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Issue record Issue Date Comments 1 August 2003 New standard 2
August 2004 Amended to agree with RT/CE/S/020, RT/CE/P/044,
RT/CE/S/066, RT/CE/S/067 and RT/CE/S/141. 3 March 2010 Complete
revision to accommodate the use of the suite of
Structural Eurocodes 4 June 2011 Revision to 10.3.2 and 10.3.3
to correct the values of the
partial factors; to 11.6, 11.7 and 11.9 (new) to clarify the
design requirements for unplanned excavations and passive
pressures; and 12.3 to emphasise the requirements for producing a
Ground Investigation Report. Editorial changes, to remove
inconsistencies and improve the clarity of the text.
Compliance This Network Rail standard is mandatory and shall be
complied with by Network Rail and its contractors if applicable
from 3rd September 2011. When this standard is implemented, it is
permissible for all projects that have formally completed GRIP
Stage 3 (Option Selection) to continue to comply with the issue of
any relevant Network Rail standards current when GRIP Stage 3 was
completed and not to comply with requirements contained herein,
unless stipulated otherwise in the scope of this standard.
Reference documentation The Railways (Interoperability)
Regulations 2006 (Statutory Instrument 2006 No. 397) Health and
Safety at Work Act 1974 Construction (Design and Management)
Regulations 2007 Building Regulations BS 1377 [various parts]
Methods of test for soils for civil engineering purposes
[various sub-titles]
BS 5930 Code of practice for site investigations BS 8006 Code of
Practice for strengthened/reinforced soils and other
fills BS 10175 Code of Practice on investigation of potentially
contaminated
sites BS EN 1990 Basis of structural design NA BS EN 1990 UK
National Annex to Eurocode. Basis of structural design
(2002) + A1 (2005) BS EN 1991 [various parts]
Actions on structures [various sub-titles]
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BS EN 1991-2 Actions on structures. Part 2: Traffic loads on
bridges BS EN 1997-1 Geotechnical design: General rules BS EN
1997-2 Geotechnical design: Ground investigations and testing BS EN
ISO 14688-1 Geotechnical investigation and testing. Identification
and
classification of soil. Identification and description BS EN ISO
14688-2 Geotechnical investigation and testing. Identification
and
classification of soil. Principles for a classification BS EN
ISO 14689-1 Geotechnical investigation and testing. Identification
and
classification of rock. Identification and description BS ISO
5667-11, BS 6068.11
Water quality. Sampling. Guidance on sampling of
groundwaters
GC/RT5212 Requirements for defining and maintaining clearances
NR/GN/CIV/801 The application of the Observational Approach to the
design
of remedial works to Earthworks NR/L1/AMG/1010 Policy on working
safely in the vicinity of buried services NR/L1/TRK/05200
Vegetation NR/L2/AMG/1020 Buried services data provision
NR/L2/AMG/1030 Working safely in the vicinity of buried services
NR/L2/AMG/1040 Buried services data feedback NR/L2/CIV/003
Engineering Assurance of Building and Civil Engineering
Works NR/L2/INI/CP0047 Application of the Construction Design
and Management
Regulations to Network Rail construction projects NR/L3/CIV/005
Railway drainage manual NR/L3/CIV/037 Managing the risk arising
from mineral extraction and landfill
operations NR/L3/CIV/038 Managing the potential effects of coal
mining subsidence NR/L3/CIV/140 Model Clauses for Civil Engineering
works NR/L3/CIV/151 Technical Approval of Standard Details and
Designs for Civil
Engineering Works NR/SP/OHS/069 Lineside facilities for personal
safety Highways Agency Design Manual for Roads and Bridges CIRIA
Report C580 Embedded retaining walls - guidance for economic design
The Federation of Piling Specialists
ICE Specification for piling and embedded retaining walls (2nd
Edition: 2007)
D C Wyllie and C Mahe
Rock Slope Engineering (published by Taylor and Francis)
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Disclaimer In issuing this document for its stated purpose,
Network Rail makes no warranties, express or implied, that
compliance with all or any documents it issues is sufficient on its
own to ensure safe systems of work or operation. Users are reminded
of their own duties under health and safety legislation.
Supply Copies of documents are available electronically, within
Network Rail’s organisation. Hard copies of this document may be
available to Network Rail people on request to the relevant
controlled publication distributor. Other organisations may obtain
copies of this document from IHS. Tel: 01344 328039.
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Contents 1 6 Purpose2 6 Scope3 6 Roles and responsibilities4 6
Definitions5 8 Governing requirements6 11 Design objectives and
situations7 13 Design approach8 17 Design Categories9 17 Design,
construction and specification of geotechnical projects10 22 Design
requirements11 26 Particular requirements for various types of
structures12 35 Geotechnical investigations
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1 Purpose
The purpose of this standard is to define the requirements for
geotechnical designs undertaken for Network Rail.
2 Scope
This standard is applicable to all types of ‘structure’, which
is defined in BS EN 1990: Basis of structural design as an
‘organised combination of connected parts, including fill placed
during execution of the construction works, designed to carry loads
and provide adequate rigidity’. Thus this standard is applicable to
the geotechnical design of all types of building and civil
engineering works - such as Earthworks; retaining walls; the
foundations, piers, abutments and wing walls of bridges; and
foundations to buildings.
This standard does not apply to Track support systems.
3 Roles and responsibilities
Roles, responsibilities and competencies of those involved in
the production and checking of geotechnical designs shall be in
accordance with NR/L2/CIV/003: Engineering Assurance of Building
and Civil Engineering Works.
4 Definitions
characteristic value (of a geotechnical parameter) A cautious
estimate of the value (of a geotechnical parameter) affecting the
occurrence of the limit state, which takes account of the volume
and quality of the test results, the variability of the ground, and
the type of structure.
comparable experience Documented or clearly established
information related to the ground being considered in design,
involving the same types of soil and rock for which similar
geotechnical behaviour is expected, and involving similar
structures. Information gained locally is particularly
relevant.
construction works Everything that is constructed or results
from construction operations.
design criteria Quantitative formulations that describe for each
limit state the conditions to be fulfilled.
design situations Sets of physical conditions representing the
real conditions occurring during a certain time interval for which
design will demonstrate that relevant limit states are not
exceeded.
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design value The value of a variable used in the calculation of
the dimensions, forces on or in the structure being designed. The
design value for a geotechnical parameter (such as the strength of
a soil) can (a) be derived by dividing the characteristic strength
of the soil by the appropriate partial factor, or (b) be assessed
directly.
design working life Assumed period for which a structure or part
of it is to be used for its intended purpose with anticipated
maintenance but without major repair being necessary.
Earthwork An Embankment, Cutting (soil or rock) or Natural Slope
(soil or rock), or nailed or reinforced soil structure whose face
angle is less than 70 degrees to the horizontal.
execution All activities carried out for the physical completion
of the work including procurement, the inspection and documentation
thereof.
geotechnical action Action transmitted to the structure by the
ground, fill, standing water or ground water.
ground Soil, rock and fill in place prior to the execution of
the construction works.
