HBM Platforms

8/11/2019 HBM Platforms

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Guidance on the use of HBM in workingplatforms

Project code: AGG79-06

Date of commencement of research: August 2005Finish date: March 2006

Written by:Hilary Skinner, Andrew Dunster, Rachel Harrex, Flavie Moulinier(BRE)

Published by:

The Waste & Resources Action ProgrammeThe Old Academy, 21 Horse Fair, Banbury, Oxon OX16 0AHTel: 01295 819900 Fax: 01295 819911 www.wrap.org.uk WRAP Business Helpline: Freephone: 0808 100 2040

August 2006

ISBN: 1-84405-285-0

Creating markets for recycled resources

R & D R e p o r t :

A g g r e g a

t e s


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Added value of using new industrial waste streams as secondary aggregates 1

Executive SummaryThis document is concerned with the use of hydraulically bound material (HBM) in working platforms used in a variety ofcivil engineering and building projects.

Stabilising land with the use of lime, cement or other binders to produce HBMs is now an extremely cost effectivemethod of converting weak soils into construction materials. Virtually any soils found on site can be improved using theHBM process for bulk fill or building applications. By using 'on site' soils or materials, construction can be carried outmore cheaply and quickly. In addition, use of site won materials can lead to significant savings in lorry movements andreductions in the environmental damage that this causes to the surrounding area. Ultimately, this also reduces the needfor quarrying and for landfill. Soil stabilisation therefore offers the potential for reduced environmental impacts otherwiseassociated with the extraction of primary aggregates, transportation of materials and landfilling.

A working platform provides a safe and sufficiently durable working surface from which construction plant, such as pilingrigs and cranes can operate. Platforms are essential when in situ soils give insufficient support, and good design canensure maximum efficiency of construction processes. Clear economic and environmental benefits can be derived fromthe use of platforms, particularly where increased use can be made of either site-won or recycled materials when platforms can be used and re-used for a variety of purposes throughout the construction process

when platforms can be re-used for permanent works.

Examples can be found of working platforms that are utilised many times through a construction life-cycle; they mayprovide support for the ground works plant, ensure minimal degradation or improve the subsoils, act as formwork forcasting pad foundations, provide a surface for steelwork erection and act as a structural element within a floor slab orpavement.

This is a guidance document for the use of recycled materials by means of HBM in the design, specification, installation,operation, maintenance and repair of a working platform and its subsequent reuse. Case studies can be found in

Appendix A.

This document has been written by BRE with extensive help from a project team comprising:Barry Chaddock (TRL)Paul Edwards (Scott Wilson Pavement Engineering)Nizar Ghazireh (Scott Wilson Pavement Engineering, formerly Tarmac)John Kennedy (JK Pavement Consulting)

The project team were also grateful for advice and comments made by the Steering Group, comprising the project teamtogether with:Chris Harnan and Mark Jones (O'Keefe Construction, on behalf of BRITPAVE)Tony Suckling (Stent Foundations, on behalf of FPS)John Barritt (WRAP)

Stabilisation works at the City of Manchester stadium (Britpave)


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Contents1. Introduction 3 2. Site conditions 8 3. Design 12 4. Platform Construction 18 5. Operation, Maintenance and Repair 21 6. Use for and interface with permanent works (formwork, blinding, foundation for pavements etc) 23 7. Standards and references 24

Appendix A Case studies 26

Note on scope of this document

The guidance seeks to avoid being over-prescriptive as this might limit the scope for innovation and the development ofcost-effective solutions. Hence the guide should be seen as an enabling document and not a code of practice .

The guidance cannot be relied upon to limit the liabilities or responsibilities of anyone involved in thedesign, specification, installation, operation, maintenance and repair of a working platform.

While the guidance describes good practice in general terms it cannot deal with every eventuality and site condition. Aformulation of good practice can only be of value where it is applied with careful supervision, control and monitoring ofthe platform on site under appropriate contractual arrangements. All parties have to exercise their own knowledge,experience and judgement.


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1. Introduction

1.1. Introduction Working platform definition Recycling, reuse and conservation of materials Scope of guidance

A working platform provides a safe and sufficiently durable working surface from which construction plant, such as pilingrigs and cranes can operate. The expression working platform is restricted in this guidance to ground-supported workingplatforms, including not only the platform itself but also the associated ramps and accesses.

A working platform supporting piling plant (Stent Foundations)

Platforms are essential when in situ soils give insufficient support, and good design can ensure maximum efficiency ofconstruction processes. Clear economic and environmental benefits can be derived from the use of platforms,particularly where use can be made of either site-won or recycled materials when platforms can be used and re-used for a variety of purposes throughout the construction process when platforms can be re-used for permanent works, and if not recycled for other site use.

Use of site won materials can lead to significant savings in lorry movements and the environmental damage that thiscauses to the surrounding area. This also reduces the need for quarrying and for landfill with their associatedenvironmental impacts.

Sites with soft, waterlogged subsoil before and after stabilisation (O'Keefe Soil Remediation)

Examples can be found of working platforms that are utilised many times through a construction life-cycle; they mayprovide support for the ground works plant, ensure minimal degradation or improve the subsoils, act as formwork for


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casting pad foundations, provide a surface for steelwork erection and act as a structural element within a floor slab orpavement. The case studies within this project (see project report) highlight the re-use of working platforms originallyplaced for the ground works plant later in the construction works and for permanent elements.

