DMRB VOLUME 2 SECTION 2 PART 6 - BD 12/01 - DESIGN OF ...

DESIGN MANUAL FOR ROADS AND BRIDGES

SUMMARY OF CORRECTION – BD 12/01 Volume 2, Section 2, Part 6DESIGN OF CORRUGATED STEEL BURIED STRUCTURES WITH SPANS GREATER THAN 0.9METRES AND UP TO 8.0 METRES

In November 2001, page 7/1 – 7/2, was issued incorrectly. (The page number was incorrect as itread 7/1 – 7/4). Please amend this page by crossing out page number 7/4, and writing 7/2.

November 2001


VOLUME 2 HIGHWAY STRUCTURESDESIGN:(SUBSTRUCTURES,SPECIAL STRUCTURESAND MATERIALS)

SECTION 2 SPECIAL STRUCTURES

PART 6

BD 12/01

DESIGN OF CORRUGATED STEELBURIED STRUCTURES WITH SPANSGREATER THAN 0.9 METRES AND UPTO 8.0 METRES

SUMMARY

This Standard covers the design and constructionrequirements for corrugated steel buried structures withspans greater than 0.9 metres and up to 8.0 metres.

INSTRUCTIONS FOR USE

This revised Standard is to be incorporated in theManual.

1. This document supersedes BD 12/95, which isnow withdrawn.

2. Remove existing contents page for Volume 2 andinsert new contents page for Volume 2 datedNovember 2001.

3. Remove BD 12/95, which is superseded byBD 12/01, and archive as appropriate.

4. Insert BD 12/01 in Volume 2, Section 2, Part 6.

5. Archive this sheet as appropriate.

Note: A quarterly index with a full set of VolumeContents Pages is available separately from TheStationery Office Ltd.

BD 12/01

Design of Corrugated SteelBuried Structures with SpansGreater Than 0.9 Metres and

up to 8.0 Metres

Summary: This Standard covers the design and construction requirements for corrugatedsteel buried structures with spans greater than 0.9 metres and up to 8.0metres.


THE HIGHWAYS AGENCY

SCOTTISH EXECUTIVE DEVELOPMENT DEPARTMENT

THE NATIONAL ASSEMBLY FOR WALESCYNULLIAD CENEDLAETHOL CYMRU

THE DEPARTMENT FOR REGIONAL DEVELOPMENTNORTHERN IRELAND

Volume 2 Section 2Part 6 BD 12/01

November 2001

REGISTRATION OF AMENDMENTS

Amend Page No Signature & Date of Amend Page No Signature & Date ofNo incorporation of No incorporation of

amendments amendments

Registration of Amendments

VOLUME 2 HIGHWAY STRUCTURESDESIGN:(SUBSTRUCTURES,SPECIAL STRUCTURESAND MATERIALS)

SECTION 2 SPECIAL STRUCTURES

PART 6

BD 12/01

DESIGN OF CORRUGATED STEELBURIED STRUCTURES WITH SPANSGREATER THAN 0.9 METRES AND UPTO 8.0 METRES

Contents

Chapter

1. Introduction2. Design Principles3. Design Loads4. Design Load Effects5. Strength Parameters6. Ultimate Limit State Requirements7. Serviceability Limit State Requirements8. Durability9. Excavation and Filling10. Handling and Installation11. End Treatment12. Overlying Reinforced Concrete Slab13. Concrete Invert Paving for Closed Invert

Structures14. Carriageway Drainage15. Multiple Installations16. Technical Requirements and Design Checklist17. References18. Enquiries

Annex A Procedure and Conditions for Obtaining aType Approval Certificate for CorrugatedSteel Buried Structures

Annex B Longitudinal Seam Strength for BoltedSegmental Structures

Annex C Specification for Tensile Strength ofLockseams in Helically Wound CorrugatedSteel Structures


November 2001


November 2001 1/1

Chapter 1Introduction

1. INTRODUCTION

1.1 This Standard gives the design and constructionrequirements for corrugated steel buried structures thatact compositely with the surrounding material to resistloading. It describes the procedures to be followed thatpermit the Contractor to choose a proprietary structurethat meets the Overseeing Organisation’s requirements.It follows the principles of BD 12/95 and requires acurrent Type Approval Certificate for all corrugatedsteel buried structures, updates durability requirementsand clarifies the requirements in regard to excavationand filling, handling and installation and end treatment.Further clarification is made to the presentation of theformulae given in this document.

Equivalence

1.2 The construction of corrugated steel buriedstructures will normally be carried out undercontracts incorporating the Specification forHighway Works (MCHW1). In such cases productsconforming to equivalent standards or technicalspecifications of other states of the EuropeanEconomic Area and tests undertaken in other statesof the European Economic Area will be acceptablein accordance with the terms of Clauses 104 and105 in Series 100 of that Specification. Anycontract not containing these Clauses must containsuitable clauses of mutual recognition having thesame effect regarding which advice should besought.

Scope

1.3 This Standard covers bolted segmentalcorrugated steel buried structures, with spansgreater than 0.9 metres and up to 8 metres, whichare straight in plan, and which are of:

bolted segmental construction with cross sectionsbeing:

(i) closed circular

(ii) closed multi-radii

(iii) circular arch; or

helically wound construction with cross sectionsbeing:

(i) closed circular

subject to the following requirements:

a. The size and shape are within the limitsspecified in Table 1.1.

b. The depth of cover measured from thefinished road surface or final ground level tothe crown of the structure is not less thanspan/5 or 650mm whichever is greater.However, where a reinforced concrete slabis provided at finished road surface, a lesserdepth of cover will be acceptable (seeClause 12.1 below).

c. The environment is “non-aggressive” or“aggressive” as defined in Chapter 8. Anenvironment which is classed as “veryaggressive” is outside the scope of thisStandard and specialist advice should besought.


November 20011/2


This Standard does not cover the use of corrugatedsteel buried structures in the repair of other typesof structure, for example, as a liner for brick archstructures. In these situations, specialist adviceshould be sought from the manufacturers ofcorrugated steel structures.

Environmental Considerations

1.4 The Overseeing Organisation’s requirementsfor environmental design shall be taken intoaccount in designing corrugated steel buriedstructures. Volume 10 of DMRB (EnvironmentalDesign) gives advice on the use of underpasses bymultiple species of small mammals and fish. Itillustrates various forms of culvert design tofacilitate free passage of these species. Often theseconsiderations are fundamental to thedetermination of the span, headroom, cross-sectioninvert and gradient of the structure.

Approval Procedure

1.5 Corrugated steel buried structures areproprietary manufactured structures and the designand contractual procedures required by StandardSD4 (MCHW 0.2.4) shall be followed.

1.6 All bolted segmental and helically woundcorrugated steel buried structures and theircomponents require a current Type ApprovalCertificate (MCHW1 Clause 104.9). Helicallywound corrugated steel buried structures and theircomponents shall also have a current British Boardof Agrément, Roads and Bridges, Certificate orequivalent (MCHW1 Clauses 104.5 and 104.6) forthe end-use described in this Standard. The BritishBoard of Agrément (BBA) Certificate orequivalent shall include guaranteed minimumlockseam tensile strengths satisfying therequirements of Annex C of this Standard.

1.7 Prior to being offered on a Contract, themanufacturer of the corrugated steel buriedstructure shall have obtained a Type ApprovalCertificate from The Highways Agency. Theprocedure for obtaining the Type ApprovalCertificate for bolted segmental structures isdescribed at Annex A. The procedure for obtainingthe Type Approval Certificate for helically woundstructures is also as described at Annex A andcurrent certification by the British Board ofAgrément is mandatory.

1.8 Where the Contractor proposes a proprietarysystem of invert protection, the proprietary invertsystem shall have a current British Board ofAgrément Roads and Bridges Certificate orequivalent for the end-use as indicated in theSchedule of Employer’s Requirements included inthe Outline Approval in Principle.

1.9 Where the Contractor chooses a proprietaryprotection coating with a designated life intendedto contribute towards the durability requirement ofthe structure, a current British Board of AgrémentRoads and Bridges Certificate or equivalent shallbe provided confirming its life under serviceconditions appropriate to the circumstances statedin the Schedule of Employer’s Requirements.

1.10 The materials used for corrugated steelburied structures, their manufacture and theirassembly and construction on site shall be inaccordance with the Specification for HighwayWorks (MCHW1).

Contract/Design Procedure

1.11 A flow diagram for a typical contract/designprocedure is given in Figure 1.1 to assist users of thisStandard.

Implementation

1.12 This Standard shall be used forthwith on allschemes for the construction and improvement oftrunk roads, including motorways, currently beingprepared, provided that, in the opinion of theOverseeing Organisation this would not result insignificant additional expense or delay. DesignOrganisations shall confirm its application toparticular schemes with the OverseeingOrganisation. In Northern Ireland the use of thisstandard shall apply on those roads designated bythe Overseeing Organisation.

Mandatory Requirements

1.13 Sections of this document which form mandatoryrequirements of the Overseeing Organisation arehighlighted by being contained within boxes. Theremainder of the document contains advice andenlargement which is commended to designers for theirconsideration.


November 2001

Symbols

1.14 The symbols used in this Standard are defined asfollows:

a (mm²/mm) Cross-sectional area of corrugatedsteel per unit length, the crosssection being parallel to the lengthof the structure.

aa (mm²/mm) Adjusted cross-sectional area of

corrugated steel per unit lengthbased on the remaining wallthickness after deduction ofsacrificial metal thickness requiredby Chapter 8.

B (mm) Diameter of plate used in plate loadtest.

C (kN/m) Compressive hoop load in the wallof the structure per unit length.

CT (kN/m) Total compressive hoop load in the

wall of the circular arch structureper unit length acting upon thefoundation.

dc (mm) Depth of corrugation.

D (mm) Additional trench width required forcircular arch structures.

E (N/mm²) Modulus of elasticity of thestructural steel.

Es(N/mm²) Modulus of elasticity of the soil.

F(mm/N) Flexibility factor.

Fmax

(mm/N) Limiting value of flexibility factor.

fa(N/mm²) Compressive hoop stress.

fb(N/mm²) Theoretical transverse elastic

buckling stress.

fc(N/mm²) Nominal allowable buckling stress.

fs(N/mm²) Stress derived from adjusted

nominal seam strength (kN/m) basedon the remaining wall thicknessafter deduction of sacrificial metalthickness required in Chapter 8.

fy(N/mm²) Minimum yield strength of the steel.

h(m) Nominal height of fill above thestructure.

ht(m) Height of fill above the crown of the

structure including the thickness ofany road construction.

I(mm4/mm) Cross-sectional moment of inertia ofthe corrugated steel per unit length,the cross-section being parallel tothe length of the structure.

Ia (mm4/mm) Adjusted cross-sectional second

moment of area of the corrugatedsteel per unit length, the cross-section being parallel to the lengthof the structure.

Id

Depth correction factor for plateload test.

k(N/mm³) Coefficient of soil reaction.

ke(N/mm³) Modified coefficient of soil reaction.

K Constant.

Ka

Active earth pressure coefficient.

m Poisson’s ratio of the structuralsteel.

M*(N/mm²) Constrained soil modulus.

mv(mm²/N) Coefficient of volume

compressibility.

N Uncorrected SPT value.

P(kN/m²) Radial soil pressure on a circularclosed invert structure.

Pb(kN/m²) Radial soil pressure on the bottom of

a multi-radii structure.

Pc(kN/m²) Radial soil pressure on the corner of

a multi-radii structure.

Pt(kN/m²) Radial soil pressure on the top of a

multi-radii structure.

Pd(kN/m²) Design vertical superimposed dead

load pressure.

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November 2001

PL(kN/m²) Design vertical live load pressure.

P1 (kN/m²) Overburden pressure on top of

footing of circular arch.

P2 (kN/m²) Lateral earth pressure on the outside

face of the footing of a circular arch.

P3 (kN/m²) Overburden pressure on top of

footing inside circular arch.

