Network Rail Standards - Programme Officersprogrammeofficers.co.uk/Preston/CoreDocuments/LCC130.pdf · 2018. 7. 21. · retaining walls; the foundations, piers, abutments and wing

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Reference NR/L3/CIV/071 Issue 4 Publication date 4th June 2011 Compliance date 3rd September 2011

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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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Reference NR/L3/CIV/071 Issue 4 Publication date 4th June 2011 Compliance date 3rd Se