Geotechnical Design Report A presentation of assumptions, data,
calculations and results of the verification of safety and
serviceability of a geotechnical design. A Geotechnical Design
Report will also contain a Ground Investigation Report and a plan
for any monitoring work.
Ground Investigation Report A presentation of all available
geotechnical information (including geological features and
relevant data) and a geotechnical evaluation of that information
(including the assumptions made in interpreting the results of
tests).
limit states States beyond which the structure no longer fulfils
the relevant design criteria.
serviceability limit states States that correspond to conditions
beyond which specified service requirements for a structure or
structural member are no longer met. ultimate limit states States
associated with collapse or with other similar forms of structural
failure.
load case Compatible load arrangements, sets of deformations and
imperfections considered simultaneously with fixed variable actions
and permanent actions for a particular verification.
method of construction Manner in which the execution will be
carried out.
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resistance Capacity of a member or component, or cross-section
of a member or component of a structure to withstand actions
without mechanical failure.
stiffness Material resistance against deformation.
strength Mechanical property of a material indicating its
ability to resist actions, usually given in units of stress.
Structural Assessment The determination or confirmation of the
stability or safe-load bearing capacity of a structure.
structural system Load-bearing members of a building or civil
engineering works and the way in which the members function
together.
structure Organised combination of connected parts, including
fill placed during execution of the construction works, designed to
carry loads and provide adequate rigidity.
Temporary works Any works in place for less than twelve
months.
Track support system The structure that provides immediate
support to the track; it includes the formation, capping layers,
blanketing, ballast, geosynthetics that are integral with the
support system, and Longitudinal Timbers.
5 Governing requirements
5.1 Regulations, legislation and standards
Design and construction works shall comply with the requirements
of the following.
1. The Railways (Interoperability) Regulations 2006.
2. Relevant legislation, such as the Health and Safety at Work
Act 1974, and the Construction (Design and Management) Regulations
2007.
3. Building Regulations (for example, regarding the minimum
depth of a foundation).
4. Railway Group Standards (for example, GC/RT5212: Requirements
for defining and maintaining clearances).
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5. Network Rail standards (for example, NR/L2/CIV/003, and
NR/L2/INI/CP0047: Application of the Construction Design and
Management Regulations to Network Rail construction projects).
6. Standards governing design, methods of construction, product
specifications etc: details of which are given in 9.
Any particular requirements, provisions, deviations from extant
Railway Group Standards and Network Rail standards, or variations
on standard industry practice shall be stated and justified on the
Approval in Principle (AIP) submission. Furthermore, where
appropriate, the Environmental Agency or the Scottish Environment
Protection Agency shall be consulted and agreement for the design,
construction work and the specifications for work and materials
obtained and documented before finalising the AIP submission.
5.2 Planning and liaison
5.2.1 Railway infrastructure managers and operators
A design shall take account of the requirements for the safe and
efficient operation of railway infrastructure during the
construction and commissioning of the structure. Thus, as
necessary, the designer shall liaise throughout the design process
with those responsible for managing and operating that
infrastructure.
5.2.2 External authorities and parties
A design shall take account of the requirements of authorities
and interested parties external to Network Rail, and so liaison
with representatives of these organisations might be required
throughout the design process. Arrangements for liaising with such
representatives shall be agreed with Network Rail prior to any
consultation regarding the proposed works.
Unless the designer is specifically delegated or permitted to do
so, Network Rail will liaise directly with the Office of Rail
Regulation (ORR) and all Notified Bodies.
5.2.3 Planning authorities
Unless the designer is specifically delegated or permitted to do
so, Network Rail will undertake all consultations with planning
authorities, and all contact with such authorities shall be
co-ordinated through Network Rail. Furthermore, without the prior
approval of Network Rail, no communication shall be made to other
parties regarding permitted development status or planning
approval.
Where applicable, the following shall be considered in the
design;
• permitted development status,
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• planning permission issues,
• materials and finishes,
• aesthetics,
• landscaping, and
• the possible effects of the proposed method of construction
and the timetable of the construction works - for example, on road
traffic and on those living or working close to the site.
5.2.4 Legal obligations and commercial liability issues
Unless specifically delegated to the designer, all legal
obligation and commercial liability issues shall be addressed by
Network Rail: these issues include;
• liabilities, easement and wayleaves,
• load-carrying obligations - with regard to both statutory and
safety requirements,
• establishing requirements for carriageway widths etc, and
• existing agreements regarding the maintenance, replacement and
renewal of infrastructure and services.
5.2.5 Mineral extraction and landfill
Planning and design issues regarding mineral extraction and
landfill shall be dealt with in accordance with NR/L3/CIV/037:
Managing the risk arising from mineral extraction and landfill
operations, and NR/L3/CIV/038: Managing the potential effects of
coal mining subsidence.
Arrangements for liaising with mine operators and the Coal
Authority, and with landfill operators shall be agreed with Network
Rail prior to the designer consulting these organisations.
5.2.6 Buried services
With regard to the identification, marking, recording, and
working safely in the vicinity of buried services, the design shall
meet the requirements of; NR/L1/AMG/1010: Policy on working safely
in the vicinity of buried services, NR/L2/AMG/1020: Buried services
data provision, NR/L2/AMG/1030: Working safely in the vicinity of
buried services, and NR/L2/AMG/1040: Buried services data
feedback.
The requirements of these standards shall be met when
undertaking field investigations.
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5.3 Health and Safety
The design shall take account of all reasonably foreseeable
effects of the construction, maintenance and operation of the
structure on the health and safety of site operatives, railway
passengers and personnel, and members of the public. Thus, for
example, consideration shall be given to;
• the provision of positions of safety and walkways alongside
the railway (as required by NR/SP/OHS/069: Lineside facilities for
personal safety), and
• specific requirements for maintaining railway
infrastructure.
5.4 Environmental considerations
The design shall take account of all reasonably foreseeable
effects of the construction, maintenance and operation of the
structure on the environment. Thus, for example, consideration
shall be given to;
• the effect on sensitive species,
• the generation and control of noise and dust during
construction,
• the generation, re-use and disposal of waste materials - so
far as is reasonably practicable the design shall aim to minimise
the amount of material that is to be disposed of: the re-use of
clayey soils and weak rocks (such as marls and shales) might
require particular construction methods and expedients (such as
treatment with cement),
• the management of water on the site - including the effect of
water on (a) train control and other safety critical equipment, (b)
the stability of existing Earthworks, and (c) the generation and
control of contaminated run-off,
• managing vegetation in accordance with NR/L1/TRK/05200:
Vegetation - the design shall address the risks associated with
allowing vegetation to grow unchecked, and
• the carbon footprint of the construction and use of the
structure.