The guidance seeks to avoid being over-prescriptive as this might limit the scope for innovation and the development ofcost-effective solutions. Hence the guide should be seen as an enabling document and not a code of practice. Theguidance does not in any way limit the responsibilities of those parties involved in the design, specification, installation,operation, maintenance and repair of a working platform.

While the guidance describes good practice in general terms it cannot deal with every eventuality and site condition. Aformulation of good practice can only be of value where it is applied with careful supervision, control and monitoring ofthe platform on site under appropriate contractual arrangements. All parties have to exercise their own knowledge,experience and judgement.

1.2. Introduction to hydraulically bound materials (HBM) HBM CBM In situ and ex situ mixing

Stabilisation using hydraulic binders can improve the strength and durability of otherwise less suitable materials. Assuch, they offer the opportunity to produce working platforms that are sufficiently strong and durable that they can bereused many times during a construction project and could potentially form part of the permanent works.

This guidance covers the key issues related to working platforms constructed using stabilised materials. In this guidance,these comprise hydraulically bound materials (HBM), mixtures that set and harden by hydraulic reaction. HBMs includecement bound materials (CBM i.e. mixtures based on the fast setting and hardening characteristics of Portland Cement)and hydraulically bound mixtures based on slower setting and hardening binders made from industrial by-products suchas pulverised fuel ash (PFA) and granulated and ground granulated blastfurnace slag (GGBS) 1.

Throughout this report the added hydraulic component is known as a binder. Different binders can have slightly differenteffects that are dependent on the specific soil stabilised, and the correct mixture is part of the design process. HBMmixtures can rapidly dry out and significantly strengthen many weak soils.

HBM construction is well known and versatile in terms of availability of plant and materials. HBM can be produced byeither ex situ or in situ methods. Soils or granular materials can be mixed with hydraulic binder in a stationary mixing plant and the resulting HBM

placed and compacted by non-specialist plant. Plant for laying and compaction of HBM is similar to that required forlaying and compacting other paving materials such as unbound layers or bituminous bound products. The mixingprocess can be carried out using a "fixed plant" or "mobile plant". Both methods are classified as "ex situ".

Alternatively, surface soils on site can be mixed in-place with binders using specialist plant such as binder spreadersand rotavators. Compaction and grading can then take place. This offers significant advantages in the use ofindigenous materials instead of importing material to the site. This process is known as either the mix-in-place or"in situ" method. Often in situ mixing can be used on imported, otherwise unsuitable, material.

Throughout this guidance, the terms 'moisture content' and 'water content' should be considered interchangeable.

1 HBM materials cover a very wide range of granular and cohesive soils and binders, more information can be found insection 3.


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Ex situ stabilisation - batching plant (Sitebatch Technologies Ltd)

In situ stabilisation - specialist mixing plant (O' Keefe Soil Remediation)

1.3. Responsibilities Parties involved in provision of working platform for temporary and permanent works Responsibilities to be defined Use of appropriately qualified and experienced staff

A number of parties are likely to be involved in the design, installation, maintenance and repair of a working platform,including the client, the principal contractor, the designer of the permanent works and the contractors or subcontractorsfor whose work the platform is initially required. Table 1 gives an example of how this involvement may emerge during aconstruction project.


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Table 1. Example of parties involved in platform provision.

Often the information is incomplete at the time the platform is designed and installed. Whilst this should be avoided asfar as possible, the design for the platform should clearly state the basis on which the platform strength and durabilityhas been determined so that it can be checked against any subsequent use.

Contractual arrangements should ensure that the platform is adequately operated, maintained and, as necessary,repaired throughout its working life. The respective roles of the various parties should be clearly understood and theresponsibilities and liabilities of all parties should be defined in the relevant contract.

This guide does not extend or affect such responsibilities and liabilities.

1.4. Management procedures Installation Monitoring, maintenance and repair Operating requirements

Installation requirements need to be specified and a quality management process is required so that it can be certifiedthat the platform has been installed as specified. A check that the platform has reached the required strength will beneeded.

Operating requirements need to be specified so that the platform is not subjected to loads or other conditions whichwere not allowed for in the design. Procedures should be established to enforce these operating requirements andresponsibilities need to be clearly established.

Operation, maintenance and repair of the platform should ensure that it performs in accordance with the design over itsworking life. Systems should be in place to ensure that: monitoring of the platform takes place regularly; this should involve visual assessment of the performance of the

platform and operating plant and drainage regular maintenance can be carried out to keep a level surface or maintain drainage repairs are carried out when problems are identified and the platform reinstated after any excavation or damage.

1.5. Causes of platform failure Identification of hazards Localised problems Maintenance and repair Permanent works design

The objective of enhancing safety in use without excessive expenditure can only be achieved by identifying the mostsignificant hazards and determining where the primary risks lie. Otherwise there may be unnecessary expenditureimproving matters that are already satisfactory. Identification of the most significant hazards is a crucial first step in thedesign procedure. To date there is no known case of failure of an HBM platform in use.Table 2 shows the most likely theoretical causes of platform failure or observed poor performance other than inadequatedesign.