Q* Design Loads (Refer to BS 5400:Part 1).

r(m) Radius of circular structure.

rb(m) Radius at the bottom of a multi-radii

structure.

rc(m) Radius at the corner of a multi-radii

structure.

rt(m) Radius at the top of a multi-radii

structure.

R* Design Resistance (Refer toBS 5400: Part 1).

S (m) Span of the structure (diameter ofcircular structure).

S* Design Load Effects (Refer toBS 5400: Part 1).

t (years) Life of sacrificial thickness of steel.

T(µm) Thickness of sacrificial metal foreach corroding face.

Wf (kN/m) Self weight of foundation per unit

length.

y (m) Excavation width measured from thewalls of the structure.

Z1(m) Depth from road surface/ground

level to top of foundation.

Z2(m) Depth from road surface/ground

level to mid height of foundation.

γ(kN/m³) Bulk unit weight of compacted fill.

γfL

Partial safety factor that takesaccount of the possibility ofunfavourable deviation of the loadsfrom their nominal values and of thereduced probability that variousloadings acting together will allattain their nominal valuessimultaneously.

γf3

Partial safety factor that takesaccount of inaccurate assessment ofthe effects of loading, unforeseenstress distribution in the structure,and variations of dimensionalaccuracy achieved in construction.

γm

Partial safety factor that takesaccount of variabilities in materialstrength and uncertainties in theassessment of component strength.

∆q (N/mm²) Change in pressure applied by the

plate (plate load test).

∆s (mm) Change in average settlement of the

plate (plate load test).

∆x (m) Increase in horizontal diameter or

span.

θ Re-entry angle of circular archmeasured between the vertical andthe tangent to the arch wall at thetop of the foundation.

ν Poisson’s ratio of the soil.

1/4



November 2001

Initial Feasibility Study and Assessment ofEmployer’s Requirements in Chapter 16

by Design Organisation

Ensure Structure initially complies with the following Sections:

a) Introduction/Scope - Chapter 1b) Handling Installation - Chapter 10c) End Treatment - Chapter 11d) Multiple Installations - Chapter 15

Determine ConstrainedSoil Modulus M*

Stiffness of Soil Surroundingthe Structure Clauses 5.1 - 5.8

of Chapter 5

Determine DurabilityRequirements in Chapter 8

Determine SacrificialMetal Thickness

For Corrugated Steel Product andGauge selected determine the

following:

Ia Adjusted cross-sectional moment of inertia

aa Adjusted cross-sectional area

fs Stress derived from adjusted nominal seam strength

Taking into account sacrificial metalloss Clauses 6.1 and 7.1

Determine Design Load Effects in Chapter 4

a) Compressive Hoop Stress - Clause 4.2

b) Radial Soil Pressure forClosed Invert Structures - Clause 4.3

c) Foundation Loading forCircular Arches - Clause 4.4

Ensure Compliance with Design Requirements andStrength Parameters at Ultimate Limit State - Chapter 6

a) Buckling Capacity - Clause 6.2ab) Yield - Clause 6.2bc) Seam Strength - Clause 6.2cd) Stress Limits for Helically Wound Structures - Clause 6.2d

Design Organisation to discuss proposalswith TAA, obtain outline approval and

produce an outline design as appropriate,and incorporate into Contract Documents

Contractor/Manufacturer *seeks Approval in Principle from TAA andcarries out Design for Structure Proposed

and obtains Relevant Approvals

Determine Nominal BucklingStress from Clause 5.9 - 5.10 of

Chapter 5

Determine Design Loadsin Chapter 3Dead Loads

Superimposed Dead LoadsLive Loads

ContinuedOverleaf

* Outline Approval in Principle Form and Approval in Principle Form shall both incorporate thelistings of Employer’s Requirement as set out in Chapter 16

FEASIBILITY STUDYCOMPLETE

OUTLINE AIP ANDOUTLINE DESIGN

COMPLETE

Figure 1.1 Flow Diagram for Contract/Design Procedure

1/5



November 2001

Ensure Compliance with Design Requirements and at Serviceability Limit State - Chapter 7

a) Deflection - Clause 7.2 b) Allowable Net Bearing Pressure - Closed Invert Structures - Clause 7.3 & 7.4 c) Foundation Design - Circular Arches - Clause 7.5

Determine Requirements for Excavation and Filling Chapter 9

Trench - Figure 9.1 Partial Trench - Figure 9.2 Embankments - Clause 9.14

(Check also Figure 8.1 of Chapter 8 for durability requirements)

a) Design End Treament - Chapter11

b) Design Overlying Reinforced Concrete Slab (if required) - Chapter 12

c) Design Invert Paving for Closed Invert Structures (if required) - Chapter 13

d) Check detail of carriageway drainage in vicinity of structure (if required) - Chapter 14

Check of Final Design

Formal Approval of Design and Design Informationfor Construction

Contractor to Submit Final Design with DesignCertificate and Design Information required in

Chapter 16.

Determine, list and record informationrequired in Chapter 16

FEASIBILITY STUDY COMPLETE- PROCEED TO OUTLINE AIP

AND OUTLINE DESI GN

OUTLINE AIP & OUTLINEDESIGN COMPLETE,

CONTRACTOR TO PROCEED

Submission of As Constructed Information forMaintenance Manual as required in Chapter 16

Figure 1.1 Flow Diamgram for Contract/Design Procedure

Continued from Overleaf

1/6



November 2001 2/1

Chapter 2Design Principles

2. DESIGN PRINCIPLES

2.1 Limit state principles have been adopted fordesign in this Standard. The limit states adoptedare:

a. Ultimate limit states represented by:

i. The strength of the structure asdetermined by the yielding andbuckling behaviour of corrugated steelburied structures, and

ii. The strength of a longitudinal boltedseam as determined by tests on boltedplate assemblies.

b. Serviceability limit states represented by:

i. A limiting deflection expressed as amaximum percentage change in thespan dimension beyond which causefor public concern may be expectedand remedial action to protectivecoatings and finishings may berequired.

ii. The allowable net bearing pressure ofthe foundation material for closedinvert structures.

iii The allowable net bearing pressure ofthe foundation material beneath theconcrete foundations of circular archstructures.

2.2 Design loads (Q*) are expressed as theproduct of nominal loads and the partial safetyfactor γ

fL.

2.3 Design load effects (S*) are expressed as theproduct of the effects of the design loads and thepartial safety factor γ

f3.

2.4 Design resistance (R*) is expressed as thenominal strength of the component divided by thepartial safety factor γ

m.

2.5 The design load effects (S*) at the ultimatelimit state must not be greater than the designresistance (R*). In addition, at the serviceabilitylimit state the deflection must not be greater than

the limiting value given in this Standard and thesettlement of the foundation material must notadversely affect the performance of the structure.

2.6 As the allowable net bearing pressure of soilis not normally expressed in characteristic (ornominal) strength terms, the checks involvingallowable net bearing pressure shall be undertakenwith unfactored nominal loads.

2.7 For the ultimate limit state the followingload combinations shall be considered:

a. Dead Loads together with Live Loads.

b. Dead Loads together with TemporaryConstruction Loads.

2.8 For the serviceability limit state, DeadLoads shall be considered together with LiveLoads.

2.9 The steel section chosen for the walls of thestructure must satisfy both the strength anddeflection requirements of Chapters 6 and 7 andalso the durability requirements of Chapter 8 interms of sacrificial steel. The steel thicknessrequired to satisfy these criteria may be different atdifferent points around the circumference of thestructure. Care shall be taken during assembly toensure the correct positioning of plates of differentthickness.


November 2001 3/1

Chapter 3Design Loads

3. DESIGN LOADS

Dead Load of Steel

3.1 a) The self-weight of corrugated steelburied structures may be ignored forthe Ultimate Limit State requirementsand Serviceability Limit Staterequirements as defined in Chapter 6and Chapter 7 respectively.

b) During the construction, the self-weight of corrugated steel buriedstructures shall be considered iftemporary strutting or ties arerequired to support the structure.(Refer to Clause 10.5.)

c) In the case of end treatments, the self-weight of corrugated steel buriedstructures, including headwalls, ringbeams and collars etc, shall be takeninto account. (Refer to Chapter 11).

Values for γfL

are given in Table 3.1.

Superimposed Dead Load

3.2 The design vertical pressure on the structuredue to the superimposed dead load is given by:

Pd

= γfL

x nominal vertical pressure

= γfL

γh (kN/m²)

where γ = Bulk unit weight of compacted fill(kN/m³)

and h = Nominal height of fill above thestructure (m), to be taken ash

t + 0.25r for circular structures

and circular arches, and ht + 0.25r

tfor multi-radii structures

where ht

= Height of fill (m) above the crownof the structure, including thethickness of any road construction

r = Radius of closed circular structureor circular arch structure, (m)

rt

= Radius at the top of a multi-radiistructure, (m)

Values for γfL

are given in Table 3.1.

Live Loads

3.3 Nominal live loads shall be the HA or HBloading whichever is the more onerous, applied inaccordance with BS 5400: Part 2, as implementedby BD 37 (DMRB 1.3). HA loading shall consistof a single nominal wheel load of 100kN. HA UDLand KEL need not be considered. For Trunk Roadsincluding Motorways, HB loading shall consist ofa minimum of 45 units. For other classes of roadsrefer to BD 37. There is no requirement for co-existing HA and HB wheel loadings to beconsidered either in the same or adjacent lanes.

3.4 On the carriageway each wheel load shall beassumed to be uniformly distributed over a contactarea, circular or square in shape based on anominal tyre inflation pressure of 1.1N/mm².

3.5 To determine the nominal vertical live loadpressure, P

L on the structure due to any wheel load,

dispersion in three dimensions may be assumedfrom the limits of the contact area on thecarriageway to the level of the crown of the buriedstructure at a slope of 2 vertically to 1 horizontallyas shown in Figure 3.1. This pressure shall betaken to act over the whole span. A wheel load notdirectly over the structure shall be included if itsdispersion zone falls over any part of the structure.

3.6 In the case of the HB vehicle only, thedispersion zones of individual HB wheel loadsshall be combined and distributed jointly asindicated in Figure 3.1. This applies to adjacentwheels on the same axle and, where the span islarge enough, to wheels on succeeding axles.


November 20013/2


3.7 Where a reinforced concrete structural slab isproposed in accordance with Clause 1.3(b) and Clauses12.1 to 12.5 of this Standard, dispersion of any wheelload as described in Clause 3.5 may be assumed tooccur throughout the depth of the structural slab at aslope of 1 vertically to 1.5 horizontally. Below the levelof the bottom of the structural slab, dispersion of thewheel loads may be assumed to occur at a slope of2 vertically to 1 horizontally.

Alternatively, the nominal live load pressures acting onthe culvert may be assessed by a suitable multi-layerelastic analysis, using one of the methods given inChapter 6 of “Elastic Solutions for Soil and RockMechanics” by H G Poulos and E H Davis, (1) whichtakes into account the relative stiffness of the structuralslab and the layers of material between the slab and thecrown of the culvert.

3.8 The nominal vertical live load pressure onthe structure due to tracked construction vehiclesor large rubber tyred earthmoving vehicles shall bedetermined at a depth of cover of one fifth of thespan of the structure, or 1m, whichever is greater.

3.9 Braking loads and temperature effects shallbe ignored.

3.10 To obtain the design vertical live loadpressure, P

L (kN/m²), the nominal pressures shall

be multiplied by the appropriate values of γfL

givenin Table 3.1.


November 2001

LOAD SLS ULSγγγγγfL γγγγγfL

Dead Load Concrete, End 1.0 1.2Treatment Only (Chapter 11)

Dead Load, Corrugated Steel Only 1.0 1.2(Chapters 6 & 7 and Clause 10.5)

Superimposed Dead Loading 1.1 1.3

HA wheel load 1.2 1.5

HB loading 1.1 1.3

Temporary Construction Loading - 1.3

All loads for Radial Soil Pressure 1.0 -Calculation

All loads for determining thrust 1.0 -acting on circular arch foundationsfor bearing pressure calculation

SLS: Serviceability Limit State

ULS: Ultimate Limit State

Table 3.1 - γγγγγfL - Partial Safety Factors for Loads

3/3



November 2001

Chapter 4Design Load Effects

4/1

4. DESIGN LOAD EFFECTS

4.1 The design load effects involved in thedesign of the corrugated steel buried structurescovered by this Standard are the compressive hoopstress f

a (all structures) and the radial soil pressure

P (closed invert structures), which shall becalculated from the design load pressures using theformulae given below based on the ringcompression theory, where the compressive hoopstress in the wall of the structure is assumed to beuniform around its periphery and the radial soilpressure at any point is assumed to be inverselyproportional to the radius of curvature at that point.