6 Design objectives and situations
The fundamental objectives of a design are that the structure
will;
• throughout its intended design life (with appropriate degrees
of reliability) remain fit for the use required, sustain all the
actions and environmental influences likely to be imposed upon it
during its construction and use - within acceptable deformation
limits,
• have adequate stability, resistance, stiffness, serviceability
and durability,
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• have sufficient resilience, robustness and structural
redundancy to (a) withstand damage by accidents and events (such as
vehicle impact, vandalism, and human error in design and use)
disproportionate to their original cause, (b) have a low
sensitivity to hazards that it might be subjected to, (c) withstand
the accidental removal of a structural member, and (d) so far as is
reasonably practicable, provide adequate warning of collapse - for
example, by showing signs of structural distress or
deformation,
• be economic to construct, use and maintain,
• be readily accessible for routine examination and maintenance,
and
• in construction and use, generate only acceptable risks to (a)
the safe use or performance of railway infrastructure and (b) the
safety of the public at large; and cause minimal or no damage to
property and the environment.
Both short-term and long-term design situations shall be
considered, and the identification and definition of these
situations shall take account of the following.
1. The types of action imposed on and by the structure.
2. The general suitability of the ground for construction.
3. The extent and nature of the various types of fill, soil,
rock and structural members/elements/components that are modelled
in any analysis.
4. The environment at the site, and the possible changes in the
environment produced by the construction and use of the
structure.
5. The possible effect of the construction and use of the
structure on existing infrastructure.
6. The requirements for the safe and ready examination,
maintenance, and repair of the structure - such as ease of access
to the site, and the criticality and durability of hidden parts of
the structure.
For each design situation, it shall be verified that no relevant
limit state will be exceeded. In defining the limit states,
consideration shall be given to the following.
1. The characteristics of the site (including the ground, ground
water and environmental conditions).
2. The form, complexity and size of the structure and its
members/elements.
3. The static, transient and dynamic loads that will be applied
to and by the structure.
4. Potential failures of (a) the ground, and (b) structural
members/elements (and connections between them) - singly, in
combination and in sequence.
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5. Failures that can be generated or promoted by surface
erosion, scour, earthslips, rockfalls, particular geological
features (such as steep bedding planes, relict landslips, faults,
joints, fissures, cavities and other underground structures), and
ground movements (for example, due to excavations, mining works,
and the plastic deformation of soils).
6. The effect of a failure of the structure on any supported,
protected or associated infrastructure and adjacent land - such as
the track, lineside buildings, buried services and drainage
systems.
7. The sensitivity of the proposed structure and any adjacent
infrastructure to ground movements.
7 Design approach
7.1 Types
Verification that a limit state will not be exceeded shall be
based on one or more of the following.
1. The results of calculations (see 7.2).
2. Implementation of prescriptive measures (see 7.3).
3. Use of experimental models and load tests (see 7.4).
4. Application of the Observational Method or Observational
Approach (see 7.5).
7.2 Calculation
7.2.1 Components
Geotechnical design by calculation requires the selection or
determination of the following.
1. Actions.
2. Ground properties.
3. Geometric data.
4. Limiting values for deformations, deflections, cracks
etc.
5. Calculation model(s).
7.2.2 Actions
Although the values of some of the geotechnical actions can
change through a calculation, initial estimates of these can be
selected to initiate the calculation cycle.
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The effects of soil-structure interaction (such as wall
friction) shall be taken into account when determining the
actions.
The duration of actions shall be considered with reference to
the time-dependent properties of the ground and construction
materials, such as the permeability and compressibility of
fine-grained soils.
Particular consideration shall be given to the effects of the
following.
1. Actions that are applied repeatedly.
2. Actions with varying intensity.
3. Actions that produce a dynamic response in the structure
and/or the ground.
4. Water pressures.
7.2.3 Ground properties
The properties of soils and rocks shall be represented in design
calculations by quantified geotechnical parameters determined from
the results of tests (directly, or indirectly - by theory,
correlation or empiricism) and other relevant data. The results and
other data shall be directly relevant or interpreted according to
the limit state being considered.
Account shall be taken of the possible differences between the
ground properties represented by the geotechnical parameters and
those that govern the behaviour of the structure; for example, how
the fabric of the ground (such as laminations and fissures) and the
rate of loading affect differently the results of a test and the
behaviour of the structure. As necessary, factors shall be
introduced to (a) convert the results of tests into values that
represent the in situ behaviour of the ground for the limit state
being considered, and (b) take account of correlations used to
derive values from the results of tests.
7.2.4 Geometric data
Geometric data include the level and slope of the ground surface
and the interfaces between different strata; the level of ground
water, excavations, foundations, track, roads, and placed fill; and
the dimensions of the structure.
7.2.5 Limiting values
Limiting values of ground movements shall be specified for the
design of foundations, and retaining walls (abutments, wing walls
etc). It might also be necessary to define limiting values of
ground movement for the design of Earthworks, and remedial works to
these (see 10.4).
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The limiting values for differential movement shall be set such
that if any of the values were met they would not produce or
promote a limit state in an adjacent structure.
In selecting design values for ground movements, the following
shall be taken into account.
1. The structural form/system/type being considered and the
likely effect of ground movements on the safe use and performance
of the structure.
2. The characteristics of the ground and construction
materials.
3. The mode of deformation.
4. The likely rate of deformation, both during construction and
following the end of construction.
5. The level of confidence that can be put on the acceptability
of the design values.
In calculating differential ground movements, the following
shall be taken into account.
1. The variation in the properties of the ground.
2. The method and sequence of construction.
3. The magnitude and distribution of loading, both during
construction and following the end of construction.
4. The rate of ground movements.
5. The stiffness of the structure and ground, both during
construction and following the end of construction.
7.2.6 Calculation model
The calculation model shall be appropriate for the ground
conditions and limit state being considered, and describe
adequately the behaviour of the ground. The calculation may be
based on an analytical or numerical model or a semi-empirical
relationship, but in all cases, the calculation shall provide a
safe solution, and where necessary an appropriate model factor
shall be applied to provide an adequate level of conservatism in
design. Where no reliable model is available for the limit state
being considered, one or more of the following methods shall be
used to prevent that limit state from being exceeded.
1. Analysis of another limit state using appropriate values for
the factors.
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2. The implementation of prescriptive measures (see 7.3).
3. The use of load testing (see 7.4).
4. The use of the Observational Method or Observational Approach
(see 7.5).
7.3 Prescriptive measures
Prescriptive measures include the application of conventional
and proven conservative rules for defining the size and detail of
structural elements; the specification and use of materials; the
definition of construction methods and protection works; and
setting minimum standards for workmanship and maintenance.
7.4 Load testing
Where the results of tests on scale models are used in design,
due account should be taken of differences between the model and
the structure - including;
• the effect of scale on (a) the strains and stresses developed,
(b) the importance of flaws, cracks, and fabric of the soil/rock,
and (c) material properties that are dependent upon particle
size,
• the method of construction, such as for the compaction of fill
materials,
• the effect of the rate of construction and/or loading,
particularly on the response of the ground, and
• the ground conditions of the model and the site, such as the
heterogeneity and anisotropy of the soils.
