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Design and Construction Guide

Reinforced Concrete MasonryCantilever Retaining Walls

Concrete Masonry Association of Australia Limited

Reinforced Concrete MasonryCantilever Retaining Walls –Design and Construction Guide

Concrete Masonry Association of Australia

Reposted with corrections to Pages 33 & 35,September 2003

Reposted with corrections to Pages 35 & 36,July 2003

Reposted with corrections to Pages 8, 9, 10, 11 & 36,April 2003

Reposted with corrections to pages 1 & 41May 2003

First posted on web, March 2003

© 2003 Concrete Masonry Association of Australia.

Except where the Copyright Act allows otherwise, no part of thispublication may be reproduced, stored in a retrieval system in anyform or transmitted by any means without prior permission in writing ofthe Concrete Masonry Association of Australia.

The information provided in this publication is intended for generalguidance only and in no way replaces the services of professionalconsultants on particular projects. No liability can therefore beaccepted by the Concrete Masonry Association of Australia for its use.

It is the responsibility of the user of this Guide to check the ConcreteMasonry Association of Australia web site (www.cmaa.com.au) for thelatest amendments and revisions.

ISBN 0 909407 49 5


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Concrete MasonryAssociation of

Australia Limited

ABN 33 065 618 840

Level 6, 504 Pacific HighwaySt Leonards NSW 2065(P0 Box 572 St Leonards NSW 1590)

Telephone: 02 9903 7760Facsimile: 02 9437 9703E-mail: [email protected]

Internet: www.cmaa.com.au

Preface

Standards Australia has published AS 4678-2002 forthe design of earth retaining structures, includingreinforced concrete masonry cantilever retainingwalls. It encompasses the following features: ■ Limit state design

■ Partial loading and material factors

■ Compatibility with the general approach taken inAS 1170 SAA Loading code(Note 1)

■ Compatibility with the structures standards suchas AS 3600 Concrete structures(Note 2) and AS 3700Masonry structures.

This guide provides Australian designers andcontractors with a comprehensive approach to thedesign and construction of reinforced concretemasonry cantilever retaining walls based on:■ The design and construction rules set out in

AS 4678-2002■ An analysis method developed by the Concrete

Masonry Association of Australia (CMAA) to fitAustralian experience.

This guide describes the design and construction ofgravity earth retaining structures, consisting of areinforced concrete footing and a reinforcedconcrete masonry cantilever stem.It includes:■ A description of the principal features of the

Australian Standard■ A description of the analysis method

■ Design tables for a limited range of soilconditions and wall geometry

■ A design example which demonstrates the use ofthe Australian Standard and analysis method

■ A site investigation check list

■ A detailed construction specification.

NOTES:1 When published in early 2002, AS 4678 included load

factors which were compatible with the load factors on theversion of AS 1170 that was then current. However, changesto AS 1170 in late 2002 have meant that exact similarity ofload factors no longer exists.

2 Design of the concrete base is based on Cement andConcrete Association of Australia and Standards AustraliaReinforced Concrete Design Handbook, HB71–2002.


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Contents

1 Introduction 41.1 General 4

1.2 Glossary 4

1.3 Behaviour of Reinforced Concrete Masonry Cantilever Retaining Walls 5

1.4 Importance of a Geotechnical Report 6

1.5 Safety and Protection of Existing Structures 6

1.6 Global Slip Failure 6

1.7 Differential Settlement 7

1.8 Importance of Drainage 7

2 Design Considerations 82.1 Scope 8

2.2 Limit State Design 8

2.3 Partial Loading and Material Factors 8

2.4 Load Combinations and Factors for Stability 8

2.5 Load Combinations and Factors for Strength of Components 9

2.6 Live Loads 9

2.7 Earthquake Loads 9

2.8 Wind Loads 9

2.9 Hydraulic Loads 9

2.10 Drained Vs Undrained Parameters 9

2.11 Capacity Reduction Factors 9

2.12 Soil Analysis Model 9

2.13 Active Pressure 10

2.14 Pressure at Rest 10

2.15 Passive Pressure 10

2.16 Bearing Failure 10

2.17 Sliding Failure 11

2.18 Overturning 11

2.19 Global slip 11

3 Design Tables 123.1 General 12

3.2 Concrete and Masonry Properties 12

3.3 Foundation Material 12

3.4 Retained Soils and Infill Material 12

3.5 Lean Back 12

3.6 Backfill Slope 12

3.7 Live Loads 12

3.8 Earthquake Loads 12

4 Appendices 13Appendix A – Design Tables 14

Appendix B – Design Example 28

Appendix C – Site Investigation 37

Appendix D – Construction Specification 39


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1 Introduction

1.1 GeneralFor many years, reinforced concrete masonrygravity retaining walls, relying on gravity loads toresist the overturning forces due to soil pressure,have been constructed using a reinforced concretemasonry stem (steel reinforcement grouted intohollow concrete blockwork), which is built on areinforced concrete footing.

In 1990 the Concrete Masonry Association ofAustralia (CMAA) published Masonry Walling GuideNo 4: Design For Earth Loads - Retaining Walls,which set out a design methodology and safe loadtables for these structures. It included:■ Ultimate load design with material factors based

on characteristic soil properties, partial loadfactors consistent with AS 1170.1 and structuredesigns to AS 3700 and AS 3600.

■ Coulomb analysis of the back fill

■ Bearing analysis using the Meyerhoff approach(including tilt and inclined load factors).

■ Sliding analyses that account for friction, passivepressure and (if appropriate) base adhesion.

These design and analysis features wereconsiderable improvement on the workingstress/assumed bearing capacity/Rankine analysisthat was then in common use.

Standards Australia AS 4678-2002 is generallyconsistent with the CMAA Guide No 4 approach(with some modifications to factors), and applies toreinforced masonry gravity retaining walls, dry-stacked masonry gravity retaining structures anddry-stacked masonry reinforced soil structures.

1.2 GlossaryLoads and limit states:Design lifeThe time over which the structure is required to fulfilits function and remain serviceable.

Dead load(Note 3)

The self-weight of the structure and the retained soilor rock.

Live load(Note 3)

Loads that arise form the intended use of thestructure, including distributed, concentrated,impact and inertia loads. It includes constructionloads, but excludes wind and earthquake loads.

Wind loadThe force exerted on the structure by wind, actingon either or both the face of the retaining wall andany other structure supported by the retaining wall.

Earthquake loadThe force exerted on the structure by earthquakeaction, acting on either or both the face of theretaining wall and any other structure supported bythe retaining wall.

Stability limit stateA limit state of loss of static equilibrium of astructure or part thereof, when considered as arigid body.

Strength limit stateA limit state of collapse or loss of structural integrityof the components of the retaining wall.

Serviceability limit stateA limit state for acceptable in-service conditions.The most common serviceability states areexcessive differential settlement and forwardmovement of the retaining wall.

Components:Concrete masonry unitsConcrete blocks manufactured to provide anattractive, durable, stable face to a retaining wall.They are commonly "H" or "Double U" configuration.

GeotextileA permeable, polymeric material, which may bewoven, non-woven or knitted. It is commonly used toseparate drainage material from other soil.

Retained materialThe natural soil or rock, intended to be retained bya retaining wall.

Foundation materialThe natural soil or rock material under a retainingwall.

Infill materialThe soil material placed behind the retaining wallfacing. Often retained soil is used for this purpose.

NOTES:3 This Guide uses the terminology “dead load” to indicate

permanent loads and “live load” to indicate imposed loads.This terminology is consistent with the convention adoptedin AS 4678-2002.

Drainage materialThe crushed rock, gravel or similar material placedbehind a retaining wall to convey ground wateraway from the wall and foundations. It is commonlyused in conjunction with other drainage media, suchas agricultural pipes.

Soil types:Cohesive fillNaturally-occurring or processed materials withgreater than 50% passing the 75 µm Australianstandard sieve, a plasticity index of less than 30%and a liquid limit of less than 45%.

Controlled fill Class ISoil, rock or other inert material that has beenplaced at a site in a controlled fashion and underappropriate supervision to ensure the resultantmaterial is consistent in character, placed andcompacted to an average density equivalent to 98%(and no test result below 95%) of the maximum drydensity (standard compactive effort) for the materialwhen tested in accordance with AS 1289.5.1.1. Forcohesionless soils, material compacted to at least75% Density index is satisfactory.

Controlled fill Class IISoil, rock or other inert material that has beenplaced in specified layers and in a controlledfashion to ensure the resultant material is consistentin character, placed and compacted to an averagedensity equivalent to 95% (and no test result below92%) of the maximum dry density (standardcompactive effort) for the material when tested inaccordance with AS 1289.5.1.1. For cohesionlesssoils, material compacted to at least 75% Densityindex is satisfactory. Generally the layer thickness isspecified as a maximum of 300 mm.

Uncontrolled fillSoil, rock or other inert material that has beenplaced at a site and does not satisfy the materialsincluded above.

Insitu materialNatural soil, weathered rock and rock materials.

GWWell-graded gravel as defined by the Cassegrandeextended classification system. Generally in therange of 2 mm to 60 mm, and graded such that thesmaller particles pack into the spaces between thelarger ones, giving a dense mass of interlockingparticles with a high shear strength and lowcompressibility.

SWWell-graded sand as defined by the Cassegrandeextended classification system. Generally in therange of 0.06 mm to 2 mm, and graded such thatthe smaller particles pack into the spaces betweenthe larger ones, giving a dense mass of interlockingparticles with a high shear strength and lowcompressibility.

GPPoorly-graded gravel as defined by theCassegrande extended classification system.Generally in the range of 2 mm to 60 mm, and of asingle size. This material has good drainageproperties provided it is protected from infiltrationby silts and clays.

1.3 Behaviour of ReinforcedConcrete MasonryCantilever Retaining Walls

If unrestrained, a soil embankment will slump to itsangle of repose. Some soils, such as clays, havecohesion that enables vertical and near-verticalfaces to remain partially intact, but even these mayslump under the softening influence of groundwater. When an earth retaining structure isconstructed, it restricts this slumping. The soilexerts an active pressure on the structure, whichdeflects a little and is then restrained by the frictionand adhesion between the base and soil beneath,passive soil pressures in front of the structure andthe bearing capacity of the soil beneath the toe ofthe structure.

If water is trapped behind the retaining structure, itexerts an additional hydraulic pressure. This groundwater also reduces the adhesion and bearingresistance. If massive rock formations are presentimmediately behind the structure, these will restrictthe volume of soil which can be mobilised and thusreduce the pressure.

The walls described in this guide are gravity earthretaining structures, consisting of a reinforcedconcrete footing and a reinforced concrete masonrycantilever stem (Figure 1.1). The retained soil exertsan active pressure on the infill material above theheel of the base (in Arrangement 1)and this, in turn,exerts an active force on the stem of the wall. Inarrangement 2, the retained soil exerts an activepressure directly on the stem. Overturning isresisted by the vertical load of the structure and,where applicable,the soil above the heel. It is usualto disregard any resistance to overturning providedby live loads.


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Infil material

Drainage system

TYPE 1

TYPE 2

Reinforced insitu concretebase

Reinforced concrete masonrystem

Retained soil

Drainage system

Reinforced insitu concretebase

Reinforced concrete masonrystem

Retained soil

Figure 1.1 Typical Arrangements of ReinforcedConcrete Masonry CantileverRetaining Walls

1.4 Importance of aGeotechnical Report

The design of a retaining wall includes two essentialparts:■ Analysis of the adjacent ground for global slip,

settlement, drainage and similar globalconsiderations; and

■ Analysis and design of retaining wall structure forstrength.

These analyses must be based on an accurate andcomplete knowledge of the soil properties, slopestability, potential slip problems and groundwater.A geotechnical report by a qualified andexperienced geotechnical engineer should beobtained.