4.2 Compressive Hoop Stress

Compressive hoop stress fa = C γ

f3 (N/mm²)

aa

Where C = Compressive hoop load in thewall of the structure per unitlength (see Figure 4.1)

= S (Pd + P

L) (kN/m)

2

S = Span of the structure (m)

Pd

= Design vertical superimposeddead load pressure at theultimate limit state (kN/m²)

PL

= Design vertical live loadpressure at the ultimate limitstate (kN/m²)

aa

= Adjusted cross-sectional areaof corrugated steel per unitlength, (mm²/mm) the crosssection being parallel to thelength of the structure. (Referto adjustments required inClause 6.1 and 7.1). If thecross-sectional area variesalong the length of thestructure, the minimum shallbe used, except that there-rolled ends of helicallywound culvert lengths shall notbe considered to affect the

cross-section unless theyextend for more than 250mm atthe end of each length.

γf3

= is to be taken as theappropriate value given inTable 4.1 for the particulartype of structure and the limitstate involved. The values inthe table take account of theinfluence of the relativestiffness of the particularstructural form, the amount ofdeformation occurring beforethe various limit states arereached, and the variation ofstress distribution in theparticular type of structure.


November 20014/2


4.3 Radial Soil Pressure for Closed InvertStructures

This shall be calculated as follows:

a. Circular Structures

External radial soil pressure

P = C = Pd + P

L (kN/m²)

r

b. Multi-radii

Radial soil pressure on the top

Pt

= C (kN/m²)r

t

Radial soil pressure on the corner

Pc

= C (kN/m²)r

c

Radial soil pressure on the bottom

Pb

= C (kN/m²)r

b

where C is as defined in Clause 4.2 but calculatedusing P

d and P

L from unfactored nominal loads (see

Clause 2.6)

r = Radius of circular structure (m)

rt

= Radius of the top (m) ) of Multi-) radii

rc

= Radius of the corner (m) ) structures) (see

rb

= Radius of the bottom (m) ) Figure) 4.2)

Reference should be made to Chapter 7, Clause 7.3for the allowable net bearing pressure of thefoundation material.

4.4 Strip Foundation Loading - CircularArches (Serviceability Limit State only)

(a) Thrust

The total thrust CT, in the wall of the structure,

acting upon the foundation at an inclined angle ofθ to the vertical is given by:

CT

= Cγf3 (kN/m)

where C is given in Clause 4.2except that P

D and P

L are at the

Serviceability Limit State and γf3 is given in

Table 4.1


November 2001

(b) Earth Pressure from Fill

The overburden pressure P1, on the top of the

footing is given by:

P1

= γf3 γZ

1 (kN/m²)

where Z1(m) is depth from road/ground level

to top of foundation, γ is unit weight ofoverburden (kN/m³), and γ

f3 = 1 for SLS

The lateral earth pressure, P2 acting on the outside

face of the footing is given by:

P2

= γf3 K

a γZ

2 (kN/m²)

where Z2(m) is depth from road/ground level

to mid height of foundation, Ka is active

earth pressure coefficient, and γf3 = 1 for

SLS

The lateral pressure acting on the inside face of thefooting may be ignored.

Vertical and horizontal pressures resulting fromlive loading surcharge on the carriageway may beignored when assessing P

1 and P

2.

Consideration shall be given to avoidingdifferential settlement between the foundation andthe side fill such that the side fill settles to agreater extent. This may cause the overburdenpressure on top of the footing to be larger than thecalculated P

1 value, and cause additional loading

on the foundation. Refer to Clause 7.5.

(c) Vertical Pressure on Inside Face

The vertical pressure on top of the footing, P3,

shall include any superimposed dead loadings. Thevertical pressure, P

3, shall also include any

nominal live loads due to vehicular, rail orpedestrian traffic and these nominal live loadsshall be in accordance with BS 5400: Part 2 asimplemented by BD 37 (DMRB 1.3).

(d) Self Weight

The self weight of the foundation is Wf per unit

length (kN/m).

(e) Allowable Net Bearing Pressure forFoundation Design

Reference shall be made to Chapter 7, Clause 7.5for the allowable net bearing pressure of thefoundation material.

4.5 Other Types of Foundations for CircularArches

Circular arch structures can also be constructed on asuitably designed base slab which supports both wallsof the structure simultaneously.

To reduce the effects of the lateral earth pressure P2,

and loads from the structure, struts may be adoptedbetween strip foundations.


4/3


November 2001


4/4

Values of γγγγγf3

Typeof ULS SLSStructure

Buckling Yield Seam Thrust onfoundations

Multi-radii and bolted circular 1.15 1.15 1.15 -closed invert

Circular Arch Profile, Type 1 1.15 1.53 1.53 1.3320° to 30° re-entry

Circular Arch Profile, Type 2 1.75 2.3 2.3 2.010° to 20° re-entry

Helically Wound 1.10 1.10 - -

Table 4.1 - γγγγγf3 Partial Safety Factors


November 2001

5. STRENGTH PARAMETERS

Constrained Soil Modulus

5.1 When the structure is to be installedpartially or wholly in trench the M* of existingmaterials, within a distance equal to the span oneach side of the structure, shall be determined,during the ground investigation for the scheme.Normally the method given in Clause 642MCHW1 shall be used for plate load testing, fornon-cohesive soils. Alternatively the methodsdescribed in 5.4 and 5.5 may be used, asappropriate, during the ground investigation.

5.2 The constrained soil modulus M* representsthe stiffness of the soil surrounding the structure,whether backfill or existing material and is givenby:

M* = (1 - ν) Es

(N/mm²)

(1 + ν) (1 - 2 ν)

where ν = Poisson’s ratio of the soil (to betaken as 0.3 when determining M*) andE

s = Modulus of elasticity of the soil

(N/mm²)

5.3 When carrying out plate load testing usingthe method given in Clause 642 MCHW1 for non-cohesive soils the Modulus of elasticity E

s of the

soil shall be determined used the formula:

Es

=

where B = diameter of plate used in the plateload test (mm)

∆q

= change in pressure applied by theplate (N/mm2)

∆s

= change in average settlement of theplate (mm)

Id

= depth correction factor (taken as1.0 when test complies withClause 642 MCHW1)

ν = Poisson’s ratio of the soil (to betaken as 0.3)

5.4 The M* for non-cohesive soils may bedetermined using the results from standardpenetration resistance tests (SPT) carried out inaccordance with BS 1377: Part 9. In this case theM* of the existing soil shall be determined fromthe relationship:

M* = 0.39N 1.4

γm

where N = uncorrected SPT value and

γm

= 1.3

5.5 For undrained cohesive soils, M* may bedetermined by measuring the coefficient of volumecompressibility, m

v, in accordance with BS 1377

Part 5 and using the formula:

M* = 1 m

v

The in-situ effective overburden pressure at thelevel of the crown of the structure shall be used inthe test.

5.6 The M* value for design shall then beobtained from Table 5.1 based on the in-situ testresult and also taking into consideration theexcavation width, and the compaction required inMCHW1.

5.7 For structures constructed in embankments,the M* value for design shall be obtained fromTable 5.1 taking into account the compactionrequired.

5.8 When the Contractor proposes a value ofM* for design, in excess of 33N/mm², theContractor shall substantiate the proposed value bytesting the backfill during the back - fillingoperation, using the method given in Clause 642MCHW 1 for plate load testing.

Chapter 5Strength Parameters

5/1

___ (1 - ν2) B ___ Id (N/mm2)π

4

∆q

∆s


November 2001

CLOSED INVERT STRUCTURES

Partial or Total Trench

Constrained Soil Required Required Compaction M* ValueModulus (M*) of Excavation Width for Backfill for Design Use

Existing Soil † on each side of Materials ‡ (N/mm²)(N/mm²) structure

< 15 Span 85% max dry density 20

Span 90% max dry density 33 - 80++

≥ 15 but ≤ 33 Minimum + 90% max dry density As existing soil


> 33 Minimum + 90% max dry density 33


Embankment

- - 85% max dry density 20

- - 90% max dry density 33 - 80++

CIRCULAR ARCH STRUCTURES

Partial or Total Trench

Constrained Soil Required Required Compaction M* ValueModulus (M*) of Excavation Width for Backfill for Design Use

Existing Soil † on each side of Materials ‡ (N/mm²)(N/mm²) structure

≤ 33 Span 90% max dry density 33 - 80++

> 33 Minimum ⊕ 90% max dry density 33


Embankment

- - 90% max dry density 33 - 80++

† Obtained from in-situ test + See Clause 9.8

‡ To be determined from BS 1377 Part 4, ⊕ See Clause 9.9using the vibrating hammer method. ++ See Clause 5.8

Table 5.1 - Design Values of Constrained Soil Modulus (M*)


5/2


November 2001

Nominal Buckling Stress

5.9 The method for determining nominalallowable buckling stress (f

c) is based on the work

of G G Meyerhof (Meyerhof and Baikie, 1963). Anadjustment to the theoretical transverse elasticbuckling stress (f

b) is made to allow for

imperfections of the pipe wall. (fy) is the minimum

yield strength of the steel.

5.10 The nominal allowable buckling stress fc

shall be determined from the following formulae:

ff

1f

f

cy

y

b

=+

where fb = Theoretical transverse elastic buckling

stress (N/mm²) to be taken as follows:

a. When the depth of cover above the crown ofthe structure is greater than or equal to thespan of the structure

( )

f2

a

kEI

1 mprovided

1000S

EI

1 m k

4ba

a2

0.5

a2

0.25=−

−

>

b. When the depth of cover above the crown ofthe structure is less than the span of thestructure

( )( )

f2

a

k EI h

1 m Sprovided

1000S

EI h

1 m k S

4ba

e a2

0.5

a2

e

0.25

=−

−

>

where k = Coefficient of soil reaction (N/mm³)

= 0.333M*_ for circular structures 1000r

= 0.333M*_ for multi-radii structures 1000r

t

and ke

= Modified coefficient of soil reaction(N/mm³)

=

=

E = Modulus of Elasticity of steel= 205 x 103 N/mm²

Ia

= Adjusted cross-sectional moment ofinertia per unit length (mm4/mm) ofthe corrugated steel sheet about itsneutral axis, the section being parallelto the length of structure. (Refer toadjustments required in Clauses 6.1and 7.1) If the cross-sectional momentof inertia varies along the length ofthe structure, the minimum shall beused. The re-rolled ends of helicallywound culvert lengths shall not beconsidered to affect the value of I tobe used unless they extend for morethan 250mm at the end of each length.The effect of the helix angle ofhelically wound culverts on I

a may be

neglected.

h = Nominal height (m) of fill above thestructure (as defined in Clause 3.2)

aa

= Adjusted cross-sectional area ofcorrugated steel per unit length(mm²/mm) (as defined in Clause 4.2)

m = Poisson’s ratio of steel = 0.3.

M* = Constrained soil modulus designvalue (N/mm²) as determined from therequirements of Clauses 5.1 to 5.8.

r = Radius of circular structure (m)

rt

= Radius at the top of multi-radiistructure (m)

S = Span of the structure (diameter ofcircular structure) (m)


5/3

for closed circularand circular archstructures

1r

r h k,

2

−+

for closed multi-radii structures

1r

r h k,t

t

2

−+


November 2001

6. ULTIMATE LIMIT STATE REQUIREMENTS

6.1 The design shall be based on adjustedsectional properties and adjusted nominal seamstrengths based on the residual metal thicknessafter deduction of the appropriate thickness ofsacrificial metal loss, as determined in Chapter 8.

