, and underground diaphragm walls), retaining walls (e.g. soil retaining and quay walls), pile-supported wharves and piers, earth structures (e.g. earth and rockfill dams and embankments), gravity dams, landfill and waste sites. The guidelines provided in ISO 23469:2005 are general enough to be applicable for both new and existing geotechnical works. However, for use in practice, procedures more specific to existing geotechnical works can be needed, such as those described for existing structures in ISO 13822.

Bases du calcul des constructions - Actions sismiques pour le calcul des ouvrages géotechniques

General Information

• Status: Published
• Publication Date: 10-Nov-2005
• ICS: 91.080.01 - Structures of buildings in general
• ICS: 93.020 - Earthworks. Excavations. Foundation construction. Underground works
• Technical Committee: ISO/TC 98/SC 3 - Loads, forces and other actions
• Drafting Committee: ISO/TC 98/SC 3 - Loads, forces and other actions
• Current Stage: 9092 - International Standard to be revised
• Start Date: 21-May-2025
• Completion Date: 13-Dec-2025

Overview

ISO 23469:2005 - Bases for design of structures: Seismic actions for designing geotechnical works provides practical guidelines for specifying seismic actions when designing geotechnical works. The standard covers soil- and rock-related works such as buried structures (tunnels, culverts, pipelines), foundations (shallow and deep), retaining walls, pile‑supported wharves and piers, earth and rockfill dams and embankments, gravity dams, landfills and waste sites. It is intended for use by experienced practising engineers and code writers and is compatible with ISO 2394.

Key Topics

ISO 23469:2005 structures seismic-design guidance around these core technical topics:

• Seismic hazard analysis (deterministic and probabilistic approaches) for defining reference earthquake motions.
• Site response analysis and assessment of liquefaction potential to evaluate local soil amplification and pore‑pressure effects.
• Spatial variation of ground motion and horizontal wave propagation effects across sites.
• Fault displacements, ground failure and other geotechnical hazards, including liquefaction-induced settlement, lateral spreading and flow failures.
• Methods for specifying seismic actions:
  • Equivalent static analysis (simplified and detailed approaches).
  • Dynamic analysis (simplified and detailed), including inertial and kinematic soil–structure interaction.
• Consideration of paraseismic influences, hydro‑dynamic pressures, and performance criteria (acceptable displacements, strains).
• Informative annexes offering extended guidance (site response, spatial variability, liquefaction assessment, soil‑structure interaction, model‑specific actions).

Applications

This standard is used to:

• Define seismic loading conditions for design and safety assessment of geotechnical works.
• Guide the selection between simplified and advanced analyses depending on performance objectives and consequences of failure.
• Evaluate effects critical to geotechnical performance such as liquefaction, soil‑structure interaction, and fault displacement. Practical applications include design of tunnels, culverts, pipelines, embankments, dams, quay walls, foundations, and landfill stability under seismic loading.

Who should use this standard

• Geotechnical and civil engineers designing or assessing geotechnical works in seismic regions
• Structural engineers dealing with soil–structure interaction
• Code developers and regulators setting seismic design rules
• Consultants performing seismic hazard, site response, and liquefaction analyses

Related Standards

• ISO 2394:1998 - General principles on reliability for structures (compatible)
• ISO 3010:2001 - Seismic actions on structures
• ISO 13822:2001 - Assessment of existing structures (additional procedures for existing geotechnical works)

Keywords: ISO 23469:2005, seismic actions, geotechnical works, liquefaction, site response analysis, seismic hazard analysis, soil‑structure interaction, equivalent static analysis, dynamic analysis.