Such a report must address the followingconsiderations, as well as any other pertinent pointsnot listed.■ Soil properties;

■ Extent and quality of any rock, including floatersand bedrock;

■ Global slip and other stability problems;

■ Bedding plane slope, particularly if they slopetowards the cut;

■ Effect of prolonged wet weather and theconsequence of the excavation remaining openfor extended periods;

■ Effect of ground water;

■ Steep back slopes and the effect of terracing;

■ Effect of any structures founded within a zone ofinfluence.

1.5 Safety and Protection ofExisting Structures

Whenever soil is excavated or embankments areconstructed, there is a danger of collapse. This mayoccur through movement of the soil and anyassociated structures by:■ rotation around an external failure plane that

encompasses the structure,■ slipping down an inclined plane,

■ sliding forward, or

■ local bearing failure or settlement.

These problems may be exacerbated by theintrusion of surface water or disruption of the watertable, which increase pore water pressures and thusdiminish the soil’s ability to stand without collapse.

The safety of workers and protection of existingstructures during construction must be of primeconcern and should be considered by bothdesigners and constructors. All excavations shouldbe carried out in a safe manner in accordance withthe relevant regulations, to prevent collapse thatmay endanger life or property. Adjacent structuresmust be founded either beyond or below the zone ofinfluence of the excavation. Where there is risk ofglobal slip, for example around a slip planeencompassing the proposed retaining wall or otherstructures, or where there is risk of inundation byground water or surface water, construction shouldnot proceed until the advice of a properly qualifiedand experienced Geotechnical Engineer has beenobtained and remedial action has been carried out.

1.6 Global Slip FailureSoil retaining structures must be checked for globalslip failure around all potential slip surfaces orcircles (Figure 1.2).

Designers often reduce the heights of retainingwalls by splitting a single wall into two (or more)walls, thus terracing the site. Whilst this may assistin the design of the individual walls, it will notnecessarily reduce the tendency for global slipfailure around surfaces encompassing all or someof the retaining walls.

The designer should also take into account theeffects of rock below or behind the structure inresisting slip failure.

Analysis for global slip is not included in this guideand it is recommended that designers carry out aseparate check using commercially availablesoftware.


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Globalslip plane

Primaryglobal slip plane

Secondaryglobal slipplane

Figure 1.2 Global Slip Failure

1.7 Differential SettlementTechniques to reduce or control the effects ofdifferential settlement and the possibility of crackinginclude:■ Articulation of the wall (by discontinuing the

normal stretcher bond) at convenient intervalsalong the length.

■ Excavating, replacing and compacting areas ofsoft soil.

■ Limiting the stepping of the base to a maximumof 200 mm.

1.8 Importance of DrainageThis guide assumes that a properly-functioningdrainage system is effective in removing hydraulicpressure. If this is not the case, the designer will berequired to design for an appropriate hydraulicload.

Based on an effective drainage system, it iscommon to use drained soil properties. For othersituations, the designer must determine whetherdrained or undrained properties are appropriate. Inparticular, sea walls that may be subject to rapiddraw-down (not covered in this guide) requiredesign using undrained soil properties.


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Infill material

Surface seal of 150-mm-thick compacted clay

Geofabric separation layer between drainage fill materialand retained fill material

10-mm crushed rock drainage fill material placed aroundthe drainage pipe for a minimum of 300 mm and extendingup the back of the wall

100-mm-dia. slotted PVC agricultural pipe wrapped ingeofabric sock, laid to a minimum uniform grade of 1 in 100over 15-m length. The low end of each run is to be drainedthrough the hob to a stormwater system. The upper end ofeach run is to be brought to the surface and capped

50-mm-dia. weepholes through hob at 1200 mm centres

Retained soil

Key

Base

Hob

Optionalcapping

Concretemasonry

stem

100-mm-deep catch drain with a minimum grade of1 in 100 connected to the site drainage system

Figure 1.3 Typical Drainage System

2 DesignConsiderations

2.1 ScopeThis guide considers retaining walls founded onundisturbed material that is firm and dry andachieves the friction angle and cohesion noted foreach particular soil type. It does not coverfoundations exhibiting any of the followingcharacteristics:■ Softness■ Poor drainage■ Fill■ Organic matter■ Variable conditions■ Heavily-cracked rock■ Aggressive soils.

If these conditions are present, they must beconsidered by the designer.

2.2 Limit State DesignThe design limit states considered are:■ strengths of the various components subject to

ultimate factored loads;■ stability of the structure as a whole subject to

ultimate factored loads; and■ serviceability of the structure and its components

subject to service loads.

2.3 Partial Loading andMaterial Factors

Partial-loading and partial-material factors enablethe designer to assign various levels of confidenceto assumed or measured soil strengths, materialstrengths and resistance to deterioration,predictability of loads and consequence of failure ofvarious structures.

There are several reasons for compatibility ofloading factors between AS 4678-2002 and AS 1170SAA Loading code, which applies to buildings(Note 4).■ Buildings are often constructed close to retaining

walls, and therefore apply loads on them. ■ Parts of buildings such as basement walls are

often required to withstand loads imposed byearth and soil.

■ The adoption of common load factors assists therational comparison of the levels of safety andprobability of failure of retaining walls and otherstructures.

■ The design of concrete, masonry, steel andtimber components of earth retaining structuresis determined using Australian Standards whichare based on limit state concepts and loadingfactors from AS 1170.

■ Most structural engineers are familiar with theloading factors of AS 1170.

2.4 Load Combinations andFactors for Stability

The following load combinations and factors shouldbe applied when checking the stability of thestructure. This includes analysis for: ■ Global slip■ Overturning■ Bearing capacity of the foundation under the toe

of the base■ Sliding resistance of the foundation under the

base(Note 5).

(i) 1.25 GC + 1.5 QC < 0.8 GR + (Φ R)

(ii) 1.25 GC + ψc QC + WCu < 0.8 GR + (Φ R)

(iii) 1.25 GC + ψc QC + 1.0 FCeq < 0.8(G + ψcQ)R + (Φ R)

Where:

GC = parts of the dead load tending to causeinstability.This includes:

the weight of the retained soil, whichcauses horizontal pressures on the stem,thus tending to cause forward sliding,bearing failure or overturning, or theweight of the infill soil, which causeshorizontal pressures on the facing, thustending to cause stem rupture.

QC = parts of the live load tending to causeinstability.

This includes all removable loads such astemporary loadings, live loadings appliedfrom adjacent buildings, construction trafficand soil compaction loads and anallowance for the temporary stacking of soilof not less than 5 kPa, except for StructureClassification 3.

WCu = parts of the wind load tending to cause

instability.The factors are such that load combination(ii) involving wind loading, will not be thegoverning case when the effect due towind, WC

u is less than (1.5 - ψc) times theeffect due to live load, QC.For example, for a wall that does notsupport another exposed structure and fora minimum live load surcharge ofQC = 5 kPa, an active pressure coefficientof Ka = 0.3 and a live load combinationfactor of ψc = 0.6, a wind load on the faceof the retaining wall less than 1.35 kPa willnot be the governing case. However, if thewind load is applied to some supportedstructure such as a building or a fence, theeffect would be more pronounced.


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NOTES:4 When published in early 2002, AS 4678 included load

factors which were compatible with the load factors on theversion of AS 1170 that was then current. However, changesto AS 1170 in late 2002 have meant that exact similarity ofload factors no longer exists.

5 Design for bearing capacity and external sliding resistance,involve the factoring-down of the soil properties (density,friction angle and/or cohesion) which are providing theresistance to instability.

FCeq = parts of the earthquake load tending to

cause instability.For earthquake categories Ae and Be,design for static loads without furtherspecific analysis is deemed adequate. For earthquake category Ce, a dead loadfactor of 1.5 (instead of 1.25) should beused and specific design for earthquakemay be neglected.For earthquake categories De and Ee, thestructures should be designed andanalysed in accordance with the detailedmethod set out in AS 4678 Appendix I.

GR = parts of the dead load tending to resistinstability.

This includes the self weight of thestructure and the weight of soil in front ofthe structure.

ΦR = the factored design capacity of thestructural component.

This includes calculated bearing capacity,sliding resistance, calculated pull-outstrength, etc.

ψc = live load combination factor.This is taken as 0.4 for parking or storageand 0.6 for other common applications onretaining walls.

2.5 Load Combinations andFactors for Strength ofComponents

The following load combinations and factors shouldbe applied when checking the strength of thestructure components, including strength of anyassociated concrete, masonry and reinforcement.

(i) 1.25 G + 1.5 Q

(ii) 1.25 G + Wu + ψc Q

(iii) 1.25 G + 1.0 Feq + ψc Q

(iv) 0.8 G + 1.5 Q

(v) 0.8 G + Wu

(vi) 0.8(G + ψc Q) + 1.0Feq

Where:G = dead load

Q = live load

Wu = wind load

Feq = earthquake load

ψc = live load combination factor taken as0.4 for parking or storage and 0.6 forother common applications onretaining walls.

2.6 Live LoadsThe appropriate values for live load must bedetermined by the design engineer. AS 4678–2002specifies a minimum live loading of 5 kPa for wallsof any height of Structure Classifications 1 and 2.

For walls under 1.5 metres high which are ofStructure Classification 3, the following minimum liveloads are applicable.

Slope of retained soil less than or equal to 1:4 –2.5 kPa

Slope of retained soil greater than 1:4 –1.5 kPa

2.7 Earthquake LoadsThe appropriate earthquake loads must bedetermined by the designer. If earthquake load actson some supported structure such as a building ora fence, the effect must be considered.

2.8 Wind LoadsThe load factors are such that load combination (ii)involving wind loading, will not be the governingcase when the effect due to wind, WC

u is less than

(1.5 - ψc) times the effect due to live load, QC.For example, for a wall that does not supportanother exposed structure and for a minimum liveload surcharge of QC = 5 kPa, an active pressurecoefficient of Ka = 0.3 and a live load combinationfactor of ψc = 0.6, a wind load on the face of theretaining wall less than 1.35 kPa will not be thegoverning case. However, if the wind load is appliedto some supported structure such as a building or afence, the effect must be considered.

2.9 Hydraulic LoadsThe design example is based on the assumptionthat a properly-functioning drainage system iseffective in removing hydraulic pressure.

2.10 Drained v UndrainedParameters

Based on an effective drainage system, the designexample uses drained soil properties. For othersituations, the designer must determine whetherdrained or undrained properties are appropriate.

2.11 Capacity Reduction FactorsThe material strength factors from AS 4678Table 5.1 have been used.

2.12 Soil Analysis ModelAS 4678 does not specify an analysis method. Thisguide uses the Coulomb Method to analyse thestructure.


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2.13 Active PressureIn response to soil pressure, the wall will move awayfrom the soil, thus partially relieving the pressure.This reduced pressure is the active pressure. TheCoulomb equation for active pressure coefficient(Ka) can account for slope of the wall and slope ofthe backfill. The slope of the wall should berestricted to less than external angle of friction (δ) toensure that there is no upward component of earthpressure which would reduce sliding resistance(ie the equation applies when wall slope is less than15° for good quality granular backfills in contactwith concrete).

pa = active pressure on the wall at depth of H= Ka γH

Where:Ka = active pressure coefficient

=cos2(φ + ψ)

cos2ψcos(ψ - δ) 1+sin(φ + δ) sin(φ - β) 2

√cos(ψ - δ) cos(ψ + β)

φ = factored value of internal friction angle(degrees)

δ = external friction angle (degrees)

= 2φ3

where φ is the smaller of the friction anglesat the particular interfaceAt any interface with a geotextile, theexternal friction angle should be taken fromtest data. If no data is available, it shouldbe assumed to be zero.