7.5 Observational Method and Observational Approach
The Observational Method may be used where geotechnical
behaviour is difficult to predict: the requirements and details of
the Method are provided in BS EN 1997-1: Geotechnical design:
General rules. In this Method, the design is reviewed at planned
times/stages through construction and modified, as necessary, in
response to the results of those reviews.
A variant of that Method (the Observational Approach) that may
be used for designing remedial works to Earthworks is described in
NR/GN/CIV/801: The application of the Observational Approach to the
design of remedial works to Earthworks. The Observational Approach
was derived from but does not implement the full potential of the
Observational Method. This restraint is due to (a) the lack of a
simple and dependable method for calculating ground movements to
determine intervention levels, and (b) the limited experience of
defining and applying such levels to railway Earthworks. As with
the Observational Method, there are requirements and restrictions
on the use of the Observational Approach.
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8 Design Categories
The design objectives, situations and factors described in 6,
the design approach (see 7) and any other relevant information
shall be used to determine the minimum requirements for (a) the
extent and detail of geotechnical investigations, and (b) the
details of the checks required on the design and construction
work.
BS EN 1997-1 states that the required procedures for (a) and (b)
may be identified for one or other of the three Geotechnical
Categories.
Category 1 shall include only small and relatively simple
structures, where (i) there is a negligible risk of failure, and
(ii) the design requirements will be satisfied through comparable
experience and qualitative geotechnical investigations. The
procedures for this Category can comprise routine methods for
design and construction.
Category 2 shall include only conventional types of structure
where there is (i) no exceptional risk of failure, and (ii) no
exceptional ground or loading conditions. The procedures for this
Category can comprise routine methods for (a) field and laboratory
testing, (b) design, and (iii) construction. Most repair works
undertaken on Earthworks will fall into this Category.
Category 3 shall include structures, and parts of structures,
that do not fall into Category 1 or 2. This Category should include
very large, complex, or unusual structural forms/systems,
structures built on poor and/or difficult ground (for example,
sidelong ground with a history of ground movements, and areas where
there are solution features), and structures that might affect the
stability of existing tunnels.
Different Categories (and hence procedures) may be defined for
various stages of the design process (such as the design and the
design check) and for different parts of the structure. A
preliminary categorisation should be undertaken prior to the
geotechnical investigation, but the Category shall be checked and
changed (as necessary) at each stage of the design and construction
process.
The Design Check Category (or Categories) shall be defined on
the AIP submission (see NR/L2/CIV/003): where necessary details of
the methods to be used for (a) the extent and detail of
geotechnical investigations, and (b) the details of the checks
required on the design and construction work shall be defined on
the submission. In all cases, project-specific requirements for (a)
and (b) shall be stated in the Forms provided in NR/L2/CIV/003.
9 Design, construction and specification of geotechnical
projects
9.1 Introduction
An integrated approach to design, construction and the
specification of geotechnical projects shall be followed: Figure 1
shows the integrated approach based on the Structural Eurocodes and
their supporting EuroNorms.
The standards described in the Figure may be supported by other
publications: for the Eurocodes such publications are defined as
Non-Contradictory
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Complementary Information (NCCI) and these are listed in the
National Annex (NA) to the particular Eurocode. (For example, the
NCCI referenced in the UK NA for EN 1997 includes CIRIA Report
C580: Embedded retaining walls - guidance for economic design, and
the Design Manual for Roads and Bridges.) Parts of some of the
currently listed NCCI might conflict with the Eurocodes. In the
longer term, current UK national Codes of Practice for structural
design will be superseded by ‘compliant residual’ versions that
will provide only advisory complementary information to the
application of the Eurocodes. In the meantime, in the event of any
conflict, unless specific direction is given otherwise, the
requirements of the Eurocode shall be followed where they are used
for design.
Figure 1: Integrated design approach provided by the
EuroNorms
The Eurocodes, being design codes, do not provide much
information on construction practices and workmanship - as was the
case with the UK Codes of Practice that they replaced: much of this
information is now provided in Execution EuroNorms. These EuroNorm
can be relevant to construction forms for which no corresponding
instruction or guidance is given in the relevant Eurocode. Where
this occurs, it is permitted to use the existing UK national Codes
for design (perhaps in conjunction with the Execution EuroNorms).
For example, BS EN 1997 does not cover the design of reinforced
soil structures, and so BS 8006: Code of Practice for
strengthened/reinforced soils and other fills shall be used for
design of these. In all such cases, however, an integrated
Construction standards - the
Execution EuroNorms
Design standard for the particular type of
structure - such as BS EN 1992
Standard governing the
basis of structural design
- BS EN 1990
Geotechnical Project
Geotechnical design standard
- BS EN 1997 (Parts 1 and 2)
Standards and specifications for
construction materials - the
Product EuroNorms
Standard governing the
actions on structures - BS
EN 1991
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approach to the design, construction and specification of a
geotechnical project shall be followed: designs shall not be based
on an incoherent pick and mix selection from the UK Code of
Practice and the Eurocodes.
9.2 New designs
Where applicable, new designs shall be undertaken in accordance
with the suite of Structural Eurocodes, with geotechnical designs
following the requirements of BS EN 1997 (Parts 1 and 2) and the UK
National Annex and the NCCI to that Eurocode.
The following general assumptions are stated in BS EN 1990.
1. The choice of the structural system and the design of the
structure are made by appropriately qualified and experienced
personnel.
2. Execution is carried out by personnel having the appropriate
skill and experience.
3. Adequate supervision and quality control is provided during
execution of the work, i.e. in design offices, factories, plants,
and on site.
4. The construction materials and products are used as specified
in EN 1990 or in EN 1991 to EN 1999 or in the relevant execution
standards, or reference material or product specifications.
5. The structure will be adequately maintained.
6. The structure will be used in accordance with the design
assumptions.
Some of these assumptions are re-iterated and others are added
in other Eurocodes; and BS EN 1997-1 provides the following.
1. Data required for design are collected, reported and
interpreted by appropriately qualified personnel.
2. Structures are designed by appropriately qualified and
experienced personnel.
3. Adequate continuity and communication exists between the
personnel involved in data-collection, design and construction.
4. Adequate supervision and quality control are provided in
factories, in plants, and on site.
5. Execution is carried out according to the relevant standards
and specifications by personnel having the appropriate skill and
experience.
6. Construction materials and products are used as specified in
this standard or in the relevant material or product
specifications.
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7. The structure will be adequately maintained to maintain its
safety and serviceability for the designed service life.
8. The structure will be used for the purpose defined for the
design.
For all but a few instances, these assumptions will be met in
designing new structures, but the designer shall check that all the
relevant assumptions that underpin the application of the Eurocodes
are met. Where any of these assumptions are not met, the designer
shall provide full details of them on the Approval in Principle
(AIP) submission and state what actions have to be taken to deal
with any departure from them.
Although the Eurocodes can be applied to the design of
traditional and more innovative structural forms (and parts of
these), they cannot be applied without amendment or supplement (a)
to unusual forms of construction, or (b) to structures that have
unusual in-service conditions, or (c) where conditions preclude
normal checks to be made on construction works or on the
maintenance of the structure. Thus, although the principles
expounded in BS EN 1990 can be applied in the design of all but a
few structures, other considerations and requirements have to taken
into account in the design of particular forms of structure (such
as reinforced soil structures).