Table 2. Possible causes of platform failure or poor performanceIdentifier Possible cause

Excessive early age deformation Strength of HBM not yet mobilisedInsufficient or inappropriate binderInadequate thicknessPoor compaction

Local cracking and deformation Localised soft spot in subgrade

Poor repairPlatform of inadequate strength or thicknessEdge cracking Use of plant too close to edges of HBM platform

Party RequirementPermanent works engineer Define platform life, design for permanent works applicationPlatform designer Design and specify platformContractor or subcontractors Plant loading and other requirementsPlatform contractor Install to specification, notify any changes from specification

conditionsPrincipal contractor Overall responsibility under CDM


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Surface degradation Lack of maintenanceExcessive spraggingSurface finish not robust enough to withstand plant movementsInsufficient or inappropriate binderPoor compaction

Surface rutting Material strength inadequate with imposed loads

Waterlogging Lack of or inadequate drainage

The identification of local weaknesses in the subgrade and the prevention of weaknesses being formed in the platformare likely to do more to improve safety than refinement of design calculations. Other hazards such as open excavationsand the edges of the platform and access ramps should be identified and clearly marked.

Safe working areas around platform edges need to be clearly defined when the platform is ready to use(Geofirma)

HBMs have particular issues relating to: strength change with time water degradation repairs

These require careful consideration in order to ensure that the platform remains safe for use in both its temporarycondition and provides design performance for later temporary uses or permanent works.

Permanent works design must address performance and durability issues relating to the HBM; these may well bedifferent from those required for the temporary works.

Treated Untreated


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2. Site conditions2.1. Site investigation (SI) Involve a competent person at an early stage Importance of site appraisal Ground investigation for design parameters Weather dependency of near-surface ground Identification of weaker zones and hard spots Location of services

The investigation for and design of working platforms, including those constructed using HBM, are specialised processesand it is advisable to consult a competent person at an early stage.

The importance of a thorough appraisal of the entire site at an early stage cannot be over-emphasised. This shouldinclude a site inspection and it is particularly important to check for and report on the location of any weak and variableareas and drainage.

Appropriate and sufficient ground investigation is vital to ensure the provision of an adequate working platform.Information pertinent to the working platform design should be collected during the site investigation. The propertiesand variability of the near-surface ground are critical for the design and operation of the working platform. In contrast,for most construction projects it is the strength at greater depths that is important and, consequently, the near-surfacestrength may not have been adequately characterised in the site investigation for the construction project.

Historical records of site use, demolition records and the local knowledge of nearby residents may prove helpful andshould be included in the health and safety plan. Trial pits facilitate examination of the near surface ground, but carefulreinstatement is essential to avoid creating weaker zones in the subgrade. Characterisation of material types and theirproperties are required for HBM design purposes and for the overall platform design. The site investigation shouldprovide all the data that is required for both temporary and permanent works design and installation 2.

Localised weaker zones in the subgrade, including poorly backfilled excavations, can be critical for the performance ofthe platform and need to be identified. However, hard spots, such as old basement walls, can be just as hazardous asweaker zones. It is necessary that the whole of the platform area is examined. On a brownfield site, the records of thedemolition contractor on site reinstatement should be of assistance. The location of existing and abandoned servicesshould be carefully investigated. The likelihood of weaker areas needs to be assessed and groundwater conditionsevaluated. Variability in ground conditions needs to be identified.

Following the site investigation for the main works, it may be necessary to augment information obtained for theconstruction project with further investigation specifically for the working platform.

2.1.1. SI for HBM mix designThe primary purpose of the site investigation for HBM mix design is to locate, sample and identify the various types ofsoil such that sampling is representative of the platform area(s). The sampling regime and testing requirements mayalso depend on whether the working platform is to be reused later in the construction works or as permanent works.Where HBM is being considered for a given end use, for example in a pavement layer, there may be specificrequirements on the SI 3 (see also Section 2.1.3)

If in situ stabilisation of the soil is being considered, samples should relate to the area, site level and anticipated mixdepth which will be encountered so that tests of suitability can be made. This section gives a general guide to the SI thatmay be needed, in practice a competent person should specify and supervise the SI.

If soil is to be imported from offsite or elsewhere on site for ex situ stabilisation, samples should be taken at regularintervals to adequately characterise the materials to be used.

2 HD 25/94 Highways Agency DMRB Vol 7 Sect 2, Pt 2 indicates the scope of SI needed for pavements, note that this

may be too onerous for many temporary applications. This has now been superseded by IAN 25/06.3 HA74/00 DMRB Vol. 4 Pt. 6 Treatment of fill an capping materials using either lime or cement or both. Note that thisdoes not cover all HBM applications.


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A competent person with expertise in soil stabilisation may be able to estimate the type and likely volume of binderrequirement for some materials from a visual examination of the material; this can be carried out initially so that adecision can be made, on economic grounds, on whether to proceed with laboratory testing 4.

When assessing the suitability of materials (whether in situ or imported) for the production of HBM layers, generally theyfall into one of three categories:

1. No pre-treatment requiredMaterials that can be stabilised without preliminary treatment are predominantly granular materials, mixtures of granularand clayey soils where the clay content is low. Some uniformly graded granular materials may have a very high binderdemand in order to produce significant strength gain, but this strength increase may not be required for a temporaryplatform.

2. Pre-treatment requiredClays that can be rendered suitable for stabilisation by pre-treatment with lime. Typically 2-3% by weight of lime isrequired to reduce water content and plasticity and enable mechanical mixing. Silts and mixtures of granular soils with ahigh clay content will also need pretreatment.