6.2 At the ultimate limit state, the compressivehoop stress, f

a, shall not exceed any of the

following:

a. The nominal allowable buckling stress, fc,

divided by γm = 1.3 where f

c is given in

Clause 5.10.

b. The minimum yield strength, fy, of the steel

divided by γm = 1.3. The value of f

y will be

that nominated and guaranteed by themanufacturer for inclusion in the TypeApproval Certificate for the products. (SeeAnnex A, Clause A.2.3.)

c. In the case of a bolted segmental structure,the stress, f

s, derived from the adjusted

nominal seam strength (as required inClause 6.1), of the longitudinal bolted joint,divided by γ

m of 2.0. The nominal seam

strength shall be as obtained from testscarried out in accordance with Annex B,normally provided by the proprietarymanufacturers for standard metalthicknesses. Adjusted seam strength forintermediate values of residual metalthickness may normally be derived by linearinterpolation between values provided forthe greater and lesser values of metalthickness (in increments no greater than0.75mm), and for the appropriate number ofbolts.

d. In the case of a helically wound structure, astress of 370 N/mm² divided by γ

m of 2.0.

Chapter 6Ultimate Limit State Requirements

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May 2002

7. SERVICEABILITY LIMIT STATE REQUIREMENTS

Deflection

7.1 The design shall be based on adjustedsectional properties which allow for the loss of theappropriate thickness of sacrificial metal loss asdetermined in Chapter 8.

7.2 At the serviceability limit state, the increasein the horizontal diameter or span(S) of thestructure, ∆

x, determined using the following

formula, shall not exceed 5%.

∆x

= _____________________ (m)

where Pd

= Design vertical superimposed deadload pressure at the serviceabilitylimit state (kN/m²)

PL

= Design vertical live load pressureat the serviceability limit state(kN/m²)

K = 1.4, where PL is derived from

wheel loads which, at the level ofthe crown of the structure, have atotal distributed width less than thespan (see Clause 3.5)

or K = 1.0, for all other cases

M* = Constrained soil modulus designvalue (N/mm²) as determined fromthe requirements of Clauses 5.1 to5.8

S = Span of the structure (diameter ofcircular structure) (m).

and E and Ia are as defined in Clause 5.10. S is

defined in Clause 4.2.

Allowable Net Bearing Pressure of theFoundation Material for Closed InvertStructures

7.3 The radial soil pressure, P, for closedcircular structures shall not exceed the allowablenet bearing pressure of the foundation material.The radial corner pressure P

c, for multi - radii

structures, shall not exceed the allowable netbearing pressure of the foundation material or 300kN/m², whichever is less. P and P

c are derived

from C (compressive hoop load) calculated fromunfactored nominal loads (see Clause 4.3). Theallowable net bearing pressure of the foundationmaterial shall be taken to be one third of theultimate bearing capacity calculated in accordancewith BS 8004, as implemented by BD 74 (DMRB2.1.8). Definitions of these terms are given in BS8004, Clause 1.2, as implemented by BD 74(DMRB 2.1.8).

7.4 Where the radial corner pressure Pc exceeds

the lesser of 300kN/m² or the allowable net bearingpressure, consideration shall be given to deepeningand/or widening the trench in accordance withClause 9.2. Account may be taken of the reductionin the value of maximum radial soil pressure withdistance from the face of the structure within thebedding material. The reduced pressure may becalculated as P

c times the radius of the corner

plates, divided by minimum distance from thecentre of radius of the corner plates to the edge ofthe fill. In any event the radial corner pressure P

c in

contact with selected bedding or fill material shallnot exceed 400kN/m².

7.5 Circular Arches - Foundation Design

Foundations shall be in accordance withBS 8004, as implemented by BD 74 (DMRB2.1.8). The bearing pressures generated beneaththe foundation shall be calculated for the loadingsgiven in Clause 4.4. The allowable net bearingpressure shall be taken to be one third of theultimate bearing capacity calculated in accordancewith BS 8004, as implemented by BD 74 (DMRB2.1.8) (see Clause 7.3 above). The maximumbearing pressure shall not exceed the allowable netbearing pressure. Overturning and sliding shall bein accordance with BS 8002 “Earth RetainingStructures”. Guidance is also found in “BridgeFoundations and Sub-structures” (BuildingResearch Establishment 1979).

Checks shall be carried out to ensure the abovecriteria are met when the structure is not subjectedto live loading.

0.083 (Pd + KP

L) S4 x 106

8EIa + (0.02M*S3 x 109)

Chapter 7Serviceability Limit State Requirements

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May 2002

Footings should not be supported on piledfoundations or otherwise constructed in such amanner that differential settlement would occurbetween the structure and adjacent embankment,thereby placing additional loading on the structure.

The design of the reinforced concrete foundationshall be in accordance with BS 5400: Part 4 asimplemented by BD 24 (DMRB 1.3.1) Thedetailed design shall be such as to ensure adequacyof connection between the corrugated steel platesand the foundation both during construction and inservice (see also Clause 10.6).

Reference shall also be made to Clause 8.17 and8.18 for additional requirements

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November 2001

8. DURABILITY

General and Definitions

8.1 The design life of corrugated steel buriedstructures shall be 120 years.

8.2 All surfaces shall be protected by a hot-dipgalvanised coating to BS EN ISO 1461: 1999 usinga minimum average coating weight in accordancewith BS EN ISO 1461: 1999 Table 2. Prior togalvanising, all the structural steel plates shall befully fabricated, ie cut to size, corrugated, curved,and the bolt holes punched or drilled. Theexception to this is the raw edge incorporated intothe folded lockseam as part of the manufacturingprocess of helically wound pipe (formed from pre-galvanised strip to BS EN 10142: 2000). Wheresite cutting is unavoidable, any exposed edge mustbe protected with a cold applied zinc rich paintprior to the application of a secondary protectivecoating.

Helically wound pipe may be formed fromelectrolytically galvanised steel strip precoatedwith a suitable secondary protective coating priorto corrugating, curving and crimping. Thissecondary coating must survive the productionprocess intact and be fully incorporated into thecrimp seam. Such a manufacturing system shallhave a current British Board of Agrément (BBA),Roads and Bridges Certificate, or equivalent.

8.3 Secondary protective coatings shall beapplied to all galvanised steel surfaces. Theminimum requirement for a secondary protectivecoating applied to galvanised steel surfaces shallbe a bituminous coating as defined in BD 35(DMRB 2.4.1) and applied in accordance with thatStandard. Protective coatings intended to providethe minimum requirement shall have a currentHighways Agency registration in accordance withthe procedures described in BA 27 (DMRB 2.4.2).It is not intended that the life of this minimumsecondary protective coating shall be taken intoaccount when calculating the required sacrificialsteel thickness in accordance with clauses 8.10 to8.13. Where it is intended that the life of asecondary protective coating shall be taken intoaccount to reduce the required sacrificial steelthickness, that secondary protective coating shall

have a current British Board of Agrément (BBA),Roads and Bridges Certificate, or equivalent,certifying its life before it requires majormaintenance. The minimum life of a certifiedsecondary protective coating under serviceconditions shall be 20 years before it requiresmajor maintenance.

Measures to achieve Design Life

8.4 Secondary protective coatings may beapplied to galvanised surfaces either in the factory,or on site during construction. The method ofapplication of the secondary protective coatingshall be as described in BD 35 or in the currentBritish Board of Agrément (BBA), Roads andBridges certificate, or equivalent. To reducedamage en route to site the manufacturer shallrecommend methods for transport and handling ofthe coated components and structures. A suitablemethod shall be identified for the repair andpatching of damage to coatings caused duringtransport and construction, and also for makinggood any deterioration in service.

8.5 In selecting the type of secondary protectivecoatings to be applied to the basic galvanised steelstructure the designer shall take into account notonly the environment into which the structure is tobe placed but also the effect on the coating of (i)the span of the structure (the greater the span thegreater the environmental exposure of the interiorcoatings), (ii) its location, and (iii) its accessibilityfor future maintenance.

8.6 Galvanised steel surfaces shall be deemed tocorrode at the rates of corrosion given in Clauses8.11 and 8.13.

8.7 Each surface of the structure shall beprovided with a sacrificial thickness of steel toachieve the required 120 year design life, takinginto account the corrosivity of the environment,contributions from galvanising and contributionsfrom secondary protective coatings with a currentBritish Board of Agrément (BBA), Roads andBridges Certificate or equivalent.

Chapter 8Durability

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November 2001

Corrosivity Classification of Surfaces

8.8 Buried Surfaces

8.8.1 Buried surfaces shall be classified in theSchedule of Employer’s Requirements, eitheraccording to the properties of the surrounding soilor of the effluent water carried, or of the groundwater where present, as determined from theground investigation where applicable. Theclassification shall be the most severe of the three.It should be appreciated that effluent water and/orgroundwater can penetrate through bolt holes andseams to affect equally both internal and externalsurfaces of the culvert. The selected fills, Classes6K, 6L and 6M described in MCHW1 Clause 623,shall provide a non aggressive environment whendry and used to replace soils within the zoneindicated in Clause 8.8.3, but any water presentwill determine the classification based on itsproperties. Refer also to Clause 14.3.

8.8.2 The surrounding soil, invert fill, silt depositsand select fill types in Clause 8.8.1 shall beclassified using the points system for eachproperty, shown in Table 8.1, and the ground watershall be classified according to the highestaggressivity indicated for any property inTable 8.3. The properties shall be assessed usingthe test methods listed in Table 8.2. Additionally,where the culvert carries a continuous flow ofwater or other fluid, classification of the water/other fluid according to Table 8.3 shall be used toclassify both surfaces if it is more severe than theclassification of the surrounding soil or groundwater.

y = 0.4 + 0.23S

where S = span of the structureand both S and y are in metres

Figure 8.1 - Corrosivity Classification Zonefor the External Buried Surface

Chapter 8Durability

8/2

8.8.3 For structures constructed partly or totally intrench, the existing soil within the zone shown inFigure 8.1 shall be tested for corrosivityclassification purposes.

8.8.4 The inner surface of the structure shall beregarded as a buried surface beneath any part thatis to be covered eg when a structure is used as avehicular underpass or has invert protection. Anywater or fill present shall be used to determinecorrosivity classification as in Clauses 8.8.1 and8.8.2. Both inner and outer surfaces beneath thiscovered part shall be classified for aggressiveconditions if it is likely that road salt or otherchemicals in solution will come into contact withthem from whatever source. Refer also to Clause14.3.

8.9 Exposed Surfaces

8.9.1 Exposed surfaces shall be classified in theSchedule of Employer’s Requirements accordingto the aggressivity of any water or other fluidcarried by the structure or the aggressivity of theground water (to allow for water percolationthrough joints or bolt holes) using the criteria inTable 8.3, and also according to the corrosivity ofthe atmosphere using the criteria in Table 8.4. Theoverall classification shall be determined by themost severe of the three.

8.9.2 Consideration shall be given to the effect onexposed surfaces of the presence of chloride ionsfrom road salt. It has been found that chloride canpersist in the water carried throughout the yearincluding the summer months and may percolatethrough joints or bolt holes.

8.9.3 The harshness of the atmosphericenvironment shall be determined by the DesignOrganisation from the map “Relative Values ofAcid Deposition in the United Kingdom 1986 -1991” published by ADAS, Reading (3). Thecorrosivity (acid deposition) value shall be takenas the average of the values indicated by the chartgrid square in which the proposed structure is sitedand the three nearest adjoining squares. Theatmospheric environment for the exposed surfacesshall be determined from this corrosivity valueusing Table 8.4. However, any other significantenvironmental factors concerning the location shallalso be taken into account eg wind blown saltspray near the coast or pollution from a nearbyindustrial plant may override the general


February 2002

classification, or constitute a very aggressiveenvironment.

Life of Protective Coatings and Sacrificial SteelThickness for All Surfaces

8.10 The design life of the structure shall be thesum of the life of the sacrificial steel, the life of thegalvanised coating and the life of the secondaryprotective coating.