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 23469
First edition
2005-11-15
Bases for design of structures — Seismic
actions for designing geotechnical works
Bases du calcul des constructions — Actions sismiques pour le calcul
des ouvrages géotechniques
Reference number
©
ISO 2005
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ii © ISO 2005 – All rights reserved

Contents Page
Foreword. iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions. 1
4 Symbols and abbreviated terms . 7
5 Principles and procedure. 7
5.1 Principles. 7
5.2 Procedure for determining seismic actions.9
6 Evaluation of earthquake ground motions, ground failure, and fault displacements. 9
6.1 General. 9
6.2 Seismic hazard analysis . 10
6.3 Site response analysis and assessment of liquefaction potential . 11
6.4 Spatial variation . 12
6.5 Fault displacements, ground failure, and other geotechnical hazards. 14
6.6 Paraseismic influences . 14
7 Procedure for specifying seismic actions . 14
7.1 Types and models of analysis. 14
7.2 Seismic actions for equivalent static analysis . 16
7.3 Seismic actions for dynamic analysis. 17
8 Seismic actions for equivalent static analysis . 17
8.1 Seismic actions for simplified equivalent static analysis . 17
8.2 Seismic actions for detailed equivalent static analysis. 20
9 Seismic actions for dynamic analysis. 21
9.1 Seismic actions for simplified dynamic analysis . 21
9.2 Seismic actions for detailed dynamic analysis . 23
Annex A (informative) Primary issues for specifying seismic actions. 24
Annex B (informative) Upper crustal rock, firm ground, and local soil deposit . 27
Annex C (informative)  Design situations for combination of actions. 29
Annex D (informative)  Seismic hazard analysis and earthquake ground motions . 30
Annex E (informative)  Site response analysis . 36
Annex F (informative)  Spatial variation of earthquake ground motion . 46
Annex G (informative)  Assessment of liquefaction . 51
Annex H (informative)  Seismic actions defined for various models of geotechnical works. 57
Annex I (informative)  Soil-structure interaction for designing deep foundations: phase for inertial
and kinematic interactions . 73
Annex J (informative)  Limitations in the conventional method and emerging trend for evaluating
active earth pressure. 74
Annex K (informative) Effects of liquefaction considered in various models of geotechnical works . 76
Annex L (informative) Evaluation of other induced effects . 80
Annex M (informative) Concepts of response control and protection . 83
Annex N (informative) Interdependence of geotechnical and structure designs. 84
Bibliography . 85
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 23469 was prepared by Technical Committee ISO/TC 98, Bases for design of structures, Subcommittee
SC 3, Loads, forces and other actions in collaboration with ISSMGE/TC4 and CEN/TC205/SC8.
iv © ISO 2005 – All rights reserved

Introduction
This International Standard provides guidelines to be observed by experienced practising engineers and code
writers when specifying seismic actions in the design of geotechnical works. Geotechnical works are those
comprised of soil or rock, including buried structures (e.g. buried tunnels, box culverts, pipelines and
underground storage facilities), foundations (e.g. shallow and deep foundations, and underground diaphragm
walls), retaining walls (e.g. soil retaining and quay walls), pile-supported wharves and piers, earth structures
(e.g. earth and rockfill dams and embankments), gravity dams, landfill and waste sites. The seismic actions
described are compatible with ISO 2394.
The seismic performance of geotechnical works is significantly affected by ground displacement. In particular,
soil-structure interaction and effects of liquefaction play major roles and pose difficult problems for engineers.
This International Standard addresses these issues in a systematic manner within a consistent framework.
The seismic performance criteria for geotechnical works cover a wide range. If the consequences of failure
are minor and the geotechnical works are easily repairable, their failure or collapse may be acceptable and
explicit seismic design may not be required. However, geotechnical works that are an essential part of a
facility handling hazardous materials or a post-earthquake emergency facility shall maintain full operational
capacity during and after an earthquake. This International Standard presents a full range of methods for the
analysis of geotechnical works, ranging from simple to sophisticated, from which experienced practising
engineers can choose the most appropriate one for evaluating the performance of a geotechnical work.

INTERNATIONAL STANDARD ISO 23469:2005(E)