ψ = slope of the wall (degrees)

β = slope of the backfill (degrees)

γ = factored value of soil density (kN/m3)

H = height of soil behind the wall (m)

2.14 Pressure at RestIf the wall is unable to move away from the soilembankment, as may be the case for a proppedcantilever basement wall, there will be no relief ofthe pressure and the soil will exert the full pressureat rest.

po = soil pressure at rest

= Ko γH

Where:Ko = coefficient for soil at rest

= 1.0


H = height of soil behind the wall (m)

2.15 Passive PressureIf the structure pushes into the soil, as is the case atthe toe of a retaining wall, the resistance by the soilis greater than the pressure at rest. This is thepassive pressure, given by the following equation. Ifthe soil in front of the toe is disturbed or loose, thefull passive pressure may not be mobilised.

pp = passive soil pressure (kPa)

= Kp γHe

Where:Kp = passive pressure coefficient

=1 + sin φ1 - sin φ

φ = factored value of internal friction angle(degrees)


He = depth of undisturbed soil to the undersideof the base, key or bearing pad asappropriate (m)

2.16 Bearing FailureAs soil and water pressure are applied to the rearface of the structure, it will tilt forward and the soilunder the toe is subjected to high bearingpressures. Bearing is often the critical mode offailure. The following theoretical approach is used toanalyse this region for bearing pressure failure andis based the Meyerhof method. This givesconsideration to footing width, footing tilt and angleof applied load and is explained in a paper by Vesictitled Bearing Capacity of Shallow Footings in theFoundation Engineering Handbook.

Q = Bearing capacity of the foundation (kN)= qav LB

Where:qav= average bearing capacity based on

factored soil properties (kPa)B = actual base width (m)

LB = effective width of base (m)

c = factored value of drained cohesion (kPa)

φ = factored value of friction angle (radians)



Nc = (Nq - 1)cot φ

Nq = eπtan φ tan 2[π/4 + φ/2]

Nγ = 2(Nq + 1)tan φ

Shape factors:ζc = 1.0

ζq = 1.0

ζγ = 1.0


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= c Nc ζc ζci ζct + γHe Nq ζq ζqi ζqt + 0.5 γB Nγζγζγi ζγt

Factors for inclined load:ζci = ζqi - (1 - ζqi) /(Nc tan φ)

ζqi = [1 - P*/(Q* + LB c cot φ)]2

ζγi = [1 - P*/(Q* + LB c cot φ)]3

Factors for sloping bases:ζct = ζqt - (1 - ζqt) / (Nc tan φ) =1.0 for level base

ζqt = (1 - α tan φ)2 =1.0 for level base

ζ γt= (1 - α tan φ)2 =1.0 for level base

Q* = vertical load based on factored loads andsoil properties

P* = horizontal load based on factored loadsand soil properties

α = angle of base in radians

2.17 Sliding FailureAs soil and water pressure are applied to the rearface of the structure, the footing may slide forward.Such sliding action is resisted by the friction andadhesion between the foundation material and thefooting, and the passive resistance of any soil infront of the toe.

When considering passive resistance, note thatmaterial can be inadvertently removed from the toeof the wall.

F = Sliding resistance based on factoredcharacteristic soil properties

= Friction + adhesion + passive resistance= Q* tan δ + c B + Kp 0.5 γHe

2

Where:

Q* = vertical load based on factored loads andsoil properties

δ = external friction angle of the soil calculatedfrom the factored internal friction angle,assuming a smooth base-to-soil interface(if a rough base-to-soil interface is present,a friction angle of φ may be used)

B = actual base width (m)

c = factored value of adhesion (kPa)

Kp = passive pressure coefficient



2.18 OverturningAS 4678-2002 does not specify an analysis method.This guide considers overturning about a point levelwith the underside of the key and a nominateddistance behind the toe of the structure. If thisnominated distance is one third of the base widthand the factor against overturning is calculated as1.0, this corresponds to the reaction being situatedwithin the middle third of the base at ultimate loads.

2.19 Global slipAS 4678-2002 Clause 3.2 requires stability(including rotation) to be checked.

The design example and design tables do notinclude analysis for global slip.


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3 Design Tables

3.1 GeneralThis section describes the design parameterscovered by the Typical Design Tables set out inAppendix A. The Tables apply to structureclassification 2 (see Site Investigation, Appendix C).

3.2 Concrete and MasonryProperties

The design example is based on:■ Hollow concrete blocks with characteristic

compressive strength, f’uc, of at least 15 MPa;■ Mortar Type M3;■ Reinforcement grade 500 MPa;■ Concrete with characteristic compressive

strength, f’c, of at least 20 MPa.

3.3 Foundation MaterialThe Tables in this guide are based on foundationmaterials with characteristic internal friction anglesof 25°, 30° and 35°.

In some cases, the lower friction angles requireeither wide bases or deep keys. To avoid thissituation, one design option is to remove anymaterial with a low friction angle and replace it witha more suitable material with a characteristic frictionangle of at least 35°. Typically, compacted roadbase would be suitable in such an application. Thefoundation soil should be excavated and replacedwith compacted road base to a depth such thatsliding and bearing resistance can be achieved.

For simplicity, the Tables are based on materialswith the following properties:Characteristic internal friction angles 25° 30° 35°Characteristic density (kg/m3) 19 19 19Characteristic cohesion (kPa) 5.0 2.5 0

In all cases, an experienced civil or geotechnicalengineer should be engaged to determine theappropriate soil properties.

The Tables are based on a rough interface betweenthe base and the foundation, such that the internalangle of friction, φ, is applicable.

3.4 Retained Soils and InfillMaterial

The design example indicates how to design fordifferent retained soils and infill material. Forsimplicity, the Tables are based on materials withthe following properties:Characteristic internal friction angles 25° 30° 35°Characteristic density (kg/m3) 19 19 19Characteristic cohesion (kPa) 5.0 2.5 0

In all cases, an experienced civil or geotechnicalengineer should be engaged to determine theappropriate soil properties.

3.5 Lean-BackConsistent with AS 4678, this guide does not coverthe design of revetments with a lean-back of 20° ormore from vertical. The tabulated typical wall detailsare applicable for vertical walls.

3.6 Backfill SlopeThe Tables in this guide have been calculated for eitherlevel backfill (0°) or 1 in 4 backfill slope (14°). For othercases,the designer must perform calculations similar tothose shown in the worked example.

3.7 Live LoadsThe Tables in this Guide have been calculated for alive loading of 5 kPa. For other cases of live loadsincluding Structure Classification 3, traffic loadingand construction loading, the appropriate valuesmust be determined by the designer.

3.8 Earthquake LoadsThe Tables in this Guide have been calculated forearthquake categories Ae or Be and therefore isbased on design for static loads without furtherspecific analysis. For other cases, the appropriateearthquake loads must be determined by thedesigner. If earthquake load acts on somesupported structure such as a building or a fence,the effect must be considered.

3.9 Position of KeyThe Tables have been based on placing the key(if required) at the rear of the base.This hasconstruction advantages, as well as simplifying thereinforcement arrangement. Other key positions maybe more appropriate in particular applications. Ifother locations are adopted, calculations will berequired to check the stability.

3.10 Stem DimensionsThe Tables include the following stem types:■ 140 mm hollow block■ 190 mm hollow block■ 290 mm hollow block■ Two leaves of 190 mm hollow block, separated

by a cavity of 80 mm and joined by steel ties toprevent spreading during the grouting process,or peeling of the thin stem away form the thickstem.This arrangement gives a total width of460 mm.

The stem width may be progressively increaseddown the wall to cater for increasing loads.

3.11 Control JointsControl joints should be included in the stem atcentres up to 16.0 m, depending on the soil typeand quantity of horizontal reinforcement that isincorporated.

3.12 HobReinforced concrete footings for retaining walls shouldinclude a means of positively locating the steel starterbars accurately and a means of providing drainagethrough the wall at the level of the base. Bothrequirements may be achieved by including a concretehob (or up-stand), through which vertical starter barsare placed and on which the masonry is built.Horizontal 50-mm diameter weep holes may passthrough the hob at 1.2 m maximum centres.


12

4 Appendices

The following Appendices are included:

Appendix A – Design Tables 14

Appendix B – Design Example 28

Appendix C – Site Investigation 37

Appendix D – Construction Specification 39


13

Appendix A Design Tables


14

DESIGN TABLES FOR TYPE 1 WALLS Typical Details

Longitudinal reinforcementin thin stem: N12 at 400 crs.

N16 700 lapN20 1000 lap

N16 700 lapN20 1000 lap

Y-bars

Y-bars

N16 at300 crs

X-bars

H1

H4

H5

100

H2

H3

B2

B4 T1

T2

B3

B1

WALLS WITH THIN STEM OF 190-mm BLOCKAND THICK STEM OF 290-mm BLOCK

700lap X-bars

Y-bars

Y-bars

Longitudinal reinforcementin thick stem: N16 at 400 crs.

Sloping backfill(1 in 4 maximum)or level

T3


Y-bars

Y-bars

N16 at300 crs

X-bars

H1

H4

H5

100

H2

H3

B2

B4 T1

T2

B3

B1

WALLS WITH THIN STEM OF 190-mm BLOCKAND THICK STEM OF 190/80/190-mm CAVITY BLOCK

700lap

X-bars

Y-bars

Y-bars

Longitudinal reinforcementin thick stem: 2-N16 at 400 crs.


T3

Longitudinal reinforcement:N12 at 400 crs.

700lap

100

Clear cover‡

Clearcover‡

65*

70*

Remove face ofblock to providea clean-outopening at eachvertical bar

Y-bars

Y-bars

N16 at300 crs

X-bars

H1

100

H2

H3

B2

B4 T1

T3

B3

B1

WALLS WITH SINGLE STEM OF 190-mm BLOCK

COMMON DETAILS FOR ALL WALLS

DESIGN TABLES SELECTION CHART

Table number (page number) for…Foundationinternalfrictionangle

Backfill slope

0° (level) 14° (1 in 4) max

Y-bars


35°

30°

25°

1 (15)

3 (17)

5 (19)

2 (16)

4 (18)

6 (20)

Longitudinal reinforcement:N12 at 400 crs.

500lap

Y-bars

Y-bars

N16 at300 crs

X-barsH1

100

H2

H3

B2

B4 T1

T3

B3

B1


Y-bars


Infill material


10-mm crushed rock drainage fill material, minimum 300 mmthick, around drainage pipe and extending up the wall



* Design depth of steel from face of masonry or concrete to centreline of reinforcement. If this must be varied (for reasons of durability, block dimensions, etc) it may render the information in the Tables inaccurate.

‡ For clear cover requirements, refer AS 3700 Section 5 and AS 3600 Section 4

Ties: N10 at 400 crs. (100 cogeach end) this course, R6 at400 x 400 crs. for remainder

NOTE: All coresand cavity to befully grouted

NOTE: All coresfully grouted




15

DESIGN TABLES FOR TYPE 1 WALLS Table 1

Live load vertical surcharge = 5 kPa Backfill slope = 0° Foundation characteristic internal friction angle = 35°Height Thin stem Thick stem Base Key Hob ReinforcementH1 T1 H4 T2 H5 B1 H2 B3 H3 B2 T3 B4 X-bars Y-bars(mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm)

Characteristic internal friction angle of infill material and retained soil = 35° Characteristic cohesion = 0 kPa

3600 190 1800 460 1800 1900 500 – – – 510 100 N16 at 400 N20 at 4003400 190 1800 290 1600 1800 350 – – – 340 100 N16 at 400 N20 at 2003200 190 1800 290 1400 1700 350 – – – 340 100 N16 at 400 N20 at 4003000 190 1800 290 1200 1600 350 – – – 340 100 N16 at 400 N16 at 2002800 190 1800 290 1000 1500 350 – – – 340 100 N16 at 400 N16 at 400

2600 190 1800 290 800 1400 350 – – – 340 100 N16 at 400 N16 at 4002400 190 1800 290 600 1400 350 – – – 340 100 N16 at 400 N16 at 4002200 190 1600 290 600 1300 350 – – – 340 100 N16 at 400 N16 at 4002000 190 1400 290 600 1200 350 – – – 340 100 N16 at 400 N16 at 4001800 190 – – – 1100 250 – – – 240 100 N16 at 400 N16 at 400

1600 190 – – – 1000 250 – – – 240 100 N16 at 400 N16 at 4001400 190 – – – 900 250 – – – 240 100 N16 at 400 N16 at 4001200 140 – – – 800 200 – – – 190 100 N12 at 400 N12 at 4001000 140 – – – 700 200 – – – 190 100 N12 at 400 N12 at 400800 140 – – – 600 200 – – – 190 100 N12 at 400 N12 at 400