8.11 The life of the galvanised coating shall becalculated from the rate of corrosion which shallbe taken as 4µm/year in non-aggressiveenvironments and 14µm/year in aggressiveenvironments. Galvanising thickness may beassumed to be 1µm for each 7.15 g/m² coatingweight.

8.12 The life of a secondary protective coatingapplied to the galvanised steel components shall beas determined in the current British Board ofAgrément (BBA), Roads and Bridges Certificate orequivalent for the coating used.

8.13 The sacrificial thickness of steel required toprovide 120 years life less the life of the coatings,shall be calculated from the formulae:

T = 22.5t 0.67, for non-aggressiveenvironments; and

T = 40.0t 0.80, for aggressiveenvironments,

where T = thickness of sacrificial steel oneach surface (µm),

t = life of sacrificial thickness of steelin years.

Invert Protection

8.14 In addition to the requirements of Clauses8.10 to 8.13, the invert of all structures carryingwater or other fluid shall be protected from theeffects of abrasion or erosion by adopting one ofthe following protection systems:

a. A reinforced concrete paving (See Clauses13.1 to 13.7) with a minimum thickness of100mm for structures of span less than orequal to 2m, and with a minimum thicknessof 125mm for all other structures.

b. As an alternative to a reinforced concretepavement the following may be used for allspans and gradients:

i. Paving blocks of 60mm minimumthickness bedded on a compactedType 1 sand bed, with concreteflaunchings used at the edges toprovide a transition between thepaviours and the sides of the CSBS.

ii. Precast slabs or natural stone set intomass concrete having a minimumthickness of 300mm. The pavementmay be profiled to suit localrequirements, for example theinclusion of a channel to retain waterunder low flow conditions; shaping tosimulate a natural channel; and theprovision of animal runs. Weirs oreddy pools may be included withinthe structure to provide resting placesfor fish etc. passing through thestructure. Upstanding stone set intothe concrete may also be used for thispurpose.

iii. A liner plate manufactured from, forexample, galvanised steel sheet orglass reinforced plastic (GRP) andpre-shaped to the profile of the invert,may be secured to the CSBS. Thevoid between the liner plate and theinvert shall be filled with acementitious grout or other waterresistant material.

c. A proprietary system giving an equivalentlevel of invert protection and certified assuitable for the end-use by the British Boardof Agrément or equivalent body, who willalso certify its design life.

d. For structures with little or no flow, andwhich are therefore likely to hold standingwater, the following may be used asalternatives to pavements:

i. A coating certified as suitable for theend use by a current British Board ofAgrément, Roads and BridgesCertificate, or equivalent, may beused. The design life shall be statedon the certificate.

Chapter 8Durability

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February 2002

ii. The use of liner plates secured to thestructure to cover fluctuations of atleast 200mm above and below therange of water depths. The liner platesmay be formed from, for example,galvanized steel strip coated with abitumen-based product (or othersuitable protective coating) or fromGRP. The plates may be shaped tofollow the curvature of the walls ofthe structure and if required may be ofsufficient size to completely cover theinvert. Any gap between the liner andthe structural shell should be filledwith, for example, concrete orcementitious grout or other waterresistant filler, to seal the interiorsurface of the structure. The linerplates may be provided with groutingpoints to facilitate the filling of thevoid. If a secondary protective coatingis used to protect galvanised steelliner plates, its design life given in acurrent British Board of Agrément,Roads and Bridges Certificate, orequivalent, may be taken into account.

8.15 Invert protection shall be applied to thewetted periphery of the structure for the winterbase flow plus 200mm on each side or 25% of thetotal circumference for circular structures or 40%of the total circumference for multi-radii structureswhichever is greater. Where the invert protection isin concrete and exceeds 25% of the totalcircumference for circular structures or 40% ofmulti-radii structures, or as appropriate for acircular arch structure, formwork shall be used inits installation. Any gap between the pavement andthe structural plates shall be sealed with anappropriate sealant. The point at which thepavement meets the structural plates shall beshaped to prevent ponding of water against thestructural plates. To prevent accelerateddifferential corrosion of the steel culvert,particularly at the wet/dry line, paved inverts mustbe inspected at regular intervals whenmaintenance/replacement shall be carried out asappropriate.

8.16 Subject to the agreement of the appropriateriver authority or Environment Agency, screensshall be installed at the inlet of a culvert when it is

anticipated that water-borne stones or other debrisin excess of 100mm diameter would otherwise becarried through it during normal or floodconditions. For a culvert installed with a gradientgreater than 2 per cent, it is desirable to removewater-borne stones or fragments of less than100mm diameter through installation of drop inletsor catchpits.

Invert Protection Below Circular Arch Structures

8.17 Reinforced concrete invert paving asdescribed in the relevant parts of Clause 8.14 shallbe provided, where necessary, to protect the archfoundations and foundation material from scour,abrasion or chemical attack from flowing water orother fluid if present. The design of the pavingshall take account of hydraulic factors, thefoundation material and the nature of the stream/river bed.

8.18 Where the level of winter flow is above thefoundation level, the invert paving shall also beapplied to the corrugated steel as described inClause 8.15. The most vulnerable area of an archstructure to deterioration is at the springing andgreat care shall be taken to avoid water entrapmentat this point. A typical detail is shown in Figure8.2. The detail adopted should avoid entrapment ofwater on the soil side of the structure and, whereconcrete upstands are used, against the inside ofthe arch structure: any gap between the structuralplates and the pavement must be thoroughly filledand waterproofed. This seal shall be designed to bemaintainable. Care shall be taken to ensure thatany of the work done to protect the CSBS will notadversely affect its structural performance.

8.19 Impact Protection

a. In the case of structures to be used byvehicles consideration shall be given toprotecting the sides of the structure bykerbing and/or by means of an appropriatevehicle restraint system which should not beconnected to the sides of the structure.Advice on a suitable system may beobtained from the Overseeing Organisation.Some measure of protection to the crown/soffit should be provided by suitable designof headwalls or ring beams and by alertingdrivers to the headroom restriction by meansof visual and/or audible warning systems.

Chapter 8Durability

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November 2001

b. Where water carrying structures are to beused by water craft, adequate protectionagainst impact and abrasion shall beincorporated in the form of rubbing boardsetc. Suitable provision shall be made formaintaining and replacing such items asnecessary.

8.20 Reinforced Concrete Foundations

The Overseeing Organisation’s requirements forreinforced concrete are contained in Series 1700 ofMCHW1. The concrete mix shall be Grade 30 orhigher. Further guidance is given in Series NG1700of Notes for Guidance on the Specification forHighway Works MCHW2. Detailed guidance onthe assessment of ground aggressivity to concreteis given in Part 1 of BRE Special Digest SD1“Concrete in aggressive ground” (2001). Theground to be assessed should include thesurrounding ground, the groundwater, the generalembankment fill and the backfill material, and anycontained water or effluent to be carried by thestructure. It should be noted that the groundproperties to be assessed and classificationprocedure in respect of concrete are different tothose recommended for steel structures in Tables8.1, 8.2 and 8.3 of this Standard. Detailed guidanceon the specification of concrete for foundations inaggressive ground is given in parts 2 and 3 of BRESpecial Digest SD1. Provision is made in theDigest for the use of various cement and cementcombinations in conjunction with aggregates ofdiffering carbonate content. The Digest alsorecommends additional protective measures forconcrete where ground water is mobile and sulfateconcentrations are high.

Chapter 8Durability

8/5


November 2001

PROPERTY MEASURED VALUE POINTS

Fraction passing 63µm sieve ≤ 10%Plasticity Index (PI) of fraction + 1passing 425µm sieve ≤ 6

Fraction passing 63µm sieve > 10%PI of fraction passing 425µm sieve ≤ 6 0

Soil Type Any gradingPI of fraction passing 425µm sieve > 6 but < 15 - 1

Any gradingPI of fraction passing 425µm sieve ≥ 15 - 2

Organic matter > 1.0%or material containing peat, cinder or coke - 3

≥ 10,000 + 2< 10,000 but ≥ 3,000 + 1

Resistivity < 3,000 but ≥ 1,000 - 1(ohm - cm) < 1,000 but ≥ 100 - 3

< 100 - 4

pH of soil 6 ≤ pH ≤ 9 05 ≤ pH < 6 - 2Less than 5 or more than 9 - 4

Water-soluble ≤ 0.24 0sulfates (WS) > 0.240 but ≤ 0.60 - 1(g/l as SO

4) > 0.60 but ≤ 1.20 - 2

> 1.20 - 4

Chloride ion ≤ 50 0(ppm) > 50 but ≤ 250 - 1

> 250 but ≤ 500 - 2> 500 - 4

Oxidisable ≤ 0.05 0sulfides (OS) > 0.05 but ≤ 0.12 - 1(% as SO

4) > 0.12 but ≤ 0.24 - 2

> 0.24 - 4

POINTS TOTAL CORROSIVITY CLASSIFICATION

0 or more Non aggressive- 1 to - 4 Aggressive- 5 or less Very aggressive

Table 8.1 Corrosivity Classification of Surrounding Soil

Chapter 8Durability

8/6


November 2001

PROPERTY TEST METHOD

Soil Type:

Grading BS 1377 : Part 2Plasticity Index (PI) BS 1377 : Part 2Organic Matter BS 1377 : Part 3

Resistivity Clause 637, MCHW1

pH BS 1377 : Part 3

Water-soluble sulfate and oxidisable sulfides TRL Report 447 Test Nos 1, 2 and 4

Chloride ion content BS 812 : Part 117

Table 8.2 - Test Methods for properties required in Table 8.1 and Table 8.3

NOTES (TABLES 8.1 AND 8.2)

1. When sampling for organic matter determination, great care must be taken to avoid contamination with topsoil, roots or overlying made ground. If contamination cannot be avoided, reduce the number of negative pointsawarded in Table 8.1.

PROPERTIES OF WATER OR EFFLUENT

CORROSIVITYCLASSIFICATION pH Chloride ion Water-soluble

(ppm) Sulfate (WS)(g/l as SO4)

Non-Aggressive 6 ≤ pH ≤ 9 ≤ 50 ≤ 0.24

Aggressive 5 ≤ pH < 6 > 50 but ≤ 250 > 0.24 but ≤ 0.60

Very Aggressive Less than5 or more > 250 > 0.60

than 9

Table 8.3 - Corrosivity classification of ground water, carried water and other contained fluids

Average Corrosivity Value Classification of the(Acid Deposition Value from Atmospheric Environment

ADAS map)

≤ 2 Non-Aggressive> 2 but ≤ 4 Aggressive

> 4 Very Aggressive

Table 8.4 - Classification of Surfaces Exposed to the Atmospheric Environment

Chapter 8Durability

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November 2001

Chapter 8Durability

8/8


November 2001

9. EXCAVATION AND FILLING

Excavation for Bedding of Closed Invert Structures

9.1 Excavation for the bedding of closed invertcorrugated steel buried structures shall extend to adepth below invert level of not less than one tenthof the span and to a width not less than 800mm(500mm for structures up to 3m span) beyond thespan on each side, provided that the allowable netbearing pressure at this depth exceeds themaximum radial soil pressure (P or P

c). In any

event the excavation width should be not less thanthe extent of side fill required in Table 5.1. Theexcavation shall extend a length not less than300mm beyond each end of the structure (seeFigures 9.1 and 9.2).

9.2 Where the allowable net bearing pressure ofthe foundation material at the excavation levelgiven above is less than the maximum radial soilpressure (P or P

c), the excavation shall be

continued to such a depth that the allowable netbearing pressure at the new excavation level is notless than the maximum radial soil pressure.Account may be taken of the reduction in the valueof maximum radial soil pressure with distancefrom the face of the structure as described inClause 7.4. The allowable net bearing pressure ofthe bedding material must not be exceeded. Whenadditional excavation is necessary it shall be widerthan the limits given in Clause 9.1 by an amounton each side equal to the extra depth (see Figures9.1 and 9.2).