3. Not treatableSome materials are difficult to stabilise because they are unsuitable chemically or may require excessive mechanical

modification. Highly acidic materials may require careful binder selection as they can delay setting of cement. Sulfate-rich soils can cause swelling and disintegration of cement-bound layers; this can be associated with water uptake andrapid softening of stabilised clays. Whilst this may only be an issue for platforms incorporated in permanent works 5, therisk posed by heave should be identified for both short and long term applications and testing may be consideredappropriate.

If stabilisation is a viable prospect, the material, if granular, should then be laboratory tested to determine its gradingand, if cohesive, its liquid and plastic limits and in situ moisture content, or all if necessary.

2.1.2. SI for temporary platform designThe design of a temporary platform requires information about each load bearing layer. The subgrade is in generalcharacterised by an undrained shear strength (cohesive, c u) or angle of shearing resistance (granular, '); representativevalues should be identified for the areas of platform to be designed.

2.1.3. SI for permanent works designThe later applications for the working platform may require further information for design purposes. Whilst in generalvolume stability of a temporary platform will not be an issue, the sulfate content of soils to be treated may well need tobe addressed if the risk of heave is considered sufficient for temporary or permanent works. Permanent works designmay require this consideration 6.

Reuse of the platform as a pavement area may require SI to be carried out for design to Highways Agency guidance 7.Other applications may also have specific guidance, covered by existing and emerging standards 8.

2.1.4. SI for HBM installationThe binder quantities may depend on the condition of the soils at the time of stabilisation. It will be important that the

site investigation information can be related directly to the HBM strength development timescale.It is important to assess the condition of the subgrade (beneath the HBM layer) as this may have an impact oninstallation as well as overall platform design. The subgrade must be sufficiently stiff that compaction of the HBM layercan be carried out. In situ tests can be used. Guidance on subgrade assessment is given in HD25 9.

4 Cement-bound materials for sub-bases and road bases. BCA 46.027 (1990)5 Special Digest 1. Concrete in aggressive ground. BRE. (2005)6 See HA74/00 and Britpave publication BP/16 - Stabilisation of Sulfate Bearing Soils7 Design Manual for Roads and Bridges DMRB Volume 4, HA 74/00 gives guidelines for both SI and testing8 BS EN 13285 Unbound and hydraulically bound mixtures (test methods), BS EN 14227:2004. Hydraulically boundmixtures Specifications, BS1924:1990. Stabilized materials for civil engineering purposes.9

HD 25/94 Highways Agency DMRB Vol 7 Sect 2, Pt 2 indicates the scope of SI needed for pavements, note that thismay be too onerous for many temporary applications. This has now been superseded by IAN 25/06.


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2.2. Pre-construction site assessment Check site investigation findings Current site drainage Latest information on working platform location and level

The site investigation information available before the construction stage of a project commences may be inadequatewith regard to the needs of working platform design and installation.

Table 3. SI requirement. Issue Requirement

SI information doesn't relate to current location(level and/or area) of platform as SI oftencarried out well before main works

Essential to test soils that will be stabilised, samples must berepresentative

A supplementary SI may be neededSI information doesn't give sufficient informationfor platform design as SI may not give sufficientinformation if it has not been targeted at theplatform design

Definition of materials properties for HBM or other parameters maybe needed

A supplementary SI may be needed

When the site becomes available for construction, existing information should be reviewed, any additional requirementsidentified and, if required, further specific site investigation carried out.

Site drainage requirements may vary throughout the year and the need for any additional drainage should be assessedand incorporated into the platform construction programme. Weather, particularly temperature, may be important forthe setting or the development of strength of some HBM binders.

Last minute project design changes can lead to changes in construction, and thereby working platform levels. Thepotential implications of such changes, particularly when there is cut and fill on a site, should be recognised and theworking platform designer informed.

2.3. Site preparation Excavation and backfilling of weaker zones and old foundations and services Deterioration of subgrade Inspection of subgrade prior to installation of platform

The specialist subcontractor responsible for the installation of the HBM layer generally carries out the site assessmentand may specify or carry out preparation.

During site preparation, weak or variable areas should be identified. Often this is carried out by proof-rolling the platformarea. It may be necessary to excavate localised weaker zones, old foundations and abandoned services. Suchexcavations should be backfilled to an appropriate level with material suitable for the stabilisation process. Generally forin situ stabilisation this would consist of fill of similar nature to the rest of the pre-treated material. A granular fill, wellcompacted, would be a suitable infill when overlaid by ex situ HBM.

Major changes in site level can have a significant effect and should be checked against the design.

When ex situ mixing is utilised, the preparation of the layer to receive the HBM is no different from that required for anyoversite material, and the usual care and consideration paid to its compaction, surface levels and profile. HBM materialshould never be laid on frozen or softened material, standing water or any other unsuitable materials 10.

10 Highways Agency MCDHW Vol. 1 Series 800 details requirements for subgrades to receive HBM


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Site preparation (Beach Stabilisation Division)

Prior to in situ stabilisation, the formation should be graded to achieve the required level of the final treated layer, withallowance made for bulking. This can be 2-5% for lime stabilisation or lime/cement stabilisation of clayey soils. The leveland density of the soil prior to treatment can determine the accuracy of the mixing depth, final thickness and overallstrength and consistency of the layer.