Characteristic internal friction angle of infill material and retained soil = 30° Characteristic cohesion = 2.5 kPa









16












3600 190 1800 460 1800 4100 500 460 470 3540 510 100 N16 at 400 N20 at 2003400 190 1800 460 1600 3900 500 460 470 3440 510 100 N16 at 400 N20 at 2003200 190 1800 290 1400 3600 350 300 400 3300 340 100 N16 at 400 N20 at 2003000 190 1800 290 1200 3400 350 300 470 3100 340 100 N16 at 400 N20 at 2002800 190 1800 290 1000 3200 350 – – – 340 100 N16 at 400 N16 at 200




17
















18








3600 190 1800 460 1800 3900 500 460 450 3440 510 100 N16 at 400 N20 at 2003400 190 1800 290 1600 3800 350 300 430 3500 340 100 N16 at 400 N20 at 2003200 190 1800 290 1400 3500 350 300 400 3200 340 100 N16 at 400 N20 at 2003000 190 1800 290 1200 3300 350 300 300 3000 340 100 N16 at 400 N16 at 2002800 190 1800 290 1000 3000 350 300 350 2700 340 100 N16 at 400 N16 at 200

2600 190 1800 290 800 2800 350 300 330 2500 340 100 N16 at 400 N16 at 2002400 190 1800 290 600 2500 350 300 300 2200 340 100 N16 at 400 N16 at 4002200 190 1600 290 600 2300 350 300 280 2000 340 100 N16 at 400 N16 at 4002000 190 1400 290 600 2100 350 300 250 1800 340 100 N16 at 400 N16 at 4001800 190 – – – 1800 250 – – – 240 100 N16 at 400 N16 at 400



1200 140 – – – 1600 200 – – – 190 100 N12 at 400 N12 at 4001000 140 – – – 1400 200 – – – 190 100 N12 at 400 N12 at 400800 140 – – – 1200 200 – – – 190 100 N12 at 400 N12 at 400


19













2600 190 1800 290 800 2500 350 300 330 2200 340 100 N16 at 400 N16 at 2002400 190 1800 290 600 2300 350 300 300 2000 340 100 N16 at 400 N16 at 4002200 190 1600 290 600 2100 350 300 280 1800 340 100 N16 at 400 N16 at 4002000 190 1400 290 600 1900 350 300 250 1600 340 100 N16 at 400 N16 at 4001800 190 – – – 1700 250 200 230 1500 240 100 N16 at 400 N16 at 400

1600 190 – – – 1500 250 200 200 1300 240 100 N16 at 400 N16 at 4001400 190 – – – 1300 250 200 180 1100 240 100 N16 at 400 N16 at 4001200 140 – – – 1200 200 – – – 190 100 N12 at 400 N12 at 4001000 140 – – – 1100 200 – – – 190 100 N12 at 400 N12 at 400800 140 – – – 900 200 – – – 190 100 N12 at 400 N12 at 400


20

DESIGN TABLES FOR TYPE1 WALLS Table 6




2600 190 1800 290 800 2800 350 300 330 2500 340 100 N16 at 400 N16 at 4002400 190 1800 290 600 2500 350 300 300 2200 340 100 N16 at 400 N16 at 4002200 190 1600 290 600 2300 350 300 280 2000 340 100 N16 at 400 N16 at 4002000 190 1400 290 600 2100 350 300 250 1800 340 100 N16 at 400 N16 at 4001800 190 – – – 1800 250 – – – 240 100 N16 at 400 N16 at 400



2000 190 1400 290 600 2700 350 350 300 2400 340 100 N16 at 400 N16 at 4001800 190 – – – 2400 250 200 230 1870 240 100 N16 at 400 N16 at 400

1600 190 – – – 2100 250 200 200 1900 240 100 N16 at 400 N16 at 4001400 190 – – – 1800 250 200 180 1620 240 100 N16 at 400 N16 at 4001200 140 – – – 1500 200 150 150 1350 190 100 N12 at 400 N12 at 4001000 140 – – – 1300 200 – – – 190 100 N12 at 400 N12 at 400800 140 – – – 1100 200 – – – 190 100 N12 at 400 N12 at 400


1000 140 – – – 2000 200 150 130 1870 190 100 N12 at 400 N12 at 400800 140 – – – 1700 200 150 100 1600 190 100 N12 at 400 N12 at 400


21

DESIGN TABLES FOR TYPE 2 WALLS Typical Details

Clear cover‡

Clearcover‡

65*

70*

Remove face ofblock to providea clean-outopening at eachvertical bar

COMMON DETAILS FOR ALL WALLS

Infill material


10-mm crushed rock drainage fill material, minimum 300 mmthick, around drainage pipe and extending up the wall



* Design depth of steel from face of masonry or concrete to centreline of reinforcement. If this must be varied (for reasons of durability, block dimensions, etc) it may render the information in the Tables inaccurate.

‡ For clear cover requirements, refer AS 3700 Section 5 and AS 3600 Section 4


Y-bars

SL72 mesh

N16 at300 crs

X-bars

H1

H4

H5

100

H2

H3

B2

B4 T1

T2

B3

B1WALLS WITH THIN STEM OF 190-mm BLOCKAND THICK STEM OF 290-mm BLOCK

700lap

X-bars

Y-bars

Y-bars

Longitudinal reinforcementin thick stem: N16 at 400 crs.


T3


Y-bars

SL72 mesh

N16 at300 crs

X-bars

H1

H4

H5

100

H2

H3

B2

B4 T1

T2

B3

B1

WALLS WITH THIN STEM OF 190-mm BLOCKAND THICK STEM OF 190/80/190-mm CAVITY BLOCK

700lap

X-bars

Ties: N10 at 400 crs. (100 cogeach end) this course, R6 at400 x 400 crs. for remainder

Y-bars

Y-bars

Longitudinal reinforcementin thick stem: 2-N16 at 400 crs.


NOTE: All cores andcavity fully grouted




T3

Longitudinalreinforcement:N12 at 400 crs.

700lap Y-bars

N16 at300 crs

X-bars

H1

100

H2

H3

B2

B4 T1

T3

B3

B1


DESIGN TABLES SELECTION CHART

Table number (page number) for…Foundationinternalfrictionangle

Backfill slope

0° (level) 14° (1 in 4) max

Y-bars


35°

30°

25°

7 (22)

9 (24)

11 (26)

8 (23)

10 (25)

12 (27)

Longitudinalreinforcement:N12 at 400 crs.

500lap

Y-bars

SL72 mesh

N16 at300 crs

X-bars

H1

100

H2

H3

B2

B4 T1

T3

B3

B1


Y-bars

SL72 mesh


100

N16 700 lapN20 1000 lap

N16 700 lapN20 1000 lap


22




3600 190 1800 460 1800 2900 500 460 200 2440 510 1740 N16 at 400 N20 at 4003400 190 1800 290 1600 2800 350 – – – 340 1910 N16 at 400 N20 at 2003200 190 1800 290 1400 2600 350 – – – 340 1710 N16 at 400 N20 at 4003000 190 1800 290 1200 2200 350 – – – 340 1510 N16 at 400 N16 at 2002800 190 1800 290 1000 1800 350 300 100 1500 340 1410 N16 at 400 N16 at 400





2600 190 1800 290 800 2100 350 300 330 1800 340 1610 N16 at 400 N16 at 4002400 190 1800 290 600 2000 350 300 300 1700 340 1410 N16 at 400 N16 at 4002200 190 1600 290 600 1800 350 300 280 1500 340 1210 N16 at 400 N16 at 4002000 190 1400 290 600 1500 350 – – – 340 1310 N16 at 400 N16 at 4001800 190 – – – 1500 250 200 230 1300 240 1110 N16 at 400 N16 at 400

1600 190 – – – 1300 250 200 200 1100 240 910 N16 at 400 N16 at 4001400 190 – – – 1100 250 – – – 240 810 N16 at 400 N16 at 4001200 140 – – – 1000 200 150 150 850 190 760 N12 at 400 N12 at 4001000 140 – – – 800 200 – – – 190 560 N12 at 400 N12 at 400800 140 – – – 700 200 – – – 190 460 N12 at 400 N12 at 400




1600 190 – – – 1500 250 200 300 1300 240 1210 N16 at 400 N16 at 4001400 190 – – – 1300 250 200 200 1100 240 1010 N16 at 400 N16 at 4001200 140 – – – 1200 200 150 200 1050 190 960 N12 at 400 N12 at 4001000 140 – – – 1000 200 150 100 850 190 760 N12 at 400 N12 at 400800 140 – – – 800 200 150 100 650 190 560 N12 at 400 N12 at 400


23





2600 190 1800 290 800 2100 350 300 330 1750 340 2110 N16 at 400 N16 at 4002400 190 1800 290 600 2000 350 300 300 1700 340 1710 N16 at 400 N16 at 4002200 190 1600 290 600 1600 350 – – – 340 1710 N16 at 400 N16 at 4002000 190 1400 290 600 1400 350 – – – 340 1810 N16 at 400 N16 at 4001800 190 – – – 1800 250 280 230 1570 240 1210 N16 at 400 N16 at 400



3000 190 1800 290 1200 3500 350 400 600 3100 340 2610 N16 at 400 N16 at 2002800 190 1800 290 1000 3100 350 300 430 2800 340 2510 N16 at 400 N16 at 200


1600 190 – – – 1500 250 200 450 1300 240 1210 N16 at 400 N16 at 4001400 190 – – – 1300 250 200 460 1100 240 1010 N16 at 400 N16 at 4001200 140 – – – 1200 200 200 470 1000 190 960 N12 at 400 N12 at 4001000 140 – – – 1000 200 150 100 850 190 760 N12 at 400 N12 at 400800 140 – – – 800 200 – – – 190 660 N12 at 400 N12 at 400


2000 190 1400 290 600 2600 350 300 400 2200 340 2210 N16 at 400 N16 at 4001800 190 – – – 2600 250 270 400 2200 240 2010 N16 at 400 N16 at 200



24





2600 190 1800 290 800 2100 350 300 330 1800 340 1410 N16 at 400 N16 at 4002400 190 1800 290 600 2000 350 300 300 1700 340 1310 N16 at 400 N16 at 4002200 190 1600 290 600 1800 350 300 280 1500 340 1110 N16 at 400 N16 at 4002000 190 1400 290 600 1400 350 – – – 340 1110 N16 at 400 N16 at 4001800 190 – – – 1500 250 200 230 1300 240 1010 N16 at 400 N16 at 400

1600 190 – – – 1300 250 200 200 1100 240 810 N16 at 400 N16 at 4001400 190 – – – 1000 250 – – – 240 710 N16 at 400 N16 at 4001200 140 – – – 1000 200 150 150 850 190 560 N12 at 400 N12 at 4001000 140 – – – 700 200 – – – 190 460 N12 at 400 N12 at 400800 140 – – – 600 200 – – – 190 360 N12 at 400 N12 at 400






2000 190 14800 290 600 2800 350 300 250 2500 340 1810 N16 at 400 N16 at 4001800 190 – – – 2500 250 240 350 2260 240 1610 N16 at 400 N16 at 400



25




3000 190 1800 290 1200 3000 350 300 400 2700 340 2310 N16 at 400 N16 at 2002800 190 1800 290 1000 2500 350 300 400 2200 340 2010 N16 at 400 N16 at 200


1600 190 – – – 1400 250 200 200 1200 240 1110 N16 at 400 N16 at 2001400 190 – – – 1200 250 200 180 1000 240 910 N16 at 400 N16 at 2001200 140 – – – 1000 200 150 150 850 190 760 N12 at 400 N12 at 2001000 140 – – – 900 200 150 100 750 190 560 N12 at 400 N12 at 200800 140 – – – 700 200 – – – 190 460 N12 at 400 N12 at 200