9.3 Excavation in hard material shall extend toan additional depth of not less than 300mm belowthe level indicated in Clause 9.1 plus 40mm foreach metre of cover, in excess of 8m, above thecrown of the completed structure up to a maximumadditional depth of 600mm.

Excavation of the Foundation Level for CircularArches

9.4 The excavation for the foundation level shallextend to a width not less than 800mm (500mm forcircular arches up to a 3m span) beyond the spanon each side and in any event to be not less thanthe extent of side fill required in Table 5.1.

9.5 Additional excavation may be necessary to suitthe foundation size selected and the working spacerequired for construction of the foundation andbackfilling the structure.

9.6 In cases where the net allowable bearing pressureof the foundation material at an excavation level resultsin an impractical size of foundation, as calculated inaccordance with Clause 7.5, the excavation level maybe continued to such a depth to locate an improved netallowable bearing pressure of the foundation material.The additional excavation can be replaced with suitablefoundation material as indicated on Figures 9.1 and 9.2.Alternatively, the depth of the foundation may beincreased. In both cases the foundations shall bedesigned in accordance with Clause 7.5.

9.7 The depth of excavation to the foundationlevel is measured from the top of the foundationand is defined as (1000+D)mm (see Figures 9.1and 9.2). In such a case, the width of excavation atthe foundation level shall be (500+D)mm forcircular arches up to 3m span and (800+D)mm forcircular arches of span 3m or greater, beyond thespan on each side (see Figures 9.1 and 9.2).

Trench Width for Closed Invert Structures

9.8 The trench width shall be not less than threetimes the span (S) of the structure, unless theconstrained soil modulus (M*) of the existing soilis greater than the values adopted for design (seeTable 5.1) when the trench width may be reducedto the minimum required for the lower beddingmaterial, that is normally the span plus 500mmeach side for structures up to 3m span, or span plus800mm each side for larger spans, or as otherwiserequired in Clause 9.2 and shown in Figure 9.1. Apartial trench condition occurs when the level ofexisting soil suitable for retention within a distanceof a span either side of the structure lies betweenthe crown of the structure and the underside of thelower bedding. Refer to Figure 9.1. Partial trenchescan be treated similarly to trenches; alternativelythe excavation shall extend to a distance equal tothe span on each side of the structure. Reference toClause 8.8.3 is also necessary.

Chapter 9Excavation and Filling

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November 2001

Trench Width for Circular Arches

9.9 The trench width shall be not less than threetimes the span (S) of the structure, unless theconstrained soil modulus (M*) of the existing soil,within this extent, is greater than or equal to thevalues adopted for design (see Table 5.1), when thetrench width may be reduced to the minimumrequired for the width of excavation specified inClause 9.7 and shown in Figure 9.1. A partialtrench condition occurs when the level of existingsoil suitable for retention within a distance of aspan either side of the structure lies between thecrown of the structure and the underside of thelower bedding. Refer to Figure 9.2. Partial trenchescan be treated similarly to trenches; alternativelythe excavation shall extend to a distance equal tothe span on each side of the structure. Reference toClauses 8.8.3, 9.4 and 9.7 is also necessary.

Filling - General

9.10 The earthworks requirements for theselected fills and their compaction requirementsare given in Series 600 MCHW1.

Filling - Bedding for Closed Invert Structures

9.11 As far as possible, the lower beddingmaterial (Class 6K in Table 6/1 MCHW1) shall beshaped to fit the invert such that it supports 20% ofthe circumference of circular structures or thewhole of the portion of cross section of radius r

b(see Table 1.1) for multi-radii structures. If thiscannot be met and the structure is erected on flat orpartially preshaped bedding, care must be taken toensure that the lower bedding material is properlyplaced and compacted under the haunches.

9.12 The upper bedding material (Class 6L inTable 6/1 MCHW1) is as described in Series 600MCHW1.

Filling - Surround for All Structure Types

9.13 The surround material (Class 6M in Table6/1 MCHW1) as described in Series 600 MCHW1shall be used for filling all excavations, exceptthose in hard material for which lower beddingmaterial (Class 6K) shall be used, with minimumexcavation. In all cases (for embankments andtrenches and partial trenches) surround fill shall

extend to a height of not less than a fifth of thespan or 650mm whichever is the greater, above thecrown of the structure, or to the formation level ofthe road if this is lower. See Clause 9.16 forrequirement for placing of fill.

9.14 In embankments the surround material shallbe used for a minimum distance equal to the spanon each side of the structure. In trenches thesurround material shall be used for a minimumdistance as defined in Clause 9.8 or 9.9 on eachside of the structure. For partial trenches (wherethe level of the existing ground suitable forretention is lower than the crown of the structure)the surround material in the trench may be used fora minimum distance as defined in Clause 9.8 or9.9. Alternatively, the fill shall extend to a distanceequal to the span of each side of the structure. Thesurround material above the level of the existingsoil suitable for retention in partial trenchconditions shall be used for a minimum distanceequal to the span on each side of the structure. (SeeFigures 9.1 and 9.2.)

Filling - Overlying Fill above All Structural Types

9.15 The overlying fill material as described inMCHW1 Series 600 shall be used for embankmentconstruction in the zone over the structure shownin Figures 9.1 and 9.2. Argillaceous rocks such asshales and mudstones, slag and PFA shall not beused as fill or road sub-base materials in this zone.

Filling - Deposition, Spreading and Compaction

9.16 Surround fill and fill placed above the levelof the crown of the structure, as described inClause 9.13 to 9.15, shall be deposited, spread andcompacted in such a manner that any out ofbalance forces transmitted to the culvert are kept toa minimum. This will require that trafficking byconstruction plant is not all in one direction andthat the compacted surface of the fill is kept asnear horizontal as practicable.

9.17 Compaction of the surround material shallcomply with the requirements given in Series 600MCHW1 except that in some circumstances it maybe more economical to relax the requirement to85% of the maximum dry density. (See Table 5.1.)


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9/4

level

level


November 2001

10. HANDLING AND INSTALLATION

10.1 Structures must have enough rigidity topermit practical handling and installation. For thispurpose a flexibility factor, F shall be calculatedfrom the formula:

F = S² x 106

EI

where S = Span of the structure (m)E = Modulus of Elasticity of steel

= 205 x 10³ N/mm²I = Cross-sectional Moment of inertia

per unit length, (mm4/mm) of thecorrugated steel sheet about itsneutral axis, the section beingparallel to the length of thestructure. If the cross sectionalmoment of inertia varies along thelength of the structure, theminimum shall be used. There-rolled ends of helically woundculvert lengths shall not beconsidered to affect the value of Ito be used unless they extend formore than 250mm at the end ofeach length. The effect of the helixangle of helically wound culvertson I may be neglected.

10.2 For acceptable performance duringinstallation, the flexibility factor, (F) must be lessthan a limiting value (F

max), which depends on the

depth of corrugation (dc). For the purposes of this

Clause the depth of corrugation (dc) is defined as

the depth in millimetres from any peak to theadjacent trough in the corrugation.

10.3 For circular structures, circular arches and

multi-radii structures with 1.3 > r

rc

t> 0.7 where

rc is the corner radius and r

t is the top radius, the

value of Fmax

shall be calculated from the formula:

Fmax

= 0.29 – 0.0034 dc

but with a minimum of 0.115mm/N and amaximum of 0.25mm/N. d

c is defined in Clause

10.2.

10.4 For multi-radii structures with 0.7 > r

rc

t> 0.2,

as defined in Clause 10.3 the value of Fmax

shall becalculated from the formula:

Fmax

= 0.435 – 0.0051 dc

but with a minimum of 0.173mm/N and amaximum of 0.375mm/N. d

c is defined in Clause

10.2.

10.5 If F ≤ Fmax

the structure is acceptable. In thecase where F

max < F the structure is not acceptable

and either the span S must be reduced, the flexuralrigidity EI must be increased or temporarysupports must be used. If temporary supports areused (Clause 3.1b) then a temporary works designis required to ensure local overstressing anddistortion of the corrugated steel is avoided. Partialsafety factors in Clause 3.10 (Table 3.1) shall beused in conjunction with appropriate values of γ

f3(Table 4.1).

Foundations for Circular Arches

10.6 The connection between the corrugated steelplates and the reinforced concrete foundation isnormally achieved using a seating channel suppliedby the manufacturer. The seating channel shall becapable of transmitting loads from the corrugatedsteel plates into the foundation both duringconstruction of the structures and in service.Reference shall be made to the requirements ofClause 7.5.

Chapter 10Handling and Installation

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11. END TREATMENT

11.1 End treatments shall be included within thedesignated outline as defined in SD4 (MCHW0.2.4). All end treatments shall be designed inaccordance with Clauses 11.2 to 11.6 and regardshall be paid to the aesthetic appearance of thestructure.

11.2 Reinforced concrete collars, headwalls, orretaining walls shall be designed to support theface edges of the corrugated steel where the skewangle of the corrugated steel structure exceeds 15°,the bevel of square ends exceeds 2:1 (egembankment flatter than 1 in 2), or the cut endsupports highway loading. In these instances thereinforced concrete elements shall be designed tooffer adequate support to the corrugated steel shellwhere it is discontinuous and unable to act in ringcompression normal to the centre line of thecorrugated steel structure. The structural adequacyof the corrugated steel plates is to be considered.Structural steel ring beams, collars, and spreaderbeams may be utilised, together with ties anchoredinto the fill, and shall be designed to theappropriate Standards. Reinforced concreteelements shall be designed according to BS 5400:Part 4 as implemented by BD 24 (DMRB 1.3.1).Account shall be taken of the effects of theconstruction sequence, loads from the corrugatedsteel plates being directly supported, other loadsfrom the corrugated steel structure, the self weightof the reinforced concrete, earth pressures, theeffects of ground creep and settlement, andhydraulic loadings. Partial safety factors in Tables3.1 and 4.1 shall be adopted as appropriate. Iftemporary works are necessary the requirements ofClause 10.5 shall be adopted.

11.3 In other instances the backfill and free edgesof other corrugated structures shall normally beprotected by end treatments such as headwalls orcollars. The loading considerations for the designof the end treatment shall be the same as thoserequired in Clause 11.2.

11.4 Consideration should be given to the weightof the wet concrete when forming the headwall,ring beam or collar during construction. In somecircumstances, it may be necessary to installtemporary supports.

11.5 For hydraulic structures, measures shall betaken to secure the metal edges at inlet and outletagainst hydraulic forces.

11.6 In the case of hydraulic structures, theheadwall, ring beam or collar shall be designed totake into account the possible effects of scour ofthe material beneath the invert of the structure.

11.7 The designer shall identify on the Contractdrawings any construction sequence assumed inthe design.

Chapter 11End Treatment

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November 2001

12. OVERLYING REINFORCED CONCRETE SLAB

12.1 Where the depth of cover measured from thefinished road surface to the crown of the structureis less than the greater of span/5 or 650mm (Clause1.3b), a reinforced concrete slab may be usedwithin the thickness of the carriageway pavementabove the corrugated steel culvert or underpasswith a reduced thickness of cover above the crownof the structure. A minimum thickness of 150mmof surround material (Clause 9.13, Class 6M inTable 6/1 MCHW1) shall be placed and compactedbetween the crown of the structure and theunderside of the slab.

12.2 The length of the reinforced concrete slabshall be sufficient to extend beyond each side ofthe structure for a distance of 3 metres or half thespan of the structure which ever is greater.

12.3 Where the carriageway pavement isreinforced concrete, the slab may constitute theconcrete pavement continued over the crown of thestructure. In this case, the thickness of the slab(minimum 200mm) and reinforcement shall be inaccordance with HD 26: Pavement Design (DMRB7.2.3.)

12.4 Alternatively the concrete may form thelower half of a composite pavement, normallyoverlain by 100mm of flexible surfacing. Againthickness and reinforcement shall be in accordancewith HD 26 or with BS 5400: Part 4 asimplemented by BD 24 (DMRB 1.3.1).

12.5 It is important to ensure adequate compaction ofthe fill material under the ends of the slab to prevent theformation of voids leading to the production of dynamicload effects under trafficking.