An allowance for bulking during mixing should be made (Geofirma)


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3. Design3.1. General features Overall approach related to risk and performance requirements Competence of designer Parties with input to the design Constraints on level of working platform Edge effects Sloping sites Access ramps

The approach to platform design should be related to the risks which have been identified in connection with the plantfor which a platform is required and with the operations to be carried out, as well as the soil conditions. A simple designapproach for working platforms may be appropriate for many routine temporary cases. Where the HBM layer also formspart of the permanent works, a design method appropriate to that end use should also be carried out.

The design of a working platform is a geotechnical design process and should be carried out by a competent person. Thedesigner should have full access to the health and safety plan, including the desk study and all other site investigationinformation. This guide is not intended to replace or reduce the designer's input, but rather to promote theimplementation of minimum design, installation and maintenance standards.

As a minimum the parties identified inTable 4 should have input into the design which will generally be critical for defining the requirements of the workingplatform.

Table 4. Parties who should have input into platform design. Party Inputs

Permanent works designer Additional uses for the platform as part of the overall developmentor to define materials that may be re-used

Principal contractor Other construction activities purposes for which they would usethe platform, timetable of activities

Contractor or subcontractor Requirements for platform performance, including gradients,ramps and edges

The platform level may be dictated by construction requirements rather than the final design of the permanent structure.This should be considered early in the design and construction process to ensure that where possible working platformscan be re-used for other purposes.

Attention needs to be given to the edges of working platforms. It should be determined how near the edge of theplatform plant and vehicles can be permitted while avoiding instability. A minimum distance of half a machine width isusually required for tracked plant and clear marking of the acceptable working area for the design is essential.

Sites where there have been cut and fill operations, or where plant is required to operate near slopes or batters, willneed to be checked for stability of earthworks or other structures with the additional loading of the plant in place.Sloping sites present particular problems for stability, which should be addressed in the design. In general a slope of 1 in10 provides a limit for plant stability.

Access ramps can be a problem. They should be sufficiently wide and stable to permit safe movement of rigs and cranesand should be graded to plant-specific and drainage requirements. The base of access ramps may require additionalstrengthening.

3.2. HBM mixture design Identify binders Find optimum moisture content for good compaction conditions Confirm binder content

Assess strength gain and rate of gain Platform usage


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This section provides a very simple guide to HBM mixture design. More comprehensive guidance can be found in BS EN14227 11 and publications produced by the BCA 4 and Britpave 12. Preparation and testing of samples should be carried outin a way and to a timescale that reflects field conditions and the plant to be used as well as the time period before theplatform will be used.

Experience has shown that HBMs, designed to be compacted by rolling, exhibit a relationship between moisture contentand compaction similar to that found by Proctor 13 for soils. A relationship exists between the moisture content of the mixand the dry density obtainable by means of a given amount of compaction by rolling. It has also been found that thestrength of a HBM is dependent upon binder type(s), binder content and dry density so that: There is an optimum moisture content (OMC) for compaction, above or below which dry densities are reduced. For a constant binder content and moisture content, strength increases as the dry density increases. For a constant dry density and moisture content, strength generally increases as the binder content increases 14.

Knowledge of binder options and these three relationships form the basis of mix design procedure for HBMs.

A simple step-by-step description of the design process is as follows:Step 1 Identify soils, categorise by type, plasticity, moisture content and gradingStep 2 Select appropriate binder, estimate quantityStep 3 Mix, compact and cure samples.Step 4 Test for strength (generally at 28 days)

Step 5 Iterate 2-4 until strength required is obtained at correct timescale15

.

HBM design can be divided into design for granular or aggregate-based HBM's and those stabilising cohesive soils.

3.2.1. Binders and soil modifiersThe most common binders or modifiers and their general uses are: Lime (usually quicklime) is a soil modifier used to reduce the moisture content and/or plasticity index of

unacceptable cohesive materials and to reduce the moisture content of granular materials. Cement is primarily used to increase strength, although moisture content will be reduced due to hydration of the

cement. Compaction must be undertaken within 2 hours of mixing due to the rapid setting of cement boundmixtures.

Lime and cement. Some cohesive materials do not achieve the required strength when lime alone is added socement is added to achieve the required strength. In this two stage process the initial addition of lime is primarily to

make the cohesive material friable so that the cement can be mixed successfully. Ground granulated blast furnace slag (GGBS) is a hydraulic binder that gains strength more slowly than cement. Activation by lime is common. GGBS can also be used with cement.

Pulverised fuel ash (PFA) is a pozzolanic material that reacts with lime to cause a strength increase. As with GGBSthis is a relatively slow reaction that is temperature dependent. PFA can also be used with cement.

A number of binders or combinations, can also be used 16.

3.2.2. Determination of binder quantity 17 For determination of the binder content, specimens for strength testing have to be prepared with a range of binderquantities. Using values of moisture content determined 18 samples should be prepared and tested 19 and a suitable bindercontent selected based on the strength, or other, design requirements. Both testing and binder choice should reflect thetimescale over which the strength gain is required - for example if a platform is to be used very soon after construction,cement will generally be required.

Testing for frost susceptibility may also be required if the platform is to be incorporated into the permanent works orwhere heave may pose a risk even in the temporary case.