Where necessary, the designer shall state on the AIP submission
why it would be inappropriate to use the Eurocodes for new designs
and the basis and justification for adopting the alternative method
of design.
9.3 Structural Assessment
Note (4) of the Scope (1.1) of EN 1990 states that it ‘is
applicable for the structural appraisal of existing construction,
in developing the designs of repairs and alterations or in
assessing changes of use’. However, although a limit state partial
factor method can be used for designing such works, unless the
Eurocodes were used to design the original structure they should
not be used to determine the safe load carrying capacity of an
existing structure and, from this, determine the required
strengthening works for that structure.
In general, the methods used for undertaking a Structural
Assessment or for designing repair or strengthening works based on
the results of such an Assessment should continue to be governed by
Network Rail standards and other relevant standards. In many cases,
the most appropriate method will be one based on a back-analysis of
the performance of the structure.
The designer shall state on the AIP submission the basis and
justification for adopting the particular method for undertaking a
Structural Assessment, and for designing works based on the results
of that Assessment.
9.4 Repair, maintenance and emergency works
Many repair and maintenance works do not involve any substantial
design: most will fall into Geotechnical Category 1 (see 8), and
some will require only
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the definition of the materials used and the methods used to
handle and place them (for example, the replacement of slipped soil
on the slope by compacted granular fill). Following much the same
argument advanced in 9.3, in many cases the Eurocodes would not be
applicable to such works.
The AIP submission for repair and maintenance works shall state
and justify the design approach.
By their very nature, there might be insufficient time to fully
develop and check the design of emergency works: the details of
such works would usually follow what has been found to be
successful in similar cases - even if shown subsequently to be
overly conservative. There might be no need for further works to be
undertaken, but where necessary, and as soon as reasonably
practicable, a permanent solution shall be designed and put in
place in a timescale appropriate to the nature and severity of any
residual risk. The design and construction of a permanent solution
shall take account of the practicality and cost-effectiveness of
incorporating (or removing and replacing) parts of the emergency
works. The AIP submission for the permanent solution shall state
and justify (a) the incorporation, removal and replacement or
augmentation of the temporary solution, and (b) the design approach
used for the permanent works.
9.5 Standard Details and Designs
As part of the drive for greater efficiency, Network Rail has
developed, and continues to develop, Standard Designs and Details
(SDDs) for a wide range of commonly undertaken Civil Engineering
works. Details of the SDDs and the application of them are provided
in NR/L3/CIV/151: Technical Approval of Standard Details and
Designs for Civil Engineering works.
Some of the SDDs are based on UK Codes of Practice for
structural design that have been superseded (largely) by the
Eurocodes, but these SDDs may continue to be used.
The designer shall confirm on the AIP submission that
consideration has been given to using the SDDs for the works in
hand. Where SDDs are used, it shall be stated in the
project-specific Forms provided in NR/L2/CIV/003 that the design
has included all the necessary requirements for applying the
SDDs.
9.6 Specification
Where applicable, the specifications for the construction
methods, construction materials, test methods etc shall be based on
NR/L3/CIV/140: Model Clauses for Civil Engineering works. As
necessary, the relevant Clauses shall (a) be revised to take
account of changes in the references, and (b) modified and/or
supplemented to suit the specific requirements of the works and the
site.
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10 Design requirements
10.1 Design working life
Unless otherwise agreed or stated in the project specification,
the following minimum design working lives shall be adopted for
geotechnical structures - excepting foundations. (Note that a
different design life may be defined in the project requirements
specification.)
Type Geotechnical construction form/system Minimum design
working life (years)
1 All new structures - such as Earthworks, retaining walls,
abutments and wing walls and all types of buried structure (unless
covered in one of the following types).
120
2 Gabion walls (excepting Temporary works/structures). 60
3 Repair works, including rock bolting and soil nailing but
excluding ground anchorages. 60
4 All works involving the installation of ground anchorages
(excepting Temporary works/structures). 120
5 Temporary works/structures. 10
The design working life for a foundation shall be defined in the
project requirements specification. In defining the design working
life, consideration shall be given to the following.
1. The design working life of the supported structure.
2. Economy in the construction, maintenance and renewal of the
foundation.
3. The possible re-use of the foundation for supporting a
replaced structure(s).
4. The effect of ground movements on the safe use and
performance of the supported structure.
For some types of project, Network Rail will require the design
working life to be determined from a whole-life costing approach.
In such cases, cost estimates shall be obtained for various
solutions with different design lives to enable Network Rail to
make an informed decision on the most appropriate solution. The
considered solutions shall satisfy Network Rail’s current strategy
for the route and take account of route-specific parameters - such
as the type of route and the ease of access for construction and
maintenance works.
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10.2 Durability
At the design stage, the environmental conditions at the site
shall be assessed (in relation to the design working life of the
structure and the durability of the construction materials) to
determine any necessary provisions for protecting or providing
resistance to the structural members and elements.
In particular, the design shall take account of the
following.
1. For sites on or adjacent to DC electrified lines, the
potential effect of stray currents on the long-term durability of
buried metallic elements/components (such as ground anchorages,
soil nails, and dowels) and the consequences of a premature failure
of these.
2. The effects of a lineside fire on the performance of the
structural components (in particular, geosynthetics) and the
consequences of a premature failure of these.
10.3 Design loads
10.3.1 General
Unless otherwise agreed or stated in the project specification,
railway traffic, road traffic and surcharge loading shall be in
accordance with BS EN 1991-2: Traffic loads on bridges.
The design shall take into account all static, transient and
dynamic loads that will be applied to and by the structure, and any
changes in these loads - such as an increase in lateral earth
pressure, and negative skin friction developed on piles.
Consideration shall be given to variable actions acting alone
and also in combination with other actions.
Account should be taken of the loads on existing foundations
that could affect and/or be affected by the proposed construction
works; particular attention shall be given to foundations adjacent
to a Cutting.
10.3.2 Railway loading
The characteristic loads shall be multiplied by the load factor
(γQ) specified in National Annex to BS EN 1990: UK National Annex
to Eurocode. Basis of structural design (2002) + A1 (2005).
Where appropriate, allowance shall be made for reasonably
foreseeable changes in the magnitude, extent and distribution of
railway traffic loads - such as produced by track lifting and
realignment, and the laying of additional tracks.
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10.3.3 Load classification factor for rail traffic actions
In accordance with the Eurocodes, for the verification of the
limit states (including GEO, EQU and STR) the value of load
classification factor (α) shall be taken to be 1.10: this is to be
applied to the equivalent vertical loading for Earthworks and the
earth pressure effects due to rail traffic actions in accordance
with the requirements in EN1991-2 clauses 6.3.2(3)P and
6.3.6.4.