Chapter 12Overlying Reinforced Concrete Slab

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13. CONCRETE INVERT PAVING FOR CLOSEDINVERT STRUCTURES

13.1 When a concrete invert paving inaccordance with Clause 8.14 is to be used, it shallbe as described in the following Clauses.

13.2 The concrete shall be Class 30/20 asdescribed in MCHW1 Series 1700.

13.3 The concrete invert paving shall bereinforced with a steel fabric complying withMCHW1 Series 1700 having mesh dimensions notgreater than 150mm x 300mm and a nominal wiresize not less than 5mm. All laps in the mesh shallbe at least 150mm. The steel fabric shall besecurely fixed to the structure by means of fixingsat the bolt positions. It shall extend to within adistance not greater than 100mm, nor less than40mm inside the edges of the concrete on eachside. A nominal cover of 45mm shall be providedto all other faces, including that to the crest of thecorrugations in the structural steel.

13.4 The invert shall be cast in lengths notexceeding 10 metres with the provision of a waterbar between adjacent panels and the joints sealedwith a joint sealant to Clause 2303 MCHW 1.

13.5 Prior to commissioning, a flaunch (mortarslope) shall be applied at the plate/pavementinterface to seal gaps and avoid the problem ofstanding water on ledges adjacent to the shell ofthe CSBS.

13.6 At each end of the structure the concreteinvert paving shall be either:

a. Terminated with a toe that returns at least200mm under the structural steel formingthe structure. The steel fabric shall be foldedunder the lips of the structure to suit. Thetoe shall be detailed with a thickness of notless than that required for the paving, asdetermined from Clause 8.14, or

b. Detailed to suit any headwall arrangementeg paving reinforcement lapped withheadwall reinforcement.

13.7 All foreign matter, (but not any secondaryproprietary protective coating unless indicatedotherwise in the Type Approval Certificate orBritish Board of Agrément (BBA), Roads andBridges Certificate referred to in Clause 1.6) andfree standing water shall be removed from thesurfaces to be paved, before commencing work.

Chapter 13Concrete Invert Paving for Closed Invert Structures

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14. CARRIAGEWAY DRAINAGE

14.1 All measures shall be taken to avoidcontaminated carriageway water (impregnated withroad salts) collecting on the buried face of thestructure. In the vicinity of the structure,carriageway drainage shall be constructed withwatertight joints and tested as described in the 500Series MCHW1, and the trenches lined with aheavy-duty impervious membrane prior tobackfilling. Carriageway drainage filter drains(including fin drains), soakaways, and wherepossible, gullies and chambers, shall not be sitednear the structure. A zone bounded by planesprojected at a slope of 1 horizontally to 1 verticallyfrom the extremities in plan of the structure willnormally be sufficient for these requirements.

14.2 Carriageway drainage outfalls shall be siteddownstream of the structure.

14.3 If, exceptionally, the requirements ofClauses 14.1 and 14.2 are not achieved it shall beassumed that contaminated water will affect boththe inner and outer faces of the corrugated steelstructure, giving rise to the surfaces beingclassified for aggressive conditions in accordancewith Clauses 8.8 and 8.9.

Chapter 14Carriageway Drainage

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15. MULTIPLE INSTALLATIONS

15.1 Adjacent structures shall be separatedsufficiently for mechanical equipment to operatebetween them for adequate compaction. In theabsence of special measures, the spacing shall notbe less than:

circular structures i) up to 2m span - onehalf of the span of thelarger structure or600mm whichever isgreater.

ii) 2m to 8m span - 1m.

multi radii structures i) up to 3m span - onethird of the span ofthe larger structure or600mm whichever isgreater.

ii) 3m to 8m span - 1m.

Chapter 15Multiple Installations

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November 2001

16. TECHNICAL REQUIREMENTS AND DESIGNCHECKLIST

16.1 The procedures to be followed when specifying aproprietary manufactured structure are given inStandard SD4 (MCHW 0.2.4). The particularrequirements for corrugated steel buried structures aredescribed here.

16.2 The Design Organisation, prior to invitingtenders, normally submits an Outline Approval inPrinciple containing a Schedule of Employer’sRequirements which should include the followinginformation:

i. Location plan and name of structure.

ii. Environmental considerations (see clause 1.4).

iii. Long Section along centre-line of structure.

iv. Finished levels of carriageways and side slopeswithin designated outline.

v. Skew of structure.

vi. Minimum width of structure.

vii. Minimum headroom of structure.

viii. Hydraulic requirements or clearance envelope, ifany, and requirement for invert protection.

ix. Gradient of invert.

x. End detail requirements, including anyrequirement for reinforced concrete headwalls.

xi. Highway loading requirements.

xii. The value of constrained soil modulus M* to beassumed for existing soil.

xiii. Allowable net bearing pressure for foundationmaterial.

xiv. The corrosivity (aggressivity) classification ofexisting soil, ground water, contained water/effluent, the atmosphere and of any fill material(or silt) to be placed inside the structure incontact with the corrugated steel. A drawing isalso required showing the corrosivity

classification for each surface type on thestructure on a suitably marked up cross section.The extent of each surface type (includingmaintained surfaces) shall be clearly indicated.

xv. Protection of structures against vehicle impact.

xvi. Public safety requirements including lighting andprotection for pedestrians round headwalls.

xvii. Aesthetic requirements including colour ofcoatings.

xviii. Identification of any elements in addition to thecorrugated steel plating requiring design.

xix. Any other essential requirements.

Special requirements should be avoided. Howeverwhere the circumstances are such that they are justifiedthen care must be taken to avoid requirementsimplicitly favouring the system of a particularmanufacturer.

16.3 Subsequent to the award of contract and prior tothe commencement of construction, the Contractornormally completes the AIP form (containing theSchedule of Employer’s Requirements), the design andthe design certificate, and submits these for approval/appraisal. The full design normally contains thefollowing additional information relating to theparticular proprietary product which forms the basis ofthe design. For bolted segmental structures the listincludes:

a. Structure Geometry:

- Structure type/shape

- Internal span

- Internal height

- Radii.

Chapter 16Technical Requirements and Design Checklist

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November 2001

b. Materials:

- Steel specification

- Corrugation dimensions

- Nominal thicknesses of steel andgalvanising

- Additional protective coatings (if any)

- Proprietary secondary protective coatings(if proposed) - thickness and other relevantdetails

- Invert protection system details - concreteor proprietary system.

c. Bolts and Nuts:

- Specification

- Arrangement at joints

- Torque.

d. Footings of Circular Arches (if relevant):

- Geometry

- Concrete type

- Reinforcement

- Allowable net bearing pressure offoundation material

- Means of connecting structure to footing.

e. End Treatment:

- Geometry

- Concrete type and reinforcement(if required)

- Means of connection to structure.

f. Construction sequence.

g. Confirmation of foundation depth and material.

h. Internal fill in contact with wall of structure:

- Soil properties, bulk density, grading andcorrosion classification in accordance withChapter 8.

i. The current Type Approval Certificate andcurrent British Board of Agrément Roads andBridges or equivalent Certificate or Certificates -as required in Clauses 1.6 to 1.9.

And for helically wound pipes:

a. Structural Geometry:

- Internal diameter.

b. Materials:

- Corrugation dimensions

- End corrugation dimensions

- Nominal thicknesses of steel andgalvanising

- Coupling band details

- Proprietary protective coatings (ifproposed) - thickness and other relevantdetails

- Invert protection system details.

c. End Treatment:

- Geometry

- Concrete type and reinforcement (ifrequired)

- Means of connection to structure.

d. Construction sequence.

e. Confirmation of foundation depth and material.

f. Internal fill in contact with wall of structure:

- Soil properties, bulk density, grading andcorrosion classification in accordance withChapter 8.

g. The current Type Approval Certificate andcurrent British Board of Agrément Roads andBridges or equivalent Certificate, as required byClauses 1.6 to 1.9.

16.4 The Contractor shall additionally supply with hisdesign the following information relating to the designrequirements of the earthworks:

Lower Bedding Material:

- Constrained soil modulus (M*).

- Compaction (% of maximum dry density).

- Durability classification to Clause 8.8.2.

Surround Material:

- Constrained soil modulus (M*).

- Compaction (% of maximum dry density).

- Durability classification to Clause 8.8.2.


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November 2001

16.5 The further stages in the post award contractprocedures are given in Chapter 4 of Standard SD 4(MCHW 0.2.4).

16.6 Following construction copies of the followingwill be required for inclusion in the maintenancemanual and health and safety file:

1. The completed AIP used for design.

2. A set of as constructed drawings, including arecord of the final structure profiles achieved.

3. A design summary for information listed inClauses 16.3 and 16.4.

4. Other relevant information.


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November 2001

Chapter 17References

17/1

17. REFERENCES

17.1 Design Manual for Roads and Bridges

Volume 1: Section 1 Approval ProceduresBD 2: Part 1 - Technical Approval of Highway

Structures (DMRB 1.1)Volume 1: Section 3 General DesignBD 24: Design of Concrete Bridges. Use of

BS 5400 Part 4(DMRB 1.3.1).BD 37: Loads for Highway Bridges

(DMRB 1.3)Volume 2: Section 2 SubstructuresBD 74 Part 8 – Foundations (DMRB 2.1.8)Volume 2: Section 4 Paints and other Protective

CoatingsBD 35 Quality Assurance Scheme for Paints

and Similar Protective CoatingsVolume 2: Section 4 Paints and other Protective

CoatingsBA 27 Quality Assurance Scheme for Paints

and Similar Protective CoatingsVolume 7: Section 2 Pavement Design and

ConstructionHD 26: Pavement Design (DMRB 7.2.3)Volume 10: Environmental Design.

17.2 Manual of Contract Documents for HighwayWorks

Volume 0: Section 2 Implementing StandardsSD4 Procedures for Adoption ofProprietary Manufactured Structures(MCHW 0.2.4).Section 3 Advice NotesSA1 Lists of Approved/RegisteredProducts (MCHW 0.3.1)

Volume 1: Specification for Highway WorksHMSO 1998 (MCHW1) with revisionsto 2001

17.3 British Standards

BS 812: Part 117: 1988 - Method forDetermination of Water SolubleChloride Salts. Replaced byBS EN 1744-1:1998 but remainscurrent

BS 1377: 1990 - Methods of Test for Soils forCivil Engineering Purposes.

Part 2: Classification tests.Part 3: Chemical and electro-chemical tests.

Part 4: Compaction-related tests.Part 5: Compressibility, permeability and

durability tests.Part 9: In-situ tests.BS EN ISO 1461 1999. Hot dip galvanised coatings

on fabricated iron and steel articles- Specifications and test methods.

BS EN 1744 Tests for chemical properties ofaggregate.

BS EN 1744-1 1998 - Chemical analysesBS 7371: Coatings on metal fastenersPart 1: 1991: Specification for general

requirements and selectionguidelines

Part 6: 1998: Specification for hot dippedgalvanised coatings

BS 5400: Steel, Concrete and CompositeBridges.

Part 1 1988: General Statement.Part 2: 1978: Specification for Loads.Part 4: 1990: Code of Practice for Design

of Concrete Bridges.BS 5930: 1981 - Code of Practice for Site

InvestigationsBS 8002: 1994 - Earth Retaining StructuresBS 8004: 1986 - FoundationsBS EN ISO 9002: 1994. Quality Systems. Model for

quality assurance in production,installation and servicing. (FormerlyBS 5750:Part 2).

BS EN 10142 2000. Specification for continuouslyhot-dip zinc coated low carbon steelstrip and sheet for cold forming:technical delivery conditions.(Replaces BS 2989: 1982).

BS EN 10143 1993. Continuously hot-dip metalcoated sheet steel and strip.Tolerances on dimensions andshape. (Replaces BS 2989:1992)

17.4 Other Documents (reference number)

1. Poulos, H. G. and Davis E. B. - “ElasticSolutions for Soil and Rock Mechanics” - JohnWiley and Sons, 1974, Chapter 6.

2. Vogel, A. I. - “Vogel’s Qualitative InorganicAnalysis - Sixth Edition (revised by G. Svehla)” -Longman, 1987 (pp 159 - 161).