11 A guide to the use and specification of cold recycled materials for the maintenance or road pavements TRL report 611,Merrill, Nunn & Carswell. 2004. ISBN 0968-4107. Replaces TRL report 38612 Stabilised soils as subbase or base for roads and other pavements. Technical Data Sheet BP/08, Britpave. (2004)13 Note that for non-cohesive soils or aggregates compaction by vibrating hammer is more appropriate.14 Whilst this is generally true, there is often an optimum binder content15 It can be difficult to accurately predict HBM strength, particularly where soils are variable and testing may be anessential step in mix design16 An example is ENV 13282:2000 Hydraulic road binders - composition, specifications and conformity criteria17 BRITPAVE design note BP/1318 determination of optimum moisture content see testing methods in BS EN 1328619 determination of binder composition, see Britpave BP/08


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Generally binder contents are chosen that result in strengths of around 2N/mm 2 (strength class C1.5/2.0) which hasbeen found reasonable for platforms for most construction activities.

Different construction processes carried out on or through the platform may impose strength requirements that need tobe taken into account in the HBM design. A platform that is very strong may form an ideal running surface for plant butthis may cause problems in the construction process if drainage runs cannot be dug.

Typical foundation construction processes that require a platform that can be penetrated may have limitations such as: CFA, bored piles and bored minipiles are unlikely to have difficulty in penetrating most HBM platforms Driven piles and bored displacement piles can penetrate some stabilised platforms but the platform may crack

unless preboring is employed (or trenching for sheet piles) especially if UCS strength is greater than 0.5N/mm 2. Vibroflots (for vibro compaction, vibro columns or vibro concrete column construction) have been found effective for

platforms thinner than 500mm, for greater thicknesses than this pre-boring would be required. Dynamic Compaction - a HBM platform is not a recommended solution for dynamic compaction, since repeatedly

dropping a heavy weight breaks up the stabilised layer, which can degrade further in wet weather.

Driven piling rigs operating on stabilised platforms (Rock and Alluvium, Aarsleff)

3.3. Geotechnical design (including drainage and combined platforms) Loading used in design calculations Weight of plant Distribution of pressure under machine tracks Crane outriggers Wheeled plant

3.3.1. Working platform design for tracked plant.Loading.It is not easy to reflect in the design calculations the loading which will actually be experienced by a working platform.Radically simplified stress distributions are generally used in design calculations.

The contractor or sub-contractor should provide the platform designer with a list of plant and equipment which will beused in the specialist work carried out from the platform, together with the maximum ground pressure and loaded areasfor each item.

Where loading is imposed by drilling rigs this should be calculated according to EN 791:1996 (Drill rigs - safety) and EN996:1996 (Piling equipment - safety requirements) to determine the maximum ground pressure that could be exerted bythe equipment. Methods of calculating the distribution of pressures under machine tracks are given in these twoEuropean Standards. For specific cranes or piling equipment, the maximum track pressures can be estimated by staticcalculation for critical jib positions by methods specified in these standards. This requires the consideration of the fullrange of orientation of the rig in relation to the tracks under a range of operating conditions and identification of theworst combinations. Special consideration should be given to the pressures from loads imposed by stabilising pads and


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skid mounted rigs. It should be noted that, in general, for working construction plant the pressure imposed cannot becalculated simply using the plant weight and footprint.

Loading imposed by piling rigs must be calculated according to EN791 (Cementation FoundationsSkanska)

Non-uniform loading distributions can be transformed into equivalent uniform loads over a reduced area extent using themethod described by Meyerhof 20.

Platform thicknessThus far, there has been no reported failure of an HBM platform. However, as yet, no universally accepted method forthe design of platforms constructed from HBM layers exists. A platform design should be able to identify the ultimatefailure load, or at least the minimum factor of safety inherent in the thickness and strength of platform chosen on agiven subgrade that experiences a given working load. It should be noted that strength is time-dependent for a HBM

layer and the worst case must be identified for checking in the design thickness. Experience in HBM design thus far hasbeen limited to the design of pavement layers, for which the number of load cycles is very high and 'failure' is aserviceability issue generally characterised by excessive deformation.

Currently platforms are designed using simplified methods and calibrated by the experience gained in their use fortemporary and permanent works elements.

A simple method for the design of granular working platforms, including subgrade and platform contributions to bearingcapacity, can be found in BR470 'Working platforms for tracked plant'. Reference can be made to CIRIA C752 (Cranesafety on site) for a discussion of outrigger support methods and CIRIA SP121 for an alternative method for granularworking platforms. BR470 assumes a 'punching' failure mode for the granular platform in conjunction with a bearingcapacity failure in the subgrade.

The punching mechanism may not accurately describe the failure associated with an HBM layer, given that they areconstructed using a wide range of materials on varied subgrades. Use of this method should be limited to thoseoccasions where: the failure mechanism is possible, the HBM can be characterised by a density and angle of shearing resistance ( ') and experience exists of similar situations.

A lower bound to the failure load could be attained using this method for granular HBM's, by assuming unboundconditions. Depending on the timescale for the project, both short term and long term conditions may need to bechecked.

The characterisation of HBM using an angle of shear resistance ( ') is not a simple process and should be carried outusing past experience of similar stabilised material and, if possible the results of testing on representative samples. Some

20 Meyerhof GG (1953) The bearing capacity of foundations under eccentric and inclined loads. Proc. 3 rd InternationalConference on Soil Mechanics and Foundation Engineering, Zurich, vol 1, pp440-445.