10.3.4 Surcharge loading
Unless otherwise specified or agreed, a characteristic surcharge
loading shall be applied (as a permanent action) to part or all of
the plan-projected area of (a) an Earthwork (including the cess)
and (b) ground supported by a retaining wall, wing wall, abutment
etc. that is not designed to carry railway traffic or road traffic
loading.
The selection of the surcharge loading shall take account of the
loads that might be generated by construction plant and maintenance
vehicles.
The loading shall be applied to give the most unfavourable
effect on the structural member/element under consideration.
10.3.5 Water pressures
The ground water regime at the site shall be established from
the site investigation; with particular attention given to local
site records and data from piezometers and standpipes.
The water pressures adopted in a design shall take account of
the following.
1. Seasonal and tidal variations.
2. Adverse water pressures produced by perched, artesian or
sub-artesian water tables that might reasonably be expected to
occur over the design working life of the structure.
3. Adverse weather conditions, such as prolonged periods of
precipitation.
4. Changes in the existing ground water conditions due to the
construction and use of the structure, and of any reasonably
foreseeable changes in the infrastructure in and around the site
(including changes in land use).
5. The possible leakage from mains water pipes, sewers etc. and
the blockage of drainage systems.
6. Surface water flows.
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10.4 Settlement limits for Earthworks
When considering the serviceability limit state for the design
of a new Embankment that carries railway traffic (and repair works
to such Embankments), unless otherwise stated and justified in the
AIP submission the following settlement limits shall be
adopted.
Time after opening to rail traffic following end of
construction
Maximum settlement after opening to rail traffic (measured at
survey
stations located in the cess) 4 weeks 15 mm 6 months 25 mm
cumulative 12 months 30 mm cumulative
Unless otherwise stated and justified in the AIP submission,
settlement shall be measured at survey stations installed at a
maximum spacing of 50 metres in the cess along the track at the
location of the works. At least three such stations shall be
installed, one of which shall lie beyond the extent of the
works.
Where necessary in the design of a new Cutting, and repair works
to a Cutting, the settlement limits shall be stated and justified
in the AIP submission. Such limits shall take account of the
location and susceptibility to settlement of any existing
structures, services and drainage systems that could be affected by
the construction of the Cutting. The arrangements for monitoring
the works shall be defined in the Forms provided in
NR/L2/CIV/003.
10.5 Geotechnical parameters
10.5.1 General
Geotechnical parameters shall be derived from a geotechnical
investigation (see 12).
Where the design or characteristic values of the geotechnical
parameters are sufficiently well established (for example, from
earlier field investigations and published data) the designer shall
state, in the AIP submission, the source of the information and
justify the adoption of the values. Values of the partial factors
that may be applied to the characteristic values of geotechnical
parameters are given in Annex A of BS EN 1997-1.
10.5.2 Soils
As necessary for the limit state being considered, design or
characteristic values shall be derived for the following.
1. Strength, stiffness and compressibility parameters for
drained and/or undrained conditions - supported by data from index
tests, particularly where there are few test results.
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2. Effective stress and total stress shear strength parameters
including both peak and residual values, and remoulded values where
soils are to be excavated and re-used as fill.
3. Chemical and electro-chemical parameters to determine the
aggressivity of the ground to construction materials.
Where permeability and/or consolidation parameters are required,
information on the heterogeneity, anisotropy and fabric of the
soils shall be obtained from the site investigation to help
determine the appropriate design or characteristic values.
10.5.3 Rocks
As necessary for the limit state being considered, design or
characteristic values shall be derived for the following.
1. Appropriate strength parameters for rocks, taking account of
the extent and orientation of joints and discontinuities and the
surface characteristics of these (such as, roughness, aperture and
nature of the infill) and the water pressures that are or might be
developed within them.
2. Shear strength parameters; as determined from direct shear
tests undertaken on either undisturbed samples aligned so that
shear takes place along a discontinuity, or on prepared samples
that model such conditions.
3. Geotechnical parameters derived using rock mass
classification systems.
11 Particular requirements for various types of structures
11.1 Soil slopes
The design shall consider the potential effects on the stability
and serviceability of a soil slope (and any adjacent
infrastructure) of the following.
1. Weathering of exposed soils (including the effect of
freeze/thaw cycles) - and, from this, the need to protect the
surface against degradation.
2. Prolonged periods of wet weather following the removal of
vegetation - and, from this, the need and urgency for topsoiling
and vegetating the slope.
3. The permeability of exposed faces.
4. Fluctuations in the groundwater table.
5. Seepage.
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6. Existing and proposed drainage systems.
7. Seasonal swelling and shrinkage of clayey soils.
The designer shall consider the need for the following.
1. Installing lined interceptor drains or collector drains at
the top of a slope to reduce the risk of surface erosion and/or
slope instability.
2. On slopes steeper than 30 degrees, the use of geosynthetics,
erosion mats, hydroseeding or planting to form a vegetation
envelope.
For Cuttings through over-consolidated clay(s), the design shall
also take account of the potential effects of the following.
1. Softening of the clay due to long-term changes in pore water
pressure.
2. Widening of fissures due to stress relief.
3. Shrinkage of the clay (through drying) on the side
slopes.
The design of Earthworks on sidelong ground shall consider the
possible presence of solifluction deposits, relict landslides etc.
which could affect the stability of the Earthwork.
11.2 Rock slopes
For the design of rock slopes, and remediation of these, a
risk-based approach using a rock mass classification system may be
used. The Rock Slope Hazard Index system, or other suitable method,
may be used for moderately weak rock or stronger. For design
purposes, weak rocks may be treated as a soil. Any rock mass
classification system proposed by the designer shall be identified
in the AIP submission.
Where appropriate, the design shall include analyses of (acting
singly and in composition);
• planar, wedge or toppling failure along single or intersecting
discontinuities,
• planar failure along weak seams and shear zones, and
• rotational failure in weak shattered or decomposed rocks.
The design shall consider the effects on the stability and
serviceability of a rock slope (and any adjacent infrastructure) of
the following.
1. Weathering of exposed rock (including the effect of
freeze/thaw cycles, and chemical changes) - and, from this, the
need to protect exposed surface against degradation.
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2. The impact of vegetation - in particular, root action.
3. The presence of water-filled tension cracks.
4. For weak rocks, long-term creep movements and their effects
on the degree of fissuring, permeability and strength.
The design of a rock Cutting shall include a detailed assessment
of the extent, alignment and characteristics of discontinuities and
their influence on the stability of the rock mass.
Whenever possible, the construction of Cuttings through scree
shall be avoided: but where it is unavoidable, the scree shall be
classified as a loose cohensionless material and appropriate
geotechnical parameters derived for design.
Where Cuttings require blasting or are likely to be subject to
substantial ground vibrations during construction, an assessment
shall be made of the likely impact of the construction operations
on the stability of the Cutting, the proximity and type of
neighbouring infrastructure (particularly occupied buildings) and
the tolerance/sensitivity of the local environment to noise and
vibration.
11.3 Soil slope strengthening and repair
Strengthening and repair works for Earthworks may include a
combination of the following.