November 200117/2

Chapter 17References

3. “Relative Values of Acid Deposition in theUnited Kingdom 1986 - 1991” - available fromADAS Consultancy Ltd, ADAS Bridgets,Martyrs Worthy, Winchester, Hants SO21 1AP.

4. TRL Report 447 “Sulfate specification forstructural backfills” Reid J.M., M.A. Czerwko,J.C. Cripps and D. M. Hiller, Transport ResearchLaboratory, Crowthorne. (2001)

17.5 Bibliography

1. Meyerhof G. G. and Baikie L. D. - “Strength ofSteel Culvert Sheets Bearing against CompactedSand Backfill” Highway Research Board,Research Record No. 30, 1963. HRB, 2101Constitution Avenue, Washington DC 240418.

2. “Bridge Foundations and Sub-structures”,Department of the Environment, BuildingResearch Establishment, London 1979: HerMajesty’s Stationery Office.

3. BRE Special Digest SD1. Concrete in aggressiveground. (2001).


November 2001 18/1

18. ENQUIRIES

All technical enquiries or comments on this Standard should be sent in writing as appropriate to:

Chief Highway EngineerThe Highways AgencySt Christopher HouseSouthwark Street G CLARKELondon SE1 0TE Chief Highway Engineer

Chief Road EngineerScottish Executive Development DepartmentVictoria QuayEdinburgh J HOWISONEH6 6QQ Chief Road Engineer

Chief Highway EngineerThe National Assembly for WalesCynulliad Cenedlaethol CymruCrown BuildingsCathays Park J R REESCardiff CF10 3NQ Chief Highway Engineer

Director of EngineeringDepartment for Regional DevelopmentRoads ServiceClarence Court10-18 Adelaide Street G W ALLISTERBelfast BT2 8GB Director of Engineering

Chapter 18Enquiries

A1. The manufacturer or supplier will be required toobtain from The Highways Agency of the Departmentof Transport, Local Government and the Regions, aType Approval Certificate for any bolted segmental orhelically wound structure before it may be offered in atender. Separate Certificates must be obtained forbolted segmental and helically wound structures.

A2. The following evidence and information isrequired by Safety, Standards and Research, CivilEngineering Division, The Highways Agency:

A.2.1. A full technical specification of theproduct supported by two copies of theManufacturer’s Design Manual and anyrelevant current British Board ofAgrément Roads and BridgesCertificates or equivalent. In the case ofarch profile structures, thearrangements to connect the corrugatedsteel plates to the reinforced concreteshall be fully described. In the case ofhelically wound structures, a currentBritish Board of Agrément Roads andBridges Certificate is mandatory.

A.2.2. Confirmation that all the requirementsof this Standard are satisfied.

A.2.3. The minimum yield strength fy (N/mm2)

of the steel forming the structure.

A.2.4 The results of tests carried out todetermine the nominal seam strengths(kN/m) to be used in the design of thestructure. These tests shall be carriedout and reported on as described inAnnex B.

A.2.5. A specification for the bolts and nutsemployed and the European or nationalStandard(s) which they meet. Therecommended range of torque values(kN.m) applied to the bolts shall bestated.

A.2.6. The results of tests carried out todetermine the tensile strengths (kN/m)of the lockseams in helically woundcorrugated steel. The lockseams testsshall be able to withstand the forces asdescribed in Annex C.

A.2.7. Evidence that the manufactureroperates a Quality Control Systemconforming to BS EN ISO 9002:1994.

A.3. The continuing validity of the Certificate isconditional upon an acceptable quality of workmanshipand materials being maintained and upon satisfactoryfindings from checks and tests which The HighwaysAgency or its authorised representatives will make fromtime to time either on site or at the manufacturer’spremises.

A.4. Any variation in the specification of a productthat has been submitted to The Highways Agencyshould be notified immediately. Failure to do so mayresult in the withdrawal of the Type ApprovalCertificate.

A.5. Applications for Type Approval of boltedsegmental products from suppliers and manufacturersshould be made to The Highways Agency, Safety,Standards and Research, Civil Engineering Division.The basis for the granting of type approval ofcorrugated steel buried structures by the HighwaysAgency is:

A.5.1. Verification that the applicant hassubmitted all the evidence required byClause A2.

A.5.2. Verification that the technicalspecification of the product meets therequirements of the Standard.

A.5.3. Verification that the requirements of theStandard are met.

A.5.4. Verification that the stated minimumyield strength is achievable for the steelgrade specified in the technicalspecification of the product.

ANNEX A: PROCEDURE AND CONDITIONS FOROBTAINING A TYPE APPROVAL CERTIFICATE FORCORRUGATED STEEL BURIED STRUCTURES

Annex AProcedure and Conditions for Obtaining A Type Approval Certificate for

Corrugated Steel Buried Structures

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November 2001

A.5.5. Verification that the nominal seamstrength/bolt configuration has beencorrectly derived in accordance withAnnex B following evaluation by TheHighways Agency, Safety, Standardsand Research, Civil EngineeringDivision of the acceptability of theseam strength test results in terms oftheir technical reliability.

A.5.6. Verification that the nuts and bolts meetthe applicant’s stated national standardand have been used in the tests in A.5.5.above.

A.5.7 Verification that the manufactureroperates a Quality Control Systemconforming to BS EN IOS 9002: 1994.

A.6. Applications for Type Approval of helicallywound products from suppliers and manufacturersshould be made to The Highways Agency, Safety,Standards and Research, Civil Engineering Division.The basis for the granting of type approval ofcorrugated steel buried structures by the HighwaysAgency is:

A.6.1. Verification that the applicant hassubmitted all the evidence required byClause A2.

A.6.2. Verification that the technicalspecification of the product meets therequirements of the Standard.

A.6.3. Verification that the requirements of theStandard are met.

A.6.4. Verification that the stated minimumyield strength is achievable for the steelgrade specified in the technicalspecification of the product.

A.6.5. Verification that the lockseam strengthmeets the requirements of Annex C. Acurrent British Board of Agrément(BBA) Certificate or equivalent shall besubmitted to The Highways Agency,Safety, Standards and Research, CivilEngineering Division in accordancewith Clause 1.6.

A.6.6. Verification that the manufactureroperates a Quality Control Systemconforming to BS EN IOS 9002: 1994.

A.7. When all the above information has beenverified, a Type Approval Certificate is issued. Allcorrugated steel buried structures which have beengiven Type Approval are listed in Advice Note SA1(MCHW 0.3.1 Annex B). Type Approval previouslygranted is liable to be withdrawn at any time followingnon-compliance with any of the requirements set out inthis Annex.

Annex AProcedure and Conditions for Obtaining A Type Approval Certificate forCorrugated Steel Buried Structures

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B.1. For bolted segmental structures, the manufacturershall submit to The Highways Agency of TheDepartment of Transport, Local Government and theRegions the results of tests on longitudinal bolted jointsto determine the nominal seam strengths to be used inthe design of the structures. These will be required foreach combination of plate thickness and boltarrangement to be certified. The tests shall beperformed at a laboratory accredited by NAMAS orequivalent, for the appropriate compression testing andcarried out in accordance with the procedures set outbelow. Tests in accordance with national standards ofEuropean Economic Area states which are equivalent tothe tests stated in this document will be deemed to beacceptable.

B.2. Test Samples

B.2.1. For each plate thickness and bolt arrangement tobe tested, at least three samples, each with alongitudinal seam across it, shall be prepared frommaterials which are fully representative of themanufactured product, except that the samples need nothave any protective coating. The samples shall beformed from corrugated but uncurved steel plates andeach will include an even number of corrugations with aminimum of two.

B.2.2. Two parallel flat end-plates are to be welded tothe two edges normal to the plane of the corrugatedplate, to act as compression bearing surfaces. The flatend-plates shall be rectangular and shall extend at least30mm in each direction beyond the welded ends of thecorrugated sample. The welded length shall not exceeda distance of half the longitudinal bolt spacing beyondthe last bolt in each direction.

B.2.3. The sample shall be of sufficient length to allowthe permitted joint displacement without the corrugatedplates touching the opposite end plate and the weld.

B.2.4. The bolt arrangement shall be representative ofthe joints proposed. The bolts shall be torqued to avalue agreed with The Highways Agency.

B.3. Test Procedure

B.3.1. The seam strength tests shall be undertaken by alaboratory accredited by the National Measurement and

Accreditation Services, NAMAS, or equivalent toundertake compression tests in the load range requiredfor the tests.

B.3.2. A compression testing machine of suitablecapacity and capable of applying the load at a uniformrate and maintaining it during slipping of the joint shallbe used. It shall be equipped with bearing platens whichare to be at least as large as the sample. Any horizontalmovement of the sample shall be prevented. Unless themachine can record both load and deflection, two dialgauges reading accurately to 0.1mm shall be mountedbetween the platens on either side of the sample and onits longitudinal centre line.

B.3.3. The sample shall be placed in the machine so thatthe applied load will not be eccentric to the sample. Itshall then be loaded in approximately 20 equally spacedload increments which are to be determined on the basisof previous experience. In the absence of suchexperience, a trial test should be carried out.Alternatively, when the load can be appliedautomatically it shall be applied continuously with therate of deformation not exceeding 5mm per minute andthe load displacement recorded automatically.

B.3.4. Unless the load has been applied automatically asdescribed in B.3.3. above, a record of load anddeflection shall be taken and plotted, the deflectionbeing the average recorded by the two dial gauges.

B.4. Nominal Seam Strength

B.4.1. The seam strength for each sample tested shall bedetermined from the least of the following:

i. The load (kN) recorded at failure,

ii. The load (kN) corresponding to a jointdisplacement in the direction of loading equal tothe lesser of the amplitude of the corrugation or40mm,

iii. Three times the load corresponding to one thirdof the displacement at failure.

B.4.2. The nominal longitudinal seam strength (kN/m)of a particular combination of plate thickness and boltarrangement shall be taken as the average of three seamstrength test results, provided the lowest value is within

ANNEX B: LONGITUDINAL SEAM STRENGTH FORBOLTED SEGMENTAL STRUCTURES

Annex BLongitudinal Seam Strength for Bolted Segmental Structures

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10% of the highest. Results from samples that fail byshearing of the bolts shall not be allowed.

B.5. Reporting of Test Results

The manufacturer shall submit to The HighwaysAgency a report prepared by the testing establishmentgiving the following details:

NAMAS Accreditation Certificate or equivalent forcompression testing in the range required.

Sample identification marks and numbers.

Statement of test procedure.

Plate thickness and corrugation details.

Bolt type, size and arrangement and strengthdesignation.

Method of forming the bolt holes and hole size.

Plot of load against displacement for each test.

Description of the mode of failure for each test.

Ultimate load and corresponding displacement for eachtest.

Load at displacement equal to the amplitude of thecorrugation or 40mm (as appropriate).

Proposed nominal seam strength (kN/m) for eachcorrugation/bolt arrangement.

Photographs of each test sample after failure.

B.6. Retention of Samples

After testing the samples shall be retained by themanufacturer for a period of at least three monthsfollowing receipt by The Highways Agency of thereport required by Clause B.5. The samples shall bestored in such a way that they can be readily inspectedif required.

Annex BLongitudinal Seam Strength for Bolted Segmental Structures

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C1 Lockseams shall be able to withstand tensile forces across the seam, according to steel sheet thickness, astabulated below:

Nominal Sheet Thickness Minimum Tensile(mm) Force across Seam

(kN/m)

1.00 36

1.30 51

1.60 65

2.00 88

2.80 136

3.50 182

4.20 234

For intermediate sheet thicknesses, the minimum tensile force required may be determined by linear interpolation.

ANNEX C: SPECIFICATION FOR TENSILESTRENGTH OF LOCKSEAMS IN HELICALLYWOUND CORRUGATED STEEL STRUCTURES

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Annex CSpecification for Tensile Strength of Lockseams in Helically Wound

Corrugated Steel Structures

DMRB VOLUME 2 SECTION 2 PART 6 - BD 12/01 - DESIGN OF ...

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