Bases for design of structures — Seismic actions for designing
geotechnical works
1 Scope
This International Standard provides guidelines for specifying seismic actions for designing geotechnical
works, including buried structures (e.g. buried tunnels, box culverts, pipelines and underground storage
facilities), foundations (e.g. shallow and deep foundations, and underground diaphragm walls), retaining walls
(e.g. soil retaining and quay walls), pile-supported wharves and piers, earth structures (e.g. earth and rockfill
dams and embankments), gravity dams, landfill and waste sites.
NOTE The guidelines provided in this International Standard are general enough to be applicable for both new and
existing geotechnical works. However, for use in practice, procedures more specific to existing geotechnical works can be
needed, such as those described for existing structures in ISO 13822.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 2394:1998, General principles on reliability for structures
ISO 3010:2001, Bases for design of structures — Seismic actions on structures
ISO 13822:2001, Bases for design of structures — Assessment of existing structures
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 2394, ISO 3010 and ISO 13822 and
the following apply.
3.1
array observation
simultaneous recording of earthquake ground motions and/or microtremors by an array of seismometers
3.2
basin effects
effects on earthquake ground motions caused by the presence of a basin-like geometrical boundary beneath
the site
NOTE Deep basin effects are defined as effects due to the geometry of the interface between the upper crustal rock
and the overlying firm ground or soil deposits. Shallow basin effects are defined as effects due to the geometry of the
interface between the firm ground (or shallow upper crustal rock) and the local soil deposits and may be treated as part of
the local site response.
3.3
coherency function
function describing a degree of correlation between two time histories
3.4
crest
top of a geotechnical structure, typically defined for embankments and dams
3.5
culvert
tunnel-like structure constructed typically in embankments or ground forming a passage or allowing drainage
under a road or railroad
3.6
damping
mechanism that dissipates energy of motion
3.7
deep foundation
foundation having a large depth to width ratio, which transfers applied loads to deep soil deposits
EXAMPLES Pile foundation, sheet pile foundation, cofferdam foundation, caisson foundation.
3.8
design working life
duration of the period for which a structure or a structural element is designed to perform as intended with
expected maintenance, but without major repair being necessary
3.9
deterministic seismic hazard analysis
seismic hazard analysis based on the selection of individual earthquake scenarios
3.10
dynamic analysis
analysis for computing the dynamic response of a system based on the equations of motion
3.11
earth pressure
pressure from soil on a wall or an embedded portion of a structure
3.12
earth structure
geotechnical work consisting primarily of soil or rock
EXAMPLES Earth and rockfill dams, and embankments.
3.13
earthquake ground motions
transient motions of the ground caused by earthquakes, including those at the ground surface, within the local
soil deposit, and at the interface between the firm ground and the local soil deposit
3.14
effective stress analysis
analysis with consideration of pore pressure changes
3.15
equivalent linear model
linear model incorporating elastic shear moduli and damping factors that are compatible, at various strain
amplitudes, with the non-linear stress-strain relationship under cyclic loading
2 © ISO 2005 – All rights reserved

3.16
equivalent static analysis
static analysis that approximates the dynamic response of the system
3.17
excess pore water pressure
change of water pressure in the soil pores with respect to those at a reference state
3.18
failure mode
pattern of failure defined by distinctive features of the deformed shape after failure
3.19
fault displacement
permanent tectonic ground displacement associated with fault dislocation
3.20
firm ground
soft rock or stiff soil layer
3.21
free field
ground not subject to the effect of geotechnical works or structures
3.22
geotechnical characterization
specification of material and geometrical parameters of soil or rock
3.23
geotechnical hazard
hazard associated with geotechnical phenomena, including ground failure and subsidence
3.24
geotechnical work
work that includes soil or rock as primary components with or without structural parts made of concrete, steel,
or other materials
EXAMPLES Buried structures (e.g. buried tunnels, box culverts, pipelines and underground storage facilities),
foundations (e.g. shallow and deep foundations, and underground diaphragm walls), retaining walls (e.g. soil retaining and
quay walls), pile-supported wharves and piers, earth structures (e.g. earth and rockfill dams and embankments) gravity
dams, landfill and waste sites.
3.25
ground failure
mass movement of soil including liquefaction-induced ground deformations (settlement, lateral spreading, flow
failure) and non-liquefaction-induced ground deformations (seismic compaction, permanent deformations and
landslides)
3.26
horizontal wave propagation effect
effect causing spatial variation of ground motion in the horizontal direction due to the finite speed of wave
propagation
3.27
hydro-dynamic pressure
transient pressure exerted by a fluid on a structure in a system subject to dynamic motion
3.28
importance of a structure or facility
degree of possible consequences of failure of a structure or facility caused by a reference earthquake motion
3.29
inertial interaction
part of soil-structure interaction arising from the inertia forces acting on the structure
3.30
kinematic interaction
part of soil-structure interaction arising from the deformation of the soil relative to that of the structure
3.31
liquefaction
large drop in soil shear strength and/or stiffness caused by an increase in pore water pressure that may cause
significant reduction in the shear resistance of geotechnical works and ground or may induce large ground
displacement
3.32
liquefaction potential
susceptibility of the soil to the onset of liquefaction under a reference earthquake motion
3.33
local site effect
effect of the local geological configuration on earthquake ground motions
3.34
lumped mass
mass assigned at discrete points of a model representing a continuum
3.35
microtremors
small amplitude vibration of the ground generated by either human activities or natural phenomena
3.36
overstrength
strength of a structure or structural element, typically specified by the ratio of actual strength to nominal design
strength
3.37
performance criteria
set of conditions for specifying the response of a geotechnical work to meet the expected state defined by
engineering parameters, such as acceptable displacements, strains or stresses, that characterize the
performance objectives of design
3.38
performance objective
expression of the expected performance of a facility in order to fulfil its purposes and functions
3.39
phase velocity
velocity at which a monochromatic seismic wave travels along a surface
3.40
pipeline
long tube or a network of tubing used for the transportation of fluid, gas, or solid mixed with fluid or gas
3.41
probabilistic seismic hazard analysis
seismic hazard analysis considering the probability of occurrence of different levels of ground shaking at a site
during the reference period
4 © ISO 2005 – All rights reserved