2400 190 1800 290 600 3400 350 300 400 3100 340 2210 N16 at 400 N16 at 2002200 190 1600 290 600 2700 350 300 400 2400 340 1910 N16 at 400 N16 at 2002000 190 1400 290 600 2100 350 300 400 1800 340 1910 N16 at 400 N16 at 2001800 190 – – – 2200 250 270 400 1930 240 1610 N16 at 400 N16 at 200



1400 190 – – – 2400 250 270 400 2130 240 1610 N16 at 400 N16 at 2001200 140 – – – 2100 200 270 400 1830 190 1460 N12 at 400 N12 at 2001000 140 – – – 1400 200 270 400 1130 190 1260 N12 at 400 N12 at 200800 140 – – – 1200 200 200 300 1000 190 260 N12 at 400 N12 at 200


26




3000 190 1800 290 1200 3500 350 300 380 3200 340 1810 N16 at 400 N16 at 4002800 190 1800 290 1000 3100 350 300 350 2800 340 1610 N16 at 400 N16 at 400


1600 190 – – – 1500 250 200 200 1300 240 710 N16 at 400 N16 at 4001400 190 – – – 1000 250 200 180 800 240 510 N16 at 400 N16 at 4001200 140 – – – 1100 200 150 150 950 190 460 N12 at 400 N12 at 4001000 140 – – – 1400 200 – – – 190 360 N12 at 400 N12 at 400800 140 – – – 800 200 – – – 190 160 N12 at 400 N12 at 400


1000 140 – – – 2600 200 150 130 2430 190 2450 N12 at 400 N12 at 400800 140 – – – 1900 200 150 100 1750 190 1660 N12 at 400 N12 at 400


1000 140 – – – 4200 200 150 130 4050 190 3960 N12 at 400 N12 at 400800 140 – – – 3200 200 150 100 3050 190 2960 N12 at 400 N12 at 400


27




2000 190 1400 290 600 1900 350 300 400 1300 340 1710 N16 at 400 N16 at 2001800 190 – – – 2000 250 270 400 1730 240 1510 N16 at 400 N16 at 200



2000 190 1400 290 600 3700 350 300 400 3400 340 2210 N16 at 400 N16 at 4001800 190 – – – 3800 250 270 400 3530 240 1910 N16 at 400 N16 at 400



1000 140 – – – 2400 200 270 400 2130 190 1360 N12 at 400 N12 at 400800 140 – – – 2000 200 200 300 1800 190 1060 N12 at 400 N12 at 400

Appendix B Design Example

The following example demonstrates the methodused to design a typical reinforced concretemasonry cantilever retaining wall in accordance withAS 4678 and the design considerations set out inthis Guide. It may also be used to check thesuitability of commercially-available design softwarethat is intended to be based on AS 4678 and on thisGuide.

1 Wall DetailsWall slope

ω = 0°

Backfill slopeβ = 15.0°

Height of stem above soil in front of wallH’ = 3.6 m

Live load surchargeql = 5.0 kPa

Dead load surchargeqd = 0 kPa

Height of water table from top of drainage layerHw = 0 m

Limits for determining Structure Classification

θtm =2ω + φ

3

=(2 x 0°) + 35°

3= 11.7°

θb = θtf

=2ω + 3φ

5

=(2 x 0°) + (3 x 35°)

5= 21.0°

NOTE: Structures beyond the base limit or beyond thetop limits are unlikely to be affected by, or have anaffect upon, the structure clasification

There are no major structures located within the limits.

Structure failure results moderate damage.Structure Classification = 2

Reduction factorΦn = 1.0

2 Earthquake ConsiderationsLocation

Sydney

Acceleration coefficienta = 0.08

Soil profileNot more than 30 m of firm clay

Site factors = 1.0

Earthquake design category = Ber∴ Design for static loads without further

specific analysis

3 Load FactorsLoad factor on overturning dead loads

Gdo = 1.25

Load factor on overturning live loadsGlo = 1.5

Load factor on resisting dead loadsGdr = 0.8

Load factor on resisting live loadsGlr = 0.0

4 Infill Soil PropertiesSoil description

Controlled crushed sandstone or gravel fillsClass 2 controlled fill

Characteristic internal angle of frictionφi = 35°

Design uncertainity factor for frictionΦuφi = 0.90

Design angle of frictionφ*i = tan-1[(tan φi)Φuφi]

= tan-1[(tan 35°)0.90]= 32.2°

Characteristic cohesionci = 3.0 kPa

Design uncertainty factor for cohesionΦuci = 0.75

Design cohesionc*i = ci Φuci

= 3.0 x 0.75= 2.3 kPa Assume zero for design

Soil densityγ*i = 18.6 kN/m3

Design external friction angleδ*i = 2/3 φ*i

= 2 x 32.23

= 21.5°


28

θb

θtf

θtm

Baselimit

Top limit(dead load)

Top limit (live load)

ω

5 Retained Soil PropertiesSoil description

Stiff sandy clayInsitu

Characteristic internal angle of frictionφr = 29°

Design uncertainity factor for frictionΦuφr = 0.85

Design angle of frictionφ*r = tan-1[(tan φi)Φuφr]

= tan-1[(tan 29°)0.85]= 25.2°

Characteristic cohesioncr = 5.0 kPa

Design uncertainty factor for cohesionΦucr = 0.70

Design cohesionc*r = cr Φucr

= 5.0 x 0.70= 3.5 kPa Assume zero for design

Soil densityγ*r = 19.6 kN/m3

Design external friction angle(soil to soil interface)

δ*r = φ*r

= 25.2°

6 Foundation Soil PropertiesSoil description

Reconstruct the foundation to improve properties.Use crushed sandstone fillControlled fill, Class 2

Characteristic internal angle of frictionφf = 35°

Design uncertainity factor for frictionΦuφf = 0.90

Design angle of frictionφ*f = tan-1[(tan φf)Φuφf]

= tan-1[(tan 35°)0.90]= 32.2°

Characteristic cohesioncf = 3.0 kPa

Design uncertainty factor for cohesionΦucf = 0.75

Design cohesionc*f = cf Φucf

= 3.0 x 0.75= 2.3 kPa for bearing and zero for sliding

Soil densityγ*f = 18.6 kN/m3

7 Retaining Wall Stem and BaseArrangement

8 Masonry PropertiesBlock height

hu = 190 mm

Mortar joint thicknesstj = 10 mm

Height ratiohu =

190tj 10

= 19.0

Compressive strength factorkh = 1.3 AS 3700 Table 3.2

Masonry factor for face-shell-bedded concrete unitskm = 1.6 AS 3700 Table 3.1

Mortar typeM3 (1:5 + water thickener)

Characteristic unconfined unit strengthf’uc = 15 MPa

Characteristic masonry strength for 76-mm-highunits

f’mb = km√f’uc AS 3700 Clause 3.3.2(a)(i)

= 1.6√15= 6.2 MPa

Characteristic unconfined masonry strengthf’m = kh f’mb AS 3700 Clause 3.3.2(a)(i)

= 1.3 x 6.2= 8.06 MPa


29

Thin stem

Thick stem

Base

80 190

ω ≈ 1.43° (1 in 40)

Use 0° for design

Block properties:

Face-shellthickness,ts1 = 30 mm

Block coretaper,tt1 = 3 mm

B1 = 3400

B2 =1000 B3 = 460

B4 =1000 T1 =190

T2 =460

B6 = 2210

B7 = 1940

B5 = 1940

H9

= 4

792

H5

= 4

600

H12

= 5

192

H4

= 4

200

H3

= 4

00 H2

= 5

00H

6 =

370

0

H1

= 3

600

H10

= 5

92H

11 =

100

0

H8

= 1

900

H13

= 1

00

H7

= 1

800

β = 15°

9 Thin-Stem StrengthsBlockwork width

T1 = 190 mm

Face-shell thicknessts1 = 30 mm

Block core tapertt1 = 3 mm

Steel reinforcementN16 bars at 400-mm centres

Reinforcement strengthfsy = 500 MPa

Diameter of reinforcementDia = 16 mm

Required clear cover to steel from face shellcc.req = Max (20 mm aggregate, 15 mm cover)

AS 3700 Table 10.7.2.5= 20 mm AS 3700 Table 5.1

Required cover to steel centrelinecreq = cc.req + Dia/2 + tt1 + ts1

= 20 + 16/2 + 3 + 30= 61 mm

Specify cover to steel centrelinec = 65 mm (ie from rear face of block)

> 61 mm OK

Effective depthd = T1 - c

= 190 - 65= 125 mm

Capacity reduction factorφ = 0.75 AS 3700 Table 4.1

Determine out-of-plane shear capacity for thin-stemsection:

Characteristic shear strengthf'ms = 0.35 MPa (at interface) AS 3700 Cl 3.3.4(d)f'vm = 0.35 MPa AS 3700 Cl 8.6.3

Width of webbw = 1000 mm

Design shear strengthfvs = 17.5 MPa AS 3700 Cl 8.6.3

Cross-sectional area of reinforcement

Ast = 200 x 1000

400= 500 mm2/m

< 0.02 bw d AS 3700 Cl 8.6.3= 0.02 x 1000 x 125= 2500 mm2 OK

Cross-sectional area and spacing of shear reinf.Asv = 0 (no stirrups) S = NA

Out-of-plane shear capacity AS 3700 Cl 8.6.3

Vcap = min{ø[f'vm bw d + fvs Ast + fsyAsv d

] orS

4ø f'vm bw d}

= min{0.75[(0.35x1000x125)+ (17.5x500)+0]

1000

or 4 x 0.75 x 0.35x1000x125

}1000= min{39.4 or 131.3}= 39.4 kN/m

Design area of reinforcementAsd = Ast

= 500 mm2

< (0.29) 1.3 f'm b d

AS 3700 Cl 8.5fsy

= 0.29 x 1.3 x 8.06 x 1000 x 125

500

= 759 mm2 OK

> 0.0013 b d AS 3700 Cl 8.5= 0.0013 x 1000 x 125= 163 mm2 OK

Moment capacity AS 3700 Cl 8.5

Mcap = ø fsy Asd d 1 - 0.6 fsy Asd

1.3 f'm b d

= 0.75 x 500 x 500 x 125 x

1 - 0.6 x 500 x 500

x 10-6

1.3 x 8.06 x 1000 x 125

= 20.8 kN.m/m

10 Thick-Stem StrengthsBlockwork width

T2 = 460 mm

Face-shell thicknessts2 = 30 mm

Block core tapertt2 = 3 mm


Diameter of ReinforcementDia = 20 mm


Required clear cover to steel from face shellcc.req = Max (20 mm aggregate, 15 mm cover)

AS 3700 Table 10.7.2.5= 20 mm AS 3700 Table 5.1

Required cover to steel centrelinecreq = cc.req + Dia/2 + tt2 + ts2

= 20 + 20/2 + 3 + 30= 63 mm

Specify cover to steel centrelinec = 95 mm (ie in centre of rear block)

> 63 mm OK


30

Effective depthd = T2 - c

= 460 - 95= 365 mm

Capacity reduction factorφ = 0.75 AS 3700 Table 4.1

Determine out-of-plane shear capacity forthick-stem section:

Characteristic shear strengthf'ms = 0.35 MPa (at interface) AS 3700 Cl 3.3.4(d)f'vm = 0.35 MPa AS 3700 Cl 8.6.3

Width of webbw = 1000 mm

Design shear strengthfvs = 17.5 MPa AS 3700 Cl 8.6.3

Cross-sectional area of reinforcement

Ast = 310 x 1000

400= 775 mm2/m

< 0.02 bw d AS 3700 Cl 8.6.3= 0.02 x 1000 x 125= 2500 mm2 OK

Cross-sectional area and spacing of shear reinf.Asv = 0 (no stirrups) S = NA

Out-of-plane shear capacity AS 3700 Cl 8.6.3

Vcap = min{ø[f'vm bw d + fvs Ast + fsyAsv d

] orS

4ø f'vm bw d}

= min{0.75[(0.35x1000x365)+ (17.5x775)+0]

1000

or 4 x 0.75 x 0.35x1000x365

}1000= min{106.0 or 383.0}= 106.0 kN/m

Design area of reinforcementAsd = Ast

= 775 mm2

< (0.29) 1.3 f'm b d

AS 3700 Cl 8.5fsy

= 0.29 x 1.3 x 8.06 x 1000 x 365

500

= 2217 mm2 OK

Moment capacity AS 3700 Cl 8.5

Mcap = ø fsy Asd d 1 - 0.6 fsy Asd

1.3 f'm b d

= 0.75 x 500 x 775 x 365 x

1 - 0.6 x 500 x 775

x 10-6

1.3 x 8.06 x 1000 x 365

= 99.6 kN.m/m

11 Thick-stem/Thin-stem ConnectionAt the connection of thethick stem to the thin stem,there exists the possibilitythat the thin stem couldshear away. To prevent this,ties should be inserted,transferring the shear loadsdirectly into the block of thethick stem. use 1-N10 tie at400-mm centres.