1. Regrading of slopes.
2. Granular replacement of slipped material.
3. Installation or upgrading of drainage system.
4. Installation of berms. (a) Consideration shall be given to
utilising berms as access routes. (b) Berms shall be constructed
using free-draining fill or provided
with a drainage system to prevent the build up of pore water
pressure within the existing Earthwork and/or berm both during and
following the end of construction.
5. Installation of piles. (a) Full details of a proposal to
incorporate any special feature in the
design of piles, such as enlarged bases, shall be included in
the AIP submission.
(b) In considering a piled solution, account should be taken of
the proximity and type of neighbouring infrastructure (particularly
occupied buildings) and the tolerance/sensitivity of the local
environment to noise and vibration.
6. Shear trenches.
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7. Soil nailing. (a) The design shall consider the need for
including a geotextile,
geogrid or steel mesh to distribute the load between the anchor
heads, to prevent localised sloughing until vegetation is
established.
8. Grouting.
9. Lime, cement or chemical treatment.
10. Gabion walls. (a) Plastic gabion cages shall not be used on
sites where there is a
high risk of vandalism and/or fire damage. (b) Steel wire for
gabion cages shall be galvanised and/or PVC-
coated. In addition, where applicable, the wire shall be
resistant to degradation by immersion in sea or aggressive
water.
(c) The front faces of the gabions shall be designed with the
vertical joints staggered - as in running bond brickwork. Where
necessary, the rear face of gabions shall be provided with a
geotextile layer to prevent fines passing from the supported soil
into the cage.
11. Installation of scour prevention measures.
In all cases, consideration shall be given to the need for
monitoring the performance and interaction between the existing
Earthwork and the new construction to verify the stability and
serviceability of the works.
11.4 Rock slope strengthening and stabilisation
Measures for strengthening or stabilising rock slopes may
include one or more of the following.
1. Scaling.
2. Netting and/or chaining the surface. (a) The durability of
the netting/meshes etc (and the pins or bolts
used to tie it down) shall match the design working life of the
Cutting.
(b) The design shall include provision for access for removing
excess rock debris that could accumulate within or behind the
netting and/or at the base of the Cutting.
3. Construction of catchment ditch, trap or fencing. (a) Where
necessary, on constrained sites the design shall
incorporate an outer fence or wall.
4. Installation of rock bolts, dowels etc.
5. Sprayied concrete.
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(a) Where sprayed concrete is used to span between rock bolts
(or similar structural supports) it shall be reinforced with a
steel mesh and that mesh shall be attached to the bolts prior to
spraying.
6. Buttressing. (a) Where necessary, buttresses and their
supports shall be provided
with drains to prevent the build-up of pore water pressures in
the fissures covered by the buttress.
7. Dentition.
8. Installation or upgrading of drainage system. (a) The design
shall take account of the recommendations given in
Rock Slope Engineering.
The design, detailing and construction of the above measures
shall follow industry good practice.
11.5 Earthworks subject to flowing water
The design of Earthworks (and repairs of these) in river,
coastal, estuarine and marine environments shall consider the
effects of scour and hydraulic action (including buoyancy and rapid
drawdown), and the need for and the specification of protective
works. In assessing these effects, the analysis shall assume the
maximum flood level that can be reasonably foreseen over the design
working life of the structure.
11.6 Shallow foundations
In determining the bearing capacity, sliding and overturning
resistance, and resisting passive pressures of spread, strip and
pad foundations, due account shall be taken of the likelihood and
severity of; unplanned excavations in and and around the foundation
(to install services for example); loss of support (produced by
scour or land slip for example), surcharge loading (generated by
overfilling and construction plant for example), and the effect of
weathering on the properties of the subsoils. In a design,
consideration shall be given to the characteristics of the site (in
particular the presence of sloping ground and existing services)
and the sensitivity of the structure to ground movements.
11.7 Excavations
The design shall include a check on the effect of excavations
(temporary or permanent) on the stability and serviceability of all
adjacent infrastructure. (Excavations include shear trenches,
drainage ditches, catchment ditches and traps, drainage trenches
and service trenches.)
The stability of excavations for the installation of services,
drains and over-excavation below formation level shall be checked
for a minimum depth of 0.5 metres.
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The location of excavations deeper than 0.5 metres shall be
identified in the AIP submission.
The limit on the length of excavation assumed in the design
shall be stated on the AIP submission.
Where relevant, the design of deep drainage trenches shall
include an assessment of the short-term stability and stand-up time
of the unsupported trench.
The Designer shall make reasonable assumptions regarding the
depth of unplanned excavations, the development of stabilising
passive pressures, and the likelihood of surcharge loading being
developed adjacent to an excavation (for example, produced by the
deposition of excavated soil). In general, in the design of
Geotechnical Category 2 and 3 works (foundations and retaining
walls) (see 8) it is good practice to allow for a 0.5 metre minimum
depth of excavation.
11.8 Drainage systems
The design shall consider the requirements for both temporary
and permanent measures for controlling surface and ground water to
maintain the stability of the construction works (such as
excavations) and the as-built structure. Account shall be taken of
any predicted or reasonably foreseeable long-term rise in the
groundwater table.
Drainage systems shall be designed for ease of maintenance and
renewal during the design working life of the structure.
Drainage systems should (a) be designed with positive falls to
prevent ponding, and (b) include provision of suitable discharge
outfalls or soakaways.
The design of drainage systems shall be in accordance with
NR/L3/CIV/005: Railway drainage manual.
11.9 Retaining walls
The geotechnical design of a retaining wall shall take account
of (inter alia);
• compaction forces generated on the back of the wall,
• the ground water regime and drainage system in and around the
wall, and the location, and potential leakage from, mains water
supplies,
• the potential temporary storage of materials (such as fill
materials) on the retained side,
• the excavation of trenches (for the installation of services
for example) at the front of the wall, and
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• the effect of weathering on the properties of the soils (both
retained and retaining).
The Designer shall consider the above points in determining the
lateral active and pressures pressures acting on a retaining wall.
In general, in the design of Geotechnical Category 2 and 3 works
(see 8) it is good practice to allow for a 0.5 metre minimum depth
of excavation in front of a retaining wall.
11.10 Dewatering
Whenever possible, dewatering works shall including a cut-off to
prevent lowering of the adjacent water table. However, where
dewatering will modify the level of the water table the design
shall assess the effects of drawdown (including settlement) on the
stability and serviceability of the structure and any other
infrastructure that might be affected. The results of the analysis
shall be included with the Forms provided in NR/L2/CIV/003.
11.11 Helical pile foundations for equipment support
structures
11.11.1 General
Helical screw piles generally comprise a lead section
(comprising helix plates attached to a central steel shaft) and
extension sections. At least two helices shall be provided on such
piles, but at least three helices shall be provided where the
capacity of the pile is dependent on the strength of heterogeneous
ground - such as interbedded soils and fill materials of variable
consistency.
The use of heavily loaded single piles shall be avoided: a pile
group should be used instead. Further, a single pile shall not be
used for sustaining a tension load from an inclined Overhead Line
Equipment stay.