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shear box testing has been carried out, and designs using ' in excess of 40 degrees have been found adequate. It ismost likely that this representation is applicable only to relatively weak HBM-soil mixtures. Shear box testing must becritically analysed for any given HBM; specimen size versus the largest aggregate size may be an issue for somemixtures with large particles; testing may not adequately represent the likely failure plane (which may in practice fall ona discontinuity). As yet there is insufficient data to judge whether compressive strength is a good indicator for shearstrength.

Design calculations should indicate the minimum thickness of working platform that is required for the given HBM,subgrade and loading conditions. However, any design method is likely to contain many simplifying assumptions andthere may be considerable variability in near-surface ground conditions, hence achievable strength. It is important,therefore that the results of calculations are critically appraised by a competent person.

Platform thickness is one element of design (McArdle Stabilisation)

Where design falls outside the previous experience of the platform designer and installer, or where conditions dictatesuch as very early use of the platform or adverse weather conditions, the platform can be checked using in situ tests. Insitu plate testing can be used to verify the working load, provided that the plate is sufficiently large (suggested minimum600mm diameter).

3.3.2. Design for wheeled plantPlatforms may be subjected to single or repeated loading from wheeled plant. The worst case of repeated loading maybe imposed by concrete wagons. Simplified design of HBM pavements can be used to design the working platform forthese cases, using a relatively low number of passes to determine the design criteria. TRL 611 Tables 7.4 and 7.5 forexample show thickness design for bound layers 11 for light commercial use that can form a major part of a pavement

foundation. Alternatively TRRL LR1132 can be used to estimate sub-base thickness required to carry construction plant.

3.3.3. DrainageHBM materials are likely to have very low permeability. Hence drainage design is critical, to ensure that the platformremains suitable for use and not waterlogged.

In general this can be carried out by careful construction of the platform layer. Falls can be constructed into the platformby means of grading during final compaction. Large areas may require falls to intermediate drains as plant stabilitynecessitates a maximum gradient of 1 in 10.

In all cases the requirements of the construction timescale should be taken into account - winter working may requiredrainage design for heavier rainfalls and account taken of the raising of the water table beneath the platform. Similarlyice forming on the platform due to the presence of standing water can render construction activities dangerous. In the

worst cases it may be necessary to place a granular topping layer.


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Due consideration must be given to the piling process employed. Some piling techniques will cause groundwater to bedeposited on top of the platform and this quantity must be added to that from rainfall and any rising groundwater table.

Also if the piling technique employs a support fluid then this must also be taken into account.

Drainage design is essential for efficient use (Stent Foundations)

3.3.4. Design life

Use as a working platform Subsequent uses (see also section 6)

The intended duration of the working platform is a significant element in its design. The bearing resistance of theplatform may be reduced by degradation under repeated loading.

Where the working platform subsequently has other temporary or permanent uses, the extent of degradation during itsuse as a working platform may become critical. Piling or other works on the platform may leave it contaminated.However, the incorporation of the platform into the permanent works can save significantly on cost and programme.Furthermore, there is a tendency on site to take greater care of the platform if it is seen as part of the permanentstructure.

Examples of subsequent uses of the platform may be: Re-use as temporary works for later construction activities, such as use of the platform for formwork Re-use as pavement layer, where permanent works design must be carried out.

Reuse may, for weakly bound HBM, require removal of say 30mm of material and/or regrading. For some uses, in situtesting of the platform may also be necessary. Reconstitution of drainage may be necessary after piling works.


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4. Platform Construction Specification Methodology Quality control Site hazards Environmental factors Edge of working platform Performance testing

Specifications for HBM construction can be found in TRL 611. Although this relates to highway maintenance works, itdoes highlight the key issues that may need to be considered for platforms. Where a temporary application is required,the specification may not require as much process control.

HBM construction requires slightly different process controls depending on the construction method and the binder typeto be used.

Table 5. HBM construction methods. Item In situ Ex situ

Binder storage andmixing

Storage of binders for in place mixing Storage of binders for batching prior to laying

Mix constituents Check in situ soils are as anticipated, onlymix in appropriate weather conditions

Check material being batched is of appropriateand consistent grading

Mixing Binder may be:Spread on soil and rotavated. 21 Mixed in situ using enclosed machinery

Mixing in batching plant

Compaction HBM must be compacted as a single layerCompaction must take place quickly aftermixing if cement is used as a binder, thisis less critical for slower-setting bindersPoor compaction leads to low strengthGenerally a larger area is mixed thanrequired to ensure restraint and goodcompaction in the platform area

HBM can be compacted in multiple layers asrequired. Compaction must take place quicklyafter mixing if cement is used as a binder, this isless critical for slower-setting bindersPoor compaction leads to low strengthEdge restraint during compaction ensurescompaction is effective up to the boundary

Control testing In situ testing; tests on samples manufactured from mixed materialsGrading The surface may be graded to form a final levelSealing The surface is often sealed with a bitumen emulsion to maintain its moisture content during

curing

21 If soil is very high plasticity a two-pass mixing process may be needed.


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Grading and compaction of HBM layer (Beach Soil Stabilisation)

Spraying of bitumen surfacing (Sitebatch Technologies Ltd)

Quality controls may also be required, particularly where the platform forms part of the permanent works. This mayrequire testing of the consistency of the mix, a check on the in situ soil CBR, records of binder quantity and mix depth,testing of density of the final HBM layer or samples compacted at the same time.