Diameter of reinforcementDiatie = 10 mm

Cross-sectional area of tie

Atie = 78.5 x 1000

400= 196 mm2/m

Capacity reduction factorφ = 0.75

Capacity of tieVtie.cap = φ fsy Atie

= 0.75 x 500 x 196

1000= 74 kN/m

12 Base StrengthsSatisfactory shear and bending moment capacitycan be achieved by using the same reinforcementin the base as is required in the stem and ensuringthe depth of the section of the base is greater thanthe thicknes of the stem, provided reinforcementlimits are observed. The capacity can be checkedas follows.

Base depthH2 = 500 mm

> 460 mm (thick stem) OK



Diameter of reinforcementDia = 20 mm

Surface of member in contact withnon-aggressive soilExposure classification A2 AS 3600 Table 4.3

Concrete strength gradef’c = 25 MPa AS 3600 Clause 4.4

Characteristic flexural tensile strengthf’cf = 0.6 (f’c)0.5 AS 3600 Clause 6.1.1.3

= 0.6 x 250.5

= 3.0 MPa

Footing will be cast against ground without membraneRequired clear cover to steel from face of concrete

cc.eq = 30 + 20 AS 3600 Tables 4.10.3.2, 4.10.3.3= 50 mm


31

Potential crack

Thin stem

Thick stem

Required cover to steel centrelinecreq = cc.req + Dia/2

= 50 + 20/2= 60 mm

Specified cover to steel centrelinec = 70 mm (Allows for some variation in placing)

> 60 mm OK

Effective depthd = H2 - c

= 500 - 70= 430 mm

Capacity-reduction factor for bendingφb = 0.8 AS 3600 Table 2.3

Capacity-reduction factor for shearφv = 0.7 AS 3600 Table 2.3

Area of tensile steel

Ast = 310 x 1000

400= 775 mm2/m

Tensile steel ratioAst =

775

b d 1000 x 430= 0.00180

≥ 0.22 (D/d)2 f’cf/fsy= 0.22 (500/430)2 3/500= 0.00179 OK

Shear reinforcementAsv = 0

Shear coefficientsβ1 = 1.1(1.6 - do/1000) AS 3600 Clause 8.2.7.1

= 1.1(1.6 - 430/1000)= 1.29

≥ 1.1

β2 = 1.0 AS 3600 Clause 8.2.7.1

β3 = 1.0 AS 3600 Clause 8.2.7.1

Ultimate shear strength excluding reinforcementAS 3600 Clause 8.2.7.1

Vuc = β1 β2 β3 bv doAst f’c 1/3

bv do

= 1.29 x 1.0 x 1.0 x 1000 x 430775 x 25 1/3 1

1000 x 430 1000

= 197 kNVus = 0 AS 3600 Clause 8.2.10

Shear capacityφVu = φ(Vuc + Vus) AS 3600 Clause 8.2.2

= 0.7(197 + 0)= 138 kN/m

Ratio of depth of assumed compression blockγ = 0.85 - 0.007(f’c - 28) AS 3600 Clause 8.1.2.2

= 0.85 - 0.007(25 - 28)= 0.87

> 0.65 OKUse moment capacity formulabased on 0.85

Bending ratio

q = Ast fsy AS 3600 Clause 8.1.2.2b d f’c

= 775 x 500

1000 x 430 x 25

= 0.0360Bending capacity

R C Design Handbook Clause 4.2.2*Mcap = φb f’c q(1 - q/1.7)b d2

= 0.8 x 25 x 0.036(1 -0.036

)1000 x 4302

1.7 106

= 130 kNm/m

13 Active Pressure on StemActive pressure coefficient of infill soil

Kai =cos2(φ*i + ω)

cos2(ω)cos(ω - δ*i) 1 + sin(φ*i + δ*i)sin(φ*i - β) 2

cos(ω - δ*i)cos(ω + β)

= cos2(32.2° + 0°)cos2(0°)cos(0° - 21.5°)

1 + sin(32.2° + 21.5°)sin(32.2° - 15°) 2

cos(0° - 21.5°)cos(0° + 15°)

= 0.335

14 Thin Stem DesignHeight of thin stem

H7 = 1.8 m

Horizontal active force due to surchargePqHi7 = Kai[(Gdo qd) + (Glo ql)]H7 cos (δ*i - ω)

= 0.335[(1.25 x 0) + (1.5 x 5.0)] 1.8 xcos (21.5° - 0°)

= 4.2 kN/m

Horizontal active force due to soilPsHi7 = Kai 0.5 Gdo γ*i H7

2 cos (δ*i - ω)

= 0.335 x 0.5 x 1.25 x 18.6 x (1.8)2 xcos (21.5° - 0°)

= 11.7 kN/m

Total horizontal forcePHi7 = PqHi7 + PsHi7

= 4.2 + 11.7= 15.9 kN/m

Maximum shearV*

7 = PHi7= 15.9 kN/m

< 39.4 kN/m (reinforced blockwork)< 74.0 kN/m (tie to thick stem)

Maximum bending moment

M*7 = PqHi7 x

H7 + PqHi7 x H7

2 3

= 4.2 x 1.8

+ 11.7 x 1.8

2 3

= 10.8 kN.m/m< 20.8 kN.m/m OK

*Reinforced Concrete Design Handbook, jointly

published by Cement and Concrete Association

of Australia and Standards Australia.


32


33

15 Thick Stem DesignHeight of thick stem

H6 = 3.7 m

Horizontal active force due to surchargePqHi6 = Kai[(Gdo qd) + (Glo ql)]H6 cos (δ*i - ω)

= 0.335[(1.25 x 0) + (1.5 x 5.0)] 3.7 xcos (21.5° - 0°)

= 8.6 kN/m

Horizontal active force due to soilPsHi6 = Kai 0.5 Gdo γ*i H6

2 cos (δ*i - ω)

= 0.335 x 0.5 x 1.25 x 18.6 x (3.7)2 xcos (21.5° - 0°)

= 49.6 kN/m

Total horizontal forcePHi6 = PqHi6 + PsHi6

= 8.6 + 49.6= 58.3 kN/m

Maximum shearV*

6 = PHi6= 58.3 kN/m

< 106.0 kN/m

Maximum bending moment

M*6 = PqHi6 x

H6 + PqHi6 x H6

2 3

= 8.6 x 3.7

+ 49.6 x 3.7

2 3

= 77.1 kN.m/m< 99.6 kN.m/m OK

16 Base DesignUpper-bound estimates of the shear force andbending moments in the heel of the base may becalculated as follows.

Upper-bound bending moment

M*base = M*

6

= 77.1 kNm/m

< 130 kNm/m OKUpper-bound shear force

V*base =

M*base

0.5 B5

= 77.1

0.5 x 1.940

= 79.51 kN/m< 138 kN/m OK

17 External StabilityHorizontal forces are calculated from the soilsurface at the back of the heel to the underside ofthe key. In this case, passive pressure will also becalculated in front of the base and key.

Consistent with the above assumption, the structuredown to the underside of the key is considered.Vertical forces include the soil under the base downto this level.

For the ultimate stability limit state, provided thefoundation reaction is within the base, the structurewill not overturn. However, errors in the calculationof the ultimate bearing reaction, and therefore, inthe position of the reaction, could lead to anoverestimation of the stability. Therefore, it isprudent to nominate a minimum distance from thebase of the toe to the reaction.

As a first check, one-third of the base may be used.That is, the centroid of an idealised rectangularfoundation reaction is within the middle third of thebase at ultimate limit state. This is moreconservative than the same requirement imposed atworking stress loads.

X’ = 0.33 B1= 0.33 x 3.4= 1.122 m

18 Active Pressure on StructureActive pressure coefficient

Kar =cos2(φ*r + ω)

cos2(ω)cos(ω - δ*r) 1 + sin(φ*r + δ*r)sin(φ*r - β) 2

cos(ω - δ*r)cos(ω + β)

= cos2(25.2° + 0°)cos2(0°)cos(0° - 25.2°)

1 + sin(25.2° + 25.2°)sin(25.2° - 15°) 2

cos(0° - 25.2°)cos(0° + 15°)

= 0.464

19 Passive Pressure on StructurePassive pressure coefficient

Kpf =1 + sin φ*f1 - sin φ*f

=1 + sin 32.2°

1 - sin 32.2°

= 3.28

20 Horizontal Active Force due tosurcharge

Horizontal active force due to surchargePqH = Kar[(Gdo qd) + (Glo ql)]H12 cos (δ*r - ω)

= 0.464[(1.25 x 0) + (1.5 x 5.0)] 5.192 xcos (25.2° - 0°)

= 16.4 kN/m

Lever arm of horizontal surcharge force above base

yqH=H12

2

=5.192

2

= 2.596 m


34

Overturning moment due to surchargeMqHO = PqH yqH

= 16.4 x 2.596= 42.4 kN.m/m

21 Horizontal Active Force due to SoilHorizontal active force due to soil

PsH = Kar 0.5 Gdo γ*r H122 cos (δ*r - ω)

= 0.464 x 0.5 x 1.25 x 19.6 x 5.1922 xcos (25.2° - 0°)

= 138.7 kN/m

Lever arm of horizontal soil force above base

ysH =H12

3

=5.192

3

= 1.731 mOverturning moment due to soil

MsHO = PsH ysH= 138.7 x 1.731= 240.0 kN.m/m

22 Horizontal Passive ForcePassive force on base and key

Pp(k+b)H = Kpf 0.5 Gdo γ*f H112

= 3.28 x 0.5 x 0.8 x 18.6 x 1.02

= 24.4 kN/m

Lever arm of passive horizontal soil force abovebase

ypHR =H11

3

=1.0

3

= 0.333 mRestoring moment due to passive horizontal soilforce

MpHR = Pp(k+b)H ypHR= 24.4 x .0333= 8.1 kN.m/m

23 Weight of Thin StemWeight of thin stem

P1V = GdR γmasonry H7 T1= 0.8 x 23.0 x 1.8 x 0.19= 6.3 kN/m

Lever arm on weight of thin stemX1V = B4 + T1/2 - X’

= 1.0 + 0.19/2 - 1.122= - 0.027 m

Restoring moment due to weight of thin stemM1R= P1V X1V

= 6.3 x (-0.027)= - 0.2 kN.m/m

24 Weight of Thick StemWeight of thick stem

P2V = GdR γmasonry H8 T2= 0.8 x 23.0 x 1.9 x 0.46= 16.1 kN/m

Lever arm on weight of thick stemX2V = B4 + T2/2 - X’

= 1.0 + 0.46/2 - 1.122= 0.108 m

Restoring moment due to weight of thick stemM2R= P2V X2V

= 16.1 x 0.108= 1.7 kN.m/m

25 Weight of Soil above Thick StemWeight of soil above thick stem

P3V = GdR γ*i H7(T2 - T1)= 0.8 x 18.6 x 1.8(0.46 - 0.19)= 7.2 kN/m

Lever arm on weight of soil above thick stemX3V = B4 + T1 +(T2 - T1)/2 - X’