3.42
reference earthquake motions
earthquake motions specified for evaluating seismic performance of a geotechnical work (seismic actions are
specified, in a subsequent stage, based on the reference earthquake motions)
3.43
residual displacement
displacement present after the earthquake, typically due to non-reversible deformation or sliding
3.44
residual response
response of a system remaining after the earthquake
3.45
residual strength
shear strength of the soil after failure including liquefaction
3.46
retaining wall
wall supporting backfill soil, embankment soil or a cut slope
3.47
scenario earthquake
earthquake that is specified for determining earthquake ground motions typically by deterministic seismic
hazard analysis
3.48
seismic actions
loads, deformations, or other actions imposed upon models of structures and geotechnical works during and
after an earthquake
3.49
seismic coefficient
coefficient that represents the dynamic forces on the structure by static forces as a fraction of the weight of the
structure
3.50
seismic coefficient approach
static approach in which the dynamic response of soil-structure system is evaluated by an inertia force
distributed over the system
3.51
seismic hazard analysis
analysis for determining earthquake ground motions on the basis of the regional seismic activity and
characteristics of source and wave propagation
3.52
seismic performance
response of a structure or geotechnical work during and after an earthquake compared to specified
performance criteria
3.53
shallow foundation
foundation having a small depth to width ratio, which is supported directly by soil at or near the ground surface
without using piles or other structural elements
EXAMPLES Spread foundation, footing foundation.
3.54
site amplification factor
factor describing the increase in amplitude of earthquake motions in local soil deposit, defined as the ratio of
the peak ground surface motion to the peak earthquake motion input to the local soil deposit
3.55
site classification
differentiation of sites based on soil profile and other parameters
3.56
site response analysis
analysis of the response of a site to earthquake ground motion taking into account the local soil deposits
3.57
site-specific
characterization of conditions specific to a site
3.58
sliding soil mass
portion of a geotechnical work, typically defined as that part of the soil or rock expected to slide along a failure
surface
3.59
soil-structure interaction
effect by which soil and adjacent structures mutually affect their overall response
3.60
spatial variation of ground motion
lateral variations of ground motion over a given area
3.61
stress resultants
bending moments, shear forces and axial forces in a structure
3.62
subgrade reaction
resulting stresses on a surface in the ground (typically a surface of a foundation or retaining wall) due to
external loading
3.63
superstructure
that part of a structure constructed above the ground surface
NOTE This definition is adopted for the purpose of this International Standard (for further discussion, see H.2).
3.64
surface wave
seismic wave that travels along the ground surface and whose amplitude decreases exponentially in the half
space with depth
3.65
threshold limit
limit beyond which a structure exhibits an irreversible response
EXAMPLES Sliding limit, elastic limit.
6 © ISO 2005 – All rights reserved