11.11.2 Design
The Geotechnical Category for the various stages of the design
process shall be defined in the AIP submission. For most
applications, it would be appropriate to adopt Geotechnical
Category 2 (see 8) for the design and the design check.
The design methodology shall be stated on the AIP submission:
this shall include, as applicable, the source of the design data;
and the limit states, load cases, loads, limiting settlements and
safety factors used in the design.
The design may be verified by testing through installation using
an empirical relationship between pile capacity and torque
measurements, but acceptance of the relationship shall have been
confirmed at the design approval stage.
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The following issues shall be considered in design, and where
necessary details of how they have been dealt with stated and
justified in the AIP submission.
1. Creep of the piles under sustained loading.
2. Variable loading conditions, particularly where the
in-service load in a pile can alternate between tension and
compression.
3. The effect of wind loading; in general, wind loading should
not exceed 25% of the tensile resistance of a pile.
4. The limiting total and residual deflections of a pile (or
group of piles) at both the working load and proof load: these can
be set by the tolerable total and differential movements of the
equipment support structure.
5. The long-term design load that can be supported by a pile
embedded in a cohesive soil: this should be based on ‘drained’
design values of the soil.
6. Aggressive ground conditions.
7. Minimum depth of embedment in the bearing stratum. Note that
the validity of applying bearing capacity theory to a helix subject
to an uplift force is dependent upon the helix being sufficiently
embedded in the stratum.
11.11.3 Construction
The minimum spacing between piles should be three pile
diameters.
Where one or more piles in a group could be subject to a
permanent uplift force, a minimum of four piles should be installed
(on a square grid pattern) and connected to a pile cap
structure.
Consideration shall be given to the positioning of and
clearances of pile cap structures; such structures should not
obstruct cess path walkways, disrupt cable trough routes, or
interfere with track maintenance work. Where necessary, the means
of dealing with such issues shall be addressed in the AIP
submission.
The tolerance on the plan position for piles shall be 75 mm in
any direction: the pile cap structure should be designed to
accommodate these tolerances.
11.11.4 Termination
The mean installation torque measured over the final 1 metre of
installation should be used to check compliance with the design
torque requirements.
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Where the torsional strength rating of the central steel shaft
has been reached prior to achieving the design depth required, the
following options are open to the installer.
1. Terminate the installation at the depth reached.
2. Remove the pile and install a new one with smaller diameter
helices, or fewer plates, or a larger diameter shaft.
Where the design installation torque is not achieved at the
intended depth, the following options are open to the
installer.
3. Increase the depth of penetration, by adding further
extension sections, until the required torque is achieved.
4. Remove the pile and install a new one with additional and/or
larger diameter plates.
Consideration should be given to relocating the foundation where
(a) the design depth or installation torque has not been achieved,
or (b) an obstruction is encountered during installation.
Any changes to the design of the piles (such as for 1 to 4
above) shall be subject to review and acceptance by the Employer’s
Representative.
11.11.5 Pile testing
A planned programme of tests shall be stated on the AIP
submission. The number of tests should vary according to;
• the number of piles,
• the ground conditions at the particular site,
• the working and ultimate loads,
• comparable experience of the use of the piles, and
• the variability of the ground - a more intense programme shall
be considered where the helices are embedded in or adjacent to fill
materials of variable consistency.
The programme shall be reviewed, and amended according to the
results of the tests, throughout the project.
Tests on groups of piles rather than single piles may be
acceptable: the details and justification of such tests shall be
provided on the AIP submission.
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Testing shall be undertaken in accordance with the ICE
Specification for piling and embedded retaining walls with
variations introduced by the specification for the works (through
the Model Clauses).
12 Geotechnical investigations
12.1 General
The design shall be based on the findings of geotechnical
investigations, which comprise a gathering of all relevant
information about the site and a site investigation; the latter
comprises a desk study; field investigations; and laboratory
testing. The scale and cost of an investigation should vary (inter
alia) according to the types and characteristics of the ground
likely to be encountered; the availability and reliability of
existing geotechnical information about the site; and the Category,
size, type and cost of the structure being designed.
In some cases, a desk study (perhaps with a limited amount of
field investigation) might be sufficient; for example, for;
• Geotechnical Category 1 projects where the ground conditions,
ground-water regime and geotechnical parameters are sufficiently
well known from previous investigations, and
• projects involving the installation of foundations along an
extended length of the railway, where ground conditions are
reasonably consistent and known.
Where necessary, details of the test programme shall be agreed
with Network Rail prior to commencing any field investigation (see
5.2).
12.2 Ground investigation
Requirements for ground investigations and testing of soils are
given in BS EN 1997-2: Geotechnical design: Ground investigations
and testing and that standard describes the framework for selecting
the values of the geotechnical properties. Such values may be
derived from;
a) site investigations (including ones previously undertaken at
the site),
b) published data,
c) a combination of a). and b).
Many of the processes for obtaining values for the geotechnical
parameters are defined in various parts of the Structural Eurocodes
and in supporting standards: for example, Geotechnical
investigation and testing is covered in BS EN ISO 14688-1 and BS EN
ISO 14688-2 [for soils], and BS EN ISO 14689-1 [for rocks]. Further
parts of these and other European standards will be produced to
replace existing UK national standards (such as BS 5930 and parts
of BS 1377). Thus a definitive, complete list of applicable
standards
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cannot be provided herein. Nonetheless, ground investigations
shall be undertaken in accordance with current and most relevant
standards. Where necessary, a field investigation shall be
undertaken to (inter alia);
• identify likely failure mechanisms,
• obtain adequate information on the engineering and
physio-chemical properties of soils, fill and groundwater, and
• identify, remove and/or manage the uncertainties and risks
associated with the ground such as the existence of pre-existing
shear surfaces; the depth and degree of weathering, variations in
soil parameters; and the presence of aggressive agents to
construction materials.
For some sites, it will be necessary to undertake a contaminated
land survey to obtain information and data to;
a) devise safe methods of working for the construction
workforce,
b) obtain waste licensing agreement - where off-site disposal of
materials is required,
c) design measures to prevent contamination of water courses,
and
d) complete risk assessments for a) to c).
Where required, sampling and testing of contaminated soils and
groundwater shall be undertaken in accordance with BS 10175: Code
of Practice on investigation of potentially contaminated sites and
BS ISO 5667-11, BS 6068.11: Water quality. Sampling. Guidance on
sampling of groundwaters.
It may not be practicable to undertake a field investigation
prior to constructing emergency works; in such cases, the design
may be based on parameters derived from comparable experience.
However, where necessary, an investigation shall be carried out as
soon as is reasonably practicable to check the adequacy of the
emergency works.
12.3 Ground Investigation Report
In accordance with BS EN 1997, the results of the geotechnical
investigation shall be presented in a Geotechnical Investigation
Report (GIR). This report shall;
• present all the geotechnical information, including geological
features,
• provide a factual account of all field investigations and
laboratory tests,
• provide an interpretation of the information, including any
assumptions made in interpreting the results of tests,
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