= 1.0 + 0.19 + (0.46 - 0.19)/2 - 1.122= 0.203 m

Restoring moment due to weight of soil above thickstem

M3R= P3V X3V= 7.2 x 0.203= 1.5 kN.m/m

26 Weight of Soil in Batter(Above Top of Wall)

Weight of soil in batterP4V = GdR γ*i 0.5 B6 H10

= 0.8 x 18.6 x 0.5 x 2.21 x 0.592= 9.7 kN/m

Lever arm on weight of soil in batterX4V = B4 + T1 + (2 B6)/3 - X’

= 1.0 + 0.19 + (2 x 2.21)/3 - 1.122= 1.541 m

Restoring moment due to weight of soil in batterM4R= P4V X4V

= 9.7 x 1.541= 15.0 kN.m/m

27 Weight of Soil above HeelWeight of soil above heel

P5V = GdR γ*i B7 H6= 0.8 x 18.6 x 1.94 x 3.7= 106.8 kN/m

Lever arm on weight of soil in batterX5V = B4 + T2 + B7/2 - X’

= 1.0 + 0.46 + 1.94/2 - 1.122= 1.308 m

Restoring moment due to weight of soil in batterM5R= P5V X5V

= 106.8 x 1.308= 139.7 kN.m/m


35

28 Weight of BaseWeight of base

P6V = GdR γ*c B1 H2= 0.8 x 25.0 x 3.4 x 0.5= 34.0 kN/m

Lever arm on weight of baseX6V = B1/2 - X’

= 3.4/2 - 1.122= 0.578 m

Restoring moment due to weight of baseM6R= P6V X6V

= 34.0 x 0.578= 19.7 kN.m/m

29 Weight of KeyWeight of key

P7V = GdR γ*c B3 H2= 0.8 x 25.0 x 0.46 x 0.4= 3.7 kN/m

Lever arm on weight of keyX7V = B2 + B3/2 - X’

= 1.0 + 0.46/2 - 1.122= 0.108 m

Restoring moment due to weight of keyM7R= P7V X7V

= 3.7 x 0.108= 0.4 kN.m/m

30 Vertical Component of Soil Frictionat Heel

To calculate the vertical component of soil friction atthe heel, the factored horizontal force component ismultiplied by tan(δ*r - ω)

That is, this force effectively has a load factor of1.25 applied, even though it has a restoring effect.

Vertical component of soil friction at heelP8V = (PsH + PqH) tan(δ*r - ω)

= (138.7 + 16.4) tan (25.2° - 0°)= 73.0 kN/m

Lever arm of vertical component of soil frictionat heel

X8V = B1 - X’= 3.4 - 1.122= 2.278 m

Restoring moment due to vertical component of soilfriction at heel

M8R= P8V X8V= 73.0 x 2.278= 166.3 kN.m/m

31 Weight of Soil Under BaseWeight of soil under base

P9V = GdR γ*f H3(B1 - B3)= 0.8 x 18.6 x 0.4(3.4 - 0.46)= 17.5 kN/m

The soil under the base exerts a vertical pressure onthe foundation at the level of the key and, therefore,must be included in the total vertical load.

However, this soil can not exert a resisting momentand, therefore, must be neglected for stabilitypurposes.

32 Vertical Surcharge on HeelVertical surcharge on heel

P10v = (Gdo qd + Glo ql)(B1 - T1 - B4)= [(1.25 x 0) + (1.5 x 0)](3.4 - 0.19 - 1.0)= 0 kN/m

or

P10v = [(1.25 x 0) + (1.5 x 5.0)](3.4 - 0.19 - 1.0)= 16.6 kN/m

33 Base SlidingAssume rough base-to-soil interface(Provided a key is used or if the interface betweenthe soil and the concrete of the base is not smooth,a friction angle of φ may be used. Otherwise, anangle of δ would be appropriate)

Friction resistancePfr = Φn(P1V + P2V + P3V + P4V + P5V + P6V + P71V +

P8V + P9V) tan φ*f= 1.0(6.3 + 16.1 + 7.2 + 9.7 + 106.8 + 34.0 +

3.7 + 73.0 + 17.5) tan 32.2°= 172.9 kN/m

Base adhesionPba = Φn B1 C*a

= 1.0 x 3.4 x 0= 0 kN/m

Passive force in front of base and keyPpH = Φn Pp(k+b)H

= 1.0 x 24.4= 24.4 kN/m

Total sliding resistancePsR = Pfr + Pba + PpH

= 172.9 + 0 + 24.4= 197 kN/m

Sliding forcePbH = PqH + PsH

= 16.4 + 138.7= 155 kN/m

< 197 kN/m OK

Sliding should also be checked at the interface ofany soil strata beneath the structure.

34 OverturningOverturning has been checked about a point that isone-third of the base width from the toe and at thelevel of the underside of the key.

Resisting momentsMR = Φn(M1R + M2R + M3R + M4R + M5R + M6R +

M7R + M8R + MpHR)= 1.0(-0.2 + 1.7 + 1.5 + 15.0 + 139.7 + 19.7 +

0.4 + 166.3 + 8.1)= 352 kNm/m

Overturning momentsMO = MqHO + MsHO

= 42.4 + 240.0= 282 kNm/m

< 352 kNm/m OK

35 Bearing at Underside of KeyDepth of embedment, He = H11 = 1.0 mActual width of base, B = B1 = 3.4 m

Ratio of horizontal loads to vertical loads(Check both maximum and minimum vertical loads)PH =

PqH + PsH

PV P10V + (P1V + P2V + P3V + P4V + P5V + P6V + P7V +P8V + P9V)

= 16.4 + 138.7 0 + (6.3 + 16.1 + 7.2 + 9.7 + 106.8 + 34.0 +

3.7 + 73.0 + 17.5)= 0.565

or

PH =16.4 + 138.7

PV 16.6 + (6.3 + 16.1 + 7.2 + 9.7 + 106.8 +34.0 + 3.7 + 73.0 + 17.5)1.25/0.8

= 0.348

Eccentricity

e =B

- X’ - MR - MO

2 PV

= 3.4 - 1.122 -

352 - 2822 274

= 0.323

or

e = 3.4 - 1.122 -

372 - 2822 445

= 0.377

Bearing widthLB = B - 2e

= 3.4 - (2 x 0.323)= 2.753

or

LB = 3.4 - (2 x 0.377)= 2.645

Bearing capacity factorsNq = eπtanφ*f tan2(π/4 + φ*f/2)

= eπtan32.2° tan2(π/4 + 32.2°/2)= 23.8

Nc = (Nq - 1)cot φ*f= (23.8 - 1)cot 32.2°= 36.2

Nγ = 2(Nq + 1)tan φ*f= 2(23.8 + 1)tan 32.2°= 31.2

ζq = 1.0

ζqi = 1 - PH

2

PV + LB c*f cot φ*f

= 1 - 155 2

274 + 2.753 x 2.3 x cot 32.2°

= 0.23

or

ζqi = 1 - 155 2

445 + 2.858 x 2.3 x cot 32.2°

= 0.45

ζqt = [1 - α tan φ*f]2

= [1 - 0 tan 32.2°]2

= 1.0

ζc = 1.0

ζci = ζqi - 1 - ζqi

Nc tan φ*f

= 0.23 - 1 - 0.23 36.2 x tan 32.2°

= 0.20

or

ζci = 0.45 - 1 - 0.45

36.2 x tan 32.2°

= 0.43

ζct = ζqt - 1 - ζqt

Nc tan φ*f

= 1.0 - 1 - 1.0 36.2 x tan 32.2°

= 1.0

ζγ = 1.0

ζγi = 1 - PH

3

PV + LB c*f cot φ*f

= 1 - 155 3

274 + 2.753 x 2.3 x cot 32.2°

= 0.11

or

ζγi = 1 - 155 3

445 + 2.858 x 2.3 x cot 32.2°

= 0.30

ζγt = [1 - α tan φ*f]2

= [1 - 0 tan 32.2°]2

= 1.0

Average bearing strength capacityPVcap= Φn LB[(c*f Nc ζc ζci ζct) +

(γ*f He Nq ζq ζqi ζqt) + (0.5 γ*f B Nγ ζγ ζγi ζγt)]= 639 kN/m

or

PVcap= 1405 kN/m

Applied vertical forcePV= 274 kN/m

< 639 kN/m OK

or

PV= 445 kN/m< 1405 kN/m OK


36


37

APPENDIX C Site Investigation

SITE INVESTIGATION Date:

Reportprepared by:

Client:

Project:

Location:

Use for which retaining wall is intended:

Proximity of other structures and loads to the face of the retaining wall:

Structure or load Distance (m)

Distance of live loads from top of wall

Distance of dead loads from top of wall

Distance of other structures from base of wall

Structure classification:For guidance refer AS 4678, Table 1.1Structure Classification Examples1 Where failure would result in significant damage or risk to life2 Where failure would result in moderate damage and loss of services3 Where failure would result in minimal damage and loss of access

Required design life:

For guidance refer AS 4678, Table 3.1Type of Structure Design life (years)Temporary site works 5Mine structures 10Industrial structures 30River and marine structures 60Residential dwellings 60Minor public works 90Major public works 120

Required wall type:

Exposed height of retaining wall stem: m

Slope of wall: 1 horizontal in vertical

Slope of backfill: 1 vertical in horizontal

Specified surcharge loading (if any) or other loads: kPa


38

Soil Properties

EffectiveDensity internal angle Cohesion

Soil (kg/m3) of friction (°) (kPa) Soil type*

Insitu foundation

Imported foundation material

Insitu retained soil

Infill soil

* Please indicate the appropriate type(s) and add any other notes.

Hard rock, sandstone, gravel, sand, silty sand, clayey sand, stiff clay, weak clay, other

Are soil strength tests required? (yes/no)

Is there ground water seepage present? Now ( yes/no ) After heavy rain (yes/no)

If yes, how much?

Is it practical to install subsurface drainage (yes/no) and surface drainage (yes/no)?

How will the drainage system affect the site?

What is the effect of excavation or filling?

Are there obvious global stability problems? (yes/no)

What is the effect of ground movement?

General description of site topography(Sketch, site plan, and photographs where possible to be attached).


39

APPENDIX DConstruction Specification

SupervisionThe Contractor shall ensure that the work isperformed and directly supervised by appropriately-experienced personnel.

Quality AssuranceSuppliers and contractors shall provide assuranceof the quality of all goods, materials and services tobe provided. The following are deemed to meet thisrequirement:■ a quality assurance system complying with

AS/NZS ISO 9001, or■ a quality control system approved by the Builder.

Australian StandardsAll components and installation shall comply withthe Building Code of Australia (BCA) and therelevant Australian Standards, including AS 4678,AS 3700 and AS 3600 and the standards referred totherein.

Safety and Protection of Existing StructuresAll excavations shall be carried out in a safemanner in accordance with the relevant regulations,to prevent collapse that may endanger life orproperty.

In the absence regulations to the contrary, thefollowing may be applied, where:■ excavation is performed and remains open only

in dry weather,■ there is no significant ground water seepage,■ the excavation remains open for no longer than

two weeks,■ the back slope of the natural ground does not

exceed 1 vertical in 6 horizontal, ■ bedding planes do not slope towards the cut,

and ■ there are no structures founded within a zone of

influence defined by a line from the toe of the cutat 30° for cohesionless material and 45° for othermaterial.

In all other cases, the advice of the Engineer shallbe sought.

Adjacent structures must be founded either beyondor below the zone of influence. Where there is riskof global slip around a slip plane encompassing theproposed retaining wall or other structures, or wherethere is risk of inundation by ground water orsurface water, retaining wall construction shall notproceed until remedial action has been carried out.

Foundation MaterialFoundation material shall be uniform and of the typeshown on the drawings.

Preparation of Foundation MaterialWhere there are significant variations of foundationmaterial or compaction, soft spots or where there isponding of ground water, the material shall beremoved, replaced and compacted in layers notexceeding 150 mm at a moisture content within 2%of Optimum Moisture Content (OMC) to achieve95% Standard Proctor density.