A final check on platform strength may be required prior to plant using it (see section 3.3.1). in addition, performancetesting may be specified. The extent of the testing and its composition will depend on the treatment as well as theperformance requirements of the platform in the short and long term. Early life performance may not be completelywithin the control of the contractor (as temperature impacts the strength development) and this should be taken intoaccount. TRL 611 and HA74/00 describe a number of tests for compliance and performance measurement.


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Performance testing, here using plate test of smaller diameter than minimum recommended for workingplatform (Geofirma)

Construction of drainage may be necessary to prevent water or piling slurry from lying on the platform or spilling ontoadjacent areas or contaminating water courses.

The boundaries of the permissible working area should be clearly marked.

4.1.2. Environmental and safety issues in HBM construction

Site hazardsWhere underground and overhead services are present, markers should be provided and maintained in accordance with

the requirements of the relevant statutory authorities. The working platform level may be dictated by the levels of theseexisting services.

MaterialsSafe and dry storage, handling and use of binders requires careful site preparation, an awareness of the local constraintsand good selection of appropriate mixing techniques.

Short and long term risks should be considered:

The materials used in the stabilisation operation may need to form part of the Environmental Management Systemfor the site works. In general the same issues as for concrete and cement must be addressed, specific riskassessments and COSHH assessments will need to be carried out.

Mixing methods that require spreading of dry binder prior to mixing may not be appropriate for sites in close

proximity to possible receptors (this could be human, natural or other building environments), particularly in windyweather. Techniques that carry out mixing in an enclosed environment release little dust and are better suited tosuch situations.

Interceptor ditches may be necessary to prevent water or slurry from spilling onto adjacent areas or contaminatingwater courses.

Longer term risks may arise from possible leaching from the bound material, and should include the potential forchanges in pH accompanying stabilisation to change mobility of some elements. In some cases, stabilisation hasbeen used as an effective means of providing a capping layer over mildly contaminated ground 22.

22 BCA A guide to the treatment of contaminated land by stabilisation/solidification


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5. Operation, Maintenance and Repair Control of working platform Usage of platform Prevention of deleterious works Importance of maintenance Monitoring and remediation Repair Safety regulations

Throughout its working life, the platform should be under the day-to-day control of competent site staff. Contractualarrangements should ensure that the platform is adequately inspected, controlled and maintained.

Regular observation of platform performance is essential to ensure that the design assumptions are reasonable andremain valid throughout the platform life.

The working platform has been designed and installed to be safely used by certain plant. Site control should be

adequate to ensure that it is not used by plant for which it has not been designed and that only designated workingareas are used. Problems may arise where working platforms are also used as haul roads. A number of factors related tothe usage of the working platform will affect its performance and hence the required maintenance:

type of rigs and service cranes used and dynamic or vibratory effects due to their operation frequency of passage across the platform of service cranes with heavy loads frequency of passage of concrete trucks/supply vehicles which may be restricted to routes where the platform has

been strengthened scale and duration of works drainage, contamination, degradation of material acceptable minimum thickness stated in design.

Inadequate performance of working platforms may be due to poor maintenance and many of the problems experiencedwith rig instability can be associated with failure to adequately maintain and, where necessary, repair a working platformrather than with inadequacies in specification or installation.

The working platform should be reasonably level, well drained and kept in good condition for the duration of the works.Timely and appropriate maintenance relies mostly upon adequate monitoring and remediation on site by the contractorresponsible for the platform. Careful surveillance can detect a deteriorating situation before it becomes a major hazard.Simple checks on platform thickness can be made using profile boards. Deformation or cracking of the platform surfaceshould be routinely observed and maintenance carried out when necessary.

Maintenance of heavily trafficked areas such as access routes and ramps requires special attention. Problems can becaused by plant spragging, heavy concrete wagons and other traffic. Contamination may be caused by mud from thesite, from machine wheels or tracks, from specialist operations involving spoil generation or specialist materials such asbentonite. Poor drainage can cause difficulties and flow of water across the surface of the platform should be avoided.Generally routine maintenance will involve cleaning off the platform surface. Maintenance of drainage may require:

water to be pumped off the working area drainage channels to be maintained soakaways installed stone surface dressing placed if water is causing a problem that cannot otherwise be resolved.

Any site activity that could affect the integrity of the working platform, such as an excavation through the platform,should only be permitted if it is supervised by competent site staff and adequately reinstated to the original specification.

All excavations should be backfilled with material of similar characteristics to the platform and must achieve the strengthrequired at the time the platform is to be used. Repairs should also be carried out such that the HBM material of theplatform is not damaged by water ingress. In practice this will often involve backfilling excavations with lean mix orfoamed concrete. Damage to the platform should be repaired promptly so that the platform is reinstated to the requiredspecification.


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Specialist stabilisation plant reduces dust generation during the mixing process (O' Keefe SoilRemediation)

Irrespective of who designs the platform, the principal contractor under the CDM regulations is responsible for safety onsite and should be in overall control of all other contractors working on the site. The principal contractor is therefore thebody with sufficient control to be responsible for ensuring that the platform is adequately maintained and repaired.


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6. Use for and interface with permanentworks (formwork, blinding, foundationfor