3.66
total stress analysis
analysis without explicit consideration of pore pressure changes
EXAMPLES Linear analysis, equivalent linear analysis, non-linear total stress analysis.
4 Symbols and abbreviated terms
CPT cone penetration test
FE finite element
LDPT large diameter penetration test; detailed specifications are available for Becker penetration test
PSHA probabilistic seismic hazard analysis
SPT standard penetration test
1-D one-dimensional
2-D two-dimensional
3-D three-dimensional
5 Principles and procedure
5.1 Principles
5.1.1 Purposes and functions
In designing geotechnical works, the purposes and functions shall be defined in accordance with broad
categories of use such as commercial, public and emergency use.
5.1.2 Performance objectives for seismic design
Performance objectives for seismic design of geotechnical works should generally be specified on the
following basis, depending on the expected functions during and after an earthquake:
⎯ serviceability during and after an earthquake: minor impact to social and industrial activities, the
geotechnical works may experience acceptable residual displacement, with function unimpaired and
operations maintained or economically recoverable after temporary disruption;
⎯ safety during and after an earthquake: human casualties and damage to property shall be minimized,
geotechnical works that are an essential part of a facility handling hazardous materials or
a post-earthquake emergency facility shall maintain full operational capacity, and geotechnical works
shall not collapse.
The performance objectives should also reflect the possible consequences of failure.
Seismic actions on geotechnical works shall be specified, which are compatible with the performance
objectives.
NOTE The collapse of a certain type of geotechnical works such as pipelines might not necessarily cause human
casualties if fail-safe measures such as shutdown valves are provided. In this design situation, the collapse can be
allowed.
5.1.3 Reference earthquake motions
For each performance objective described in 5.1.2, reference earthquake motions shall be specified for
evaluating seismic performance of the geotechnical works as follows:
⎯ for serviceability during or after an earthquake: earthquake ground motions that have a reasonable
probability of occurrence during the design working life;
⎯ for safety during or after an earthquake: earthquake ground motions associated with rare events that may
involve very strong ground shaking at the site.
NOTE Annex D describes in more detail the concepts of reference earthquake motions and their applicability in
different circumstances.
5.1.4 Performance criteria and limit states
Performance criteria shall generally be specified by engineering parameters that characterize the response of
geotechnical works to the reference earthquake motions. These engineering parameters shall be specified
considering the design working life.
The engineering parameters depend on the process for verifying that the performance criteria have been met.
The importance of the facility differentiates the level of performance objectives. These issues shall be taken
into account in the formulation of the performance criteria.
The seismic performance of geotechnical works can be described with reference to a specified set of limit
states. These limit states are
⎯ serviceability limit state during or after an earthquake: a limit state for satisfying serviceability during and
after an earthquake, and defined by an acceptable state of displacement, deformation, or stress, and
⎯ ultimate limit state during or after an earthquake: a limit state for satisfying safety requirements during and
after an earthquake, and defined by a state with appropriate margin against collapse.
More than one serviceability limit state may be introduced. For example, if one serviceability limit state is
defined as the state with no residual displacements, another serviceability limit state may be defined as the
state with an acceptable residual displacement and operation of the facility recoverable after minimum
disruption with reasonable cost for repair.
One may evaluate only one limit state, provided that the seismic performance objectives specified by other
limit states can be satisfied through the evaluation of the one limit state.
NOTE 1 In conventional seismic design of geotechnical works based on the equivalent static method, a seismic
coefficient has been used to achieve both serviceability and safety during and after an earthquake. However, as a result of
case histories of seismic damage during the 1990s, limitations of conventional seismic design have been recognized
widely. The approach described in this International Standard can be used to overcome these limitations.
NOTE 2 The conventional approach in which margin to a specified limit state is specified in terms of the load factor is
described in ISO 3010.
5.1.5 Specific issues related to geotechnical works
Seismic actions on geotechnical works shall be specified taking the following factors into account:
⎯ seismic response that involves non-linear behaviour of soil and structural materials;
⎯ appropriate mode of and path to failure so that damage can be readily repaired and local failure of a
geotechnical work does not immediately lead to global failure;
⎯ performance criteria in terms of residual displacements, deformations, strains and stability;
8 © ISO 2005 – All rights reserved

⎯ soil-structure interaction, including fluid-structure interaction, that is often simplified as actions on a local
system within a global system.
These factors can be sensitive to the details of earthquake ground motions. Improved knowledge shall be
used through the procedures described in Clause 6 for evaluating earthquake ground motions in designing
geotechnical works.
5.2 Procedure for determining seismic actions
Seismic actions on geotechnical works shall be determined as follows:
1st stage: characterize
⎯ the firm ground (or bedrock) motion at the site through seismic hazard analysis;
⎯ the fault displacements if applicable;
⎯ the free field earthquake motions by site response analysis; and
⎯ the potential for earthquake-induced phenomena such as ground failure and other geotechnical hazards,
including liquefaction;
2nd stage: specify, based on the results of the 1st stage, the seismic actions due to
⎯ the earthquake ground motions;
⎯ the ground displacements due to fault movement; and
⎯ ground failure and other geotechnical hazards, taking due account of the methods of analysis to be used
for modelling the geotechnical works.
Clauses 7 to 9 describe seismic actions on various models of analysis.
NOTE Annex A presents the primary issues for specifying seismic actions. Seismic actions depend on the model of
analysis.
6 Evaluation of earthquake ground motions, ground failure, and fault
displacements
6.1 General
6.1.1 Earthquake ground motions and fault displacements
In the 1st stage described in 5.2, earthquake ground motions defined in 5.1.3 and fault displacements shall be
evaluated for use as basic variables in subsequent analyses (i.e. in the 2nd stage described in 5.2) for
specifying seismic actions on geotechnical works.
6.1.2 Ground failure and other geotechnical hazards
Liquefaction potential shall also be evaluated in the 1st stage described in 5.2 (see Annex G). If liquefaction is
judged to occur, the effects of liquefaction shall be incorporated in the 2nd stage described in 5.2 either as
seismic actions or effects on the model of the soil-structure system, depending on the models and methods of
analysis used. Ground displacements due to liquefaction, including induced ground displacement, shall be
evaluated in the 1st stage described in 5.2 as basic variables to be used in the subsequent analysis for
specifying seismic actions.
The potential for ground failure in the form of landslides or deformations shall be evaluated.
The potential for flooding or inundation due to subsidence or ground failure may be considered.
6.2 Seismic hazard analysis
6.2.1 Probabilistic and deterministic analyses
The earthquake ground motions, liquefaction potential, ground failure, and fault displacements shall be
determined by either probabilistic or deterministic analyses.
The earthquake ground motion for evaluating serviceability during or after an earthquake shall be determined
by probabilistic analysis.
The earthquake ground motion for evaluating safety during or after an earthquake shall be determined by
either probabilistic or deterministic analysis. This earthquake ground motion can be determined by
deterministic analysis when an active seismic fault is assumed to be located nearby. As in ISO 3010, the
earthquake ground motion for evaluating safety during or after an earthquake in a region of low seismicity may
be determined by deterministic analysis (see Annexes C and D).
NOTE 1 A deterministic analysis evaluates earthquake ground motion by selecting individual earthquake scenarios,
including earthquake magnitude, fault location, fault dimension, and source mechanism. Deterministic analysis does not
explicitly consider the probability of occurrence of earthquakes, but it does consider uncertainties involved in the
evaluation of ground motion from a scenario earthquake. An approximate range of probability of occurrence of the
earthquake ground motion from the scenario earthquake can be assessed taking into account the regional seismic activity.
NOTE 2 At the current state of practice, earthquake ground motions are often determined on an empirical or historical
basis.
NOTE 3 An active seismic fault is a fault that is capable of generating earthquakes and has moved during the recent
geological period. There are wide variations in the time periods since the last fault movement that are used to define an
active seismic fault.
6.2.2 Analysis for evaluation of earthquake ground motion
Both probabilistic and deterministic seismic hazard analyses should capture the characteristics of the ground
motions based on earthquake magnitude, fault type and distance with or without site parameters. More
detailed seismic hazard analyses should capture the near source effects and directivity effects and should be
based on seismic source parameters (e.g. the geometry of the active fault and propagation of fault rupture),
attenuation of earthquake motions from the fault, and deep basin effects. The uncertainties in the model
parameters of the seismic source, attenuation relations, and deep basin effects should be considered (see
Annex D).
Seismic hazard analysis methods including empirical, semi-empirical, and theoretical methods, or a
combination of these methods, shall be chosen, consistent with the degree of refinement required for analysis
of the geotechnical works, based on
⎯ the importance of a structure, and
⎯ the available information on seismic faults and deep basin structures in the vicinity of a site.
Results of seismic hazard analysis may be available over a country or region from the relevant authorities
giving the representative values of earthquake ground motions for use in the subsequent analyses.
6.2.3 Outputs of seismic hazard analysis
Earthquake ground motions at the interface between firm ground and local soil deposits shall be developed
through seismic hazard analysis for use in design of geotechnical works.
10 © ISO 2005 – All rights reserved

The earthquake ground motions can be specified in terms of simple scalar values (e.g. peak acceleration,
peak velocity, peak displacement, Fourier and response spectral values) or time histories of acceleration,
velocity, and displacement. The earthquake ground motions can include spatial variation. An appropriate set
of variables shall be evaluated for specifying the seismic actions depending on the models and the methods of
analysis.
The ground motions at the interface between the firm ground and local soil deposit can be used in a
subsequent analysis for site response analysis, assessment of liquefaction potential and for dynamic analysis
of soil-structure systems.
NOTE Even if the earthquake ground motions at the ground surface are not directly used for seismic design of the
geotechnical works, it is advisable to compute these motions in order to confirm the consistency of the seismic design with
the design of buildings and other structures constructed above the ground surface.
6.3 Site response analysis and assessment of liquefaction potential
6.3.1 General
The earthquake motions at the ground surface and within the subsoil shall be obtained for use in determining
seismic actions on geotechnical works. The assessment of liquefaction potential shall also be performed for
evaluating the effects on performance of geotechnical works.
To this end, the methods may be broadly categorized as follows (see Figure E.7):
a) empirical analysis: based on a site category using prescribed site amplification factors;
b) site-specific simplified analysis: based on the assumed response mode on a site-specific basis
[one-dimensional (1-D) lumped mass model];
c) site-specific simplified dynamic analysis: based on total or effective stress analysis on a site-specific basis,
typically by 1-D analysis;
d) site-specific detailed dynamic analysis: based on coupled soil-structure interaction analysis of
geotechnical works on a site-specific basis. For foundations, 2-D or 3-D analysis should be performed.
From the methods a) through c), the computed earthquake motion variables at the ground surface, ground
displacement in the subsoil, and liquefaction potential, can be used as input for subsequent simplified analysis
of geotechnical works, as described in Clauses 8 and 9. The method d) directly computes the seismic
response of geotechnical works.
The methods used for site response analysis and assessment of liquefaction potential shall be selected on the
basis of
⎯ required seismic behaviour specified by performance criteria, and
⎯ quality of geotechnical data from the site.
Effects of topography and irregular stratigraphy should be considered where applicable.
6.3.2 Empirical analysis
In empirical analysis, local site effects may be evaluated using prescribed site amplification factors that are
based on statistical analysis of field data and associated with specific site categories. In-situ site parameters
such as shear wave velocity, standard penetration test (SPT) N-value, and cone penetration test (CPT) data
over a specified or total depth and the thickness of the local soil deposits above the firm ground can be used
to establish the site classification. Geological data can also be used to establish the site classification. This
site classification leads to the use of specified site amplification factors or site dependent response spectra.
Geotechnical characterization through microtremor measurements and any available earthquake motion
records obtained nearby would improve the reliability of the evaluation of local site effects.
From the results of the site response analysis, liquefaction potential can be evaluated based on appropriate
in-situ geotechnical tests, including SPT and CPT for sandy or non-plastic silty soil, or large diameter
penetration tests (LDPT) for gravelly soil, using generally accepted empirical correlations.
6.3.3 Site-specific simplified analysis
In the simplified analysis of site response, local site effects may be evaluated with the aid of modal analysis on
a site-specific basis. This type of analysis can determine maximum site responses, including peak ground
displacements, at specified depths in the ground.
From the results of the site response analysis, the liquefaction potential of sandy or non-plastic silty soils can
be evaluated using generally accepted liquefaction assessment charts based on results of in-situ geotechnical
tests, including SPT, CPT, LDPT or shear wave velocity measurement.
6.3.4 Site-specific simplified dynamic analysis
Dynamic site response may be evaluated numerically either through total stress analysis of the free field using
equivalent linear or non-linear models or through effective stress analysis. This analysis is typically done by
1-D analysis. The site response can be represented by time histories of acceleration, shear stress, and
shear strain at specified locations in the ground.
Shear stress ratios derived from time histories from a total stress analysis are used for evaluating liquefaction
potential based on a comparison with the cyclic resistance evaluated by cyclic laboratory tests, and/or from
empirical procedures based on appropriate in-situ geotechnical test data, including SPT, CPT, LDPT data, or
shear wave velocity.
If a geotechnical work is designed for a site susceptible to liquefaction, effective stress analysis of the free
field response may be carried out to determine the relevant site response parameters. Total stress analysis
may also be used by incorporating the effects of liquefaction through appropriate reduction of shear moduli.
6.3.5 Site-specific detailed dynamic analysis
In detailed dynamic analysis of a soil-structure system, site response is often not evaluated independently but
can be evaluated as a part of the soil-structure interaction analysis of geotechnical works on a site-specific
basis. The analysis can be done through appropriate numerical procedures such as finite element, finite
difference, or boundary element methods. The analysis can be carried out on 2-D or 3-D models of the soil
profile (see 9.2).
6.4 Spatial variation
6.4.1 General
The spatial variation of earthquake ground motions shall be evaluated for the design of a long or a large
structure when the lateral dimension of the structure is large enough compared with the representative
seismic wavelength. Annex F describes this issue in more detail.
Earthquake ground motions can vary spatially due to signifizant variation in topography, soil properties, and
stratigraphy in the lateral direction. Appropriate characterization for lateral variation in these geotechnical
conditions shall be performed. The characterization effort can involve additional field tests, evaluation of
uncertainty through different models of the site profile, or a combination of both.
When the lateral variation in the geotechnical conditions is negligible, the horizontal wave propagation effect
can be the major cause of the spatial variation. Among the seismic waves that cause the horizontal wave
propagation effect are surface waves and inclined shear waves. Parameters such as phase velocity,
wavelength and direction of propagation shall be appropriately defined for evaluating spatial variation. In
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addition to the horizontal wave propagation effect, spatial incoherency, which can be predominant at high
frequencies, may be defined using a coherency function.
Analysis of spatial variation may be broadly categorized as follows:
a) empirical analysis: based on an assumed distribution of harmonic static ground displacement in the
horizontal direction, or based on the coherency function. Such analysis can be combined with the site
response analysis described in 6.3.2 or 6.3.3;
b) site-specific simplified analysis: based on the surface wave propagation effect, which is evaluated on a
site-specific basis. Such analysis may be combined with the site response analysis described in 6.3.4;
c) site-specific simplified dynamic analysis: based on the site response analysis (6.3.4) performed at
multiple locations;
d) site-specific detailed dynamic analysis: based on the evaluation of the effects of lateral variation in
geotechnical conditions.
The analysis described in a) and b) evaluates the spatial variation due to horizontal wave propagation effect
and/or spatial incoherency and is applied where the lateral variation in the geotechnical conditions is not
significant. The analysis described in c) and d) evaluates the spatial variation due to lateral variation in
geotechnical conditions.
Spatial variations in soil conditions or properties can affect the local displacements of a geotechnical work
even if the earthquake ground motions are not considered to vary spatially across the structure. Allowance
shall be made for variations in local displacements based on knowledge of the site heterogeneity, the
characteristics of the structure, and the simplifications of the site conditions made for analysis (see Annex L).
6.4.2 Empirical analysis
In empirical analysis, spatial variation of earthquake ground motions may be evaluated based on an assumed
distribution of harmonic static ground displacement in the horizontal direction at the depth of a buried structure
or
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