Trenches and footing excavations shall bedewatered and cleaned prior to placement ofdrainage material or footings such that no softenedor loosened material remains. If necessary placeand compact foundation material in layers notexceeding 150 mm to make up levels. The levelsbeneath the wall shall not be made up with beddingsand or other poorly graded granular material thatmay permit ground water to permeate under thebase of the retaining wall, except where drainagematerial is specified and an adequate drainagesystem is designed.

ConcreteConcrete in the footings shall comply with AS 3600,strength grade N20 and maximum aggregate size of20 mm. Concrete shall be subject to plant controltesting.

ReinforcementAll reinforcement shall comply with AS/NZS 4671and shall be a minimum of Grade N500.

Positioning ReinforcementStarter bars shall be tied into position to provide thespecified lap above the top surface of the footing.The starter bars shall be held in position by a timbermember and controlled within a tolerance of ± 5 mmthrough the wall and ± 50 mm along the wall. Barchairs shall be placed at 1 m centres both ways togive the following clear cover. Chair bases shall beused to prevent sinking of the chairs. Unlessspecified otherwise on the drawings, structural lapsand cover shall be as follows.

Required Cover:

40 mm in concrete in contact with unprotectedground

40 mm in concrete exposed externally

30 mm to a sealed vapour barrier

20 mm to an internal surface

MaximumMaximum permissibleheight of cut unpropped batter

Natural material (m) Vert : horiz

Stable rock, sandstone, firm 0 – 3.2 1 : 0.4shale etc where beddingplanes do not slope towards Over 3.2 Seek advice of the excavation engineer

Materials with both 0 – 2.6 1 : 0.8significant cohesion andfriction in its undisturbed Over 2.6 Seek advice ofnatural compacted state engineer

Cohesive soils, 0 – 2.0 1 : 1.2eg clay, silts Over 2.0 Seek advice of

engineer

Cohesionless soils, 0 – 1.4 1 : 1.6eg Loose gravel, sand Over 1.4 Seek advice of

engineer


40

Laps shall comply with AS 3600, and shall be notless than:

Reinforcement Required Laps

Bars 500 mm

Fabric 2 cross wires overlapping

Trench mesh 500 mm

Two N12 corner bars, 1.0 m long, shall be placed atall re-entrant corners.

Placing and Finishing ConcreteUnless noted otherwise on the drawings, reinforcedconcrete footings for retaining walls shall include alevel concrete hob (or upstand), through whichvertical starter bars are placed and on which themasonry is built. Horizontal 50-mm-diameter weepholes shall pass through the hob at 1.2 m maximumcentres.

All concrete shall be compacted by immersionvibrator.

All concrete shall be cured using a sprayed curingcompound.

Concrete surfaces shall be finished as noted below,unless specified otherwise.■ Horizontal surfaces exposed in the completed

structure – fine-broomed steel float.■ Horizontal surfaces not exposed in the

completed structure – wood float.■ Vertical surfaces exposed in the completed

structure – rubbed back to fill all voids andprovide smooth surface.

■ Vertical surfaces not exposed in the completedstructure – off-form finish.

Concrete Blocks for Reinforced MasonryUnless specified otherwise, masonry units shallcomply with AS 4455 and the followingrequirements:■ Dimensional category DW4.

■ General purpose salt attack resistance grade(except where exposed grade is required).

■ Minimum characteristic compressive strength of10 MPa (unconfined value).

■ Colour and texture shall be within an agreedrange

■ Concrete blocks for reinforced masonry shallhave:

– maximum permeability of 2 mm/minute;

– efflorescence potential not more than slight;

– characteristic lateral modulus of ruptureof 0.8 MPa;

– H-Block or Double-U configuration;

– If blocks with webs flush with the endsare to be used, horizontal reinforcementshall be suspended above the webs on15-mm mortar pack on the centre webonly.

MortarCement shall be Type GP portland cementcomplying with AS 3972 unless specified otherwise.

Lime shall be hydrated building lime complying withAS 1672.1 unless specified otherwise.

Water thickeners shall be methyl-cellulose based.

Sand shall be clean sharp and free from salts,vegetable matter and impurities. It shall conform toAS 2758.1 except that the following grading shallapply:

Sieve Percent Passing

4.76 mm 95 – 1002.36 mm 95 – 100

1.18 mm 60 – 100

600 µm 30 – 100

300 µm 10 – 50

150 µm 0 – 10

75 µm 0 – 4

Fineness modulus 1.5 – 2.8

Mortar shall consist of the following:■ Type M3 – For general applications

(except where Type M4 is required)■ Preferred – 1 part Type GP cement, 5 parts sand

plus water thickener■ Alternative – 1 part Type GP cement, 1 part lime,

6 parts sand

GroutConcrete grout shall have a minimum portlandcement content of 300 kg/m3, a maximumaggregate size of 10 mm, sufficient slump tocompletely fill the cores and minimum compressivecylinder strength of 20 MPa.

Construction of Reinforced Masonry StemThe first course of a reinforced masonry wall shallconsist of clean-out blocks (with one face shell cutaway at the vertical reinforcement) to permit thesubsequent removal of debris and mortar fins. Theopening of the clean-out blocks shall face the soilembankment, except where there is insufficientaccess. The blocks shall be positioned to provide atleast 20-mm clear cover to the inside of the faceshell, allowing for shell taper. For N12, N16 and N20bars, the steel position through common blockworkshall be as follows:

Maximum Rear face Front faceWall face shell to vertical to verticalthickness plus taper bar centre bar centre(mm) (mm) (mm) (mm)

190 35 65 125

290 35 65 225

If using flush ended blocks, leave 10-mm weepholes between all clean-out blocks.


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Subsequent courses shall consist of H-Block orDouble-U Block. Horizontal reinforcement placedcentrally on the webs during the laying of theblockwork. If blocks with webs flush with the endsare to be used, horizontal reinforcement shall besuspended above the webs on 15-mm mortar packon the centre web only.

Mortar joints shall be 10 mm thick and shall beface-shell bedded and ironed (unless a flush joint isspecified for aesthetic reasons). Control joints shallbe built into the masonry at joints in the footing, atsignificant changes in wall profile or at centres notexceeding 16 m.

If the retaining wall consists of two leaves of cavityconstruction, suitable cavity ties shall be built in atcentres such that the wet grout pressure does notcause spreading of the cavity. Ties shall incorporate100 cogs at each end that shall bear snugly againstthe rebate in the blocks and shall be securely fixedby embedment in mortar. The followingcombinations are deemed to meet this requirement:

Maximumgrout height Tie/Maximum spacing(m) (Vertical x Horizontal)

1.8 R6 (Grade 250)/400 mm x 400 mm

Where a retaining wall consists of a single-leaf stemsupported by a cavity stem, links shall be providedin the first joint below the junction of cavity stemand single leaf stem to prevent widening of thecavity. The following reinforcement is deemed tomeet this requirement:

Maximum height of Requiredsingle-leaf stem (m) shear reinforcement

1.8 N10 at 400-mm centres

Debris and mortar fins shall be removed by roddingand hosing out the cores.

Vertical steel reinforcement shall be positionedtowards the rear of the cores to provide at least20 mm clear cover to the inside of the face shell,allowing for shell taper.

It shall be tied through clean-out openings with wireties to the steel starter bars and fixed in position atthe top of the wall by plastic clips before theplacing of any grout.

When cleaning out and tying of steel are complete,the opening shall be blanked off with a timber formsuitably propped to prevent movement.

Concrete grout shall be placed in the cores eitherby pumping or, for small projects, by bucket.Compact the grout so that there are no voids, usingeither a high frequency pencil vibrator or byrodding. (The main vertical bars shall not be movedto compact the grout.)

On completion of the grouting, capping blocks shallbe installed (if required) and any control jointsfinished.

Unless specified otherwise for reasons of aestheticsor by the client or architect, all construction shall bewithin the following tolerances:

Element

Facings and Footings andAspect Soil surface wall structures supports

Verticalposition ± 100mm ± 50mm ± 50mm

Horizontalposition – ± 50mm ± 50mm

Verticalalignment – ± 20mm in 3m ± 20mm in 3m

Horizontalalignment – ± 20mm in 3m ± 20mm in 3m

Drainage System The drainage system shall consist of:■ Weep holes through the impermeable wall facing.

■ A permeable drainage layer not less than 300 mmwide adjacent to the stem of the wall.

■ A 100-mm slotted PVC agricultural pipe withgeofabric sock, or equivalent system, draining to thestormwater system

Drainage PipeThe drainage pipe shall be a 100-mm diameterslotted PVC agricultural pipe with geofabric sock.

Drainage FillDrainage fill material shall be a nominal 10–20 mmGP (poorly-graded gravel) complying with thefollowing specified grading:

Sieve Percent Passing

26.5 mm 100

19.00 mm 70–100

13.20 mm 0–100

9.52 mm 0

Installing Drainage FillDrainage fill shall be placed around the drainagepipe and up the wall, to a minimum thickness of300 mm.

Installing the Drainage SystemThe drainage pipe shall be positioned in thedrainage fill at a minimum uniform grade of 1 in 100over a length not exceeding 15 m. It shall beconnected to the storm-water system at the lowerend of each run and shall drain positively away frombase of the retaining wall. The drainage pipe shallbe brought to the surface at the upper end of eachrun (to facilitate future flushing) capped and itsposition marked.

Bulk Fill MaterialBulk fill material shall be uniform and of the typeshown on the drawings. The maximum particle sizeis 100 mm. It is permissible to replace material of alower design type with properly-compacted materialof a higher design category.


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Installing Bulk Fill MaterialUnless required otherwise to support external loads,bulk filling material shall be placed and compactedbehind the drainage material in layers notexceeding 200 mm at a moisture content within 2%of Optimum Moisture Content (OMC) to achieve85% Standard Proctor density.

Surface Sealing MaterialThe material used to seal the surface of the fill shallbe compacted clay.

Installation of Surface Sealing Material andCatch DrainThe whole of the disturbed fill surface shall besealed and drained by compacting a layer ofsurface sealing material at least 150 mm thick andincorporating a 100 mm deep catch drain whichdrains to the site drainage system at a minimumslope of 1 in 100.

Inspections and TestsAll new work shall remain open until it has beeninspected and approved by the Engineer. Thefollowing inspections shall be performed.

Inspection Acceptance Hold/Item or product required criteria Witness

Footing dimensions:Width Spot check + 10%, - 2% HoldLength Spot check + 10%, - 2% HoldEdge forms Check all edges ± 20 mm Hold

Footing reinforcement:Grade Spot check markings As specified HoldDiameter Spot check diameter As specified HoldSpacing Spot check ± 10% HoldLaps Spot check ± 10% HoldCover Check chairs As specified Hold

Weep holes Spot check In position Hold

Concrete:Strength Spot check dockets Per AS 3600 WitnessCuring Spot check As specified Witness

Masonry units:Type Spot check As specified WitnessDimensions Spot check As specified WitnessStrength Spot check dockets As specified Witness

Mortar mix Spot check As specified Witness

Stem reinforcement:Grade Spot check markings As specified HoldDiameter Spot check diameter As specified HoldSpacing Spot check ± 10% WitnessLaps Spot check ± 10% WitnessCover Spot check As specified Hold

Concrete grout strength Spot check dockets As specified Witness

Cleaning Visual Per test panel Witness

Drainage system Flush pipes Positive 1:100 Hold

Granular fill Visual Grading Witness

Surface sealing andsurface drains Visual Per drawings Witness

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DESIGNED AND PRODUCED BY TECHMEDIA PUBLISHING PTY LTD +61 2 9477 7766

Concrete Masonry Association of AustraliaPO Box 572 St Leonards NSW 1590

Telephone 02 9903 7760

Facsimile 02 9437 9703

For details of masonry manufacturers, see CMAA Web Site:www.cmaa.com.au

ISBN 0 909407 49 5

CMAA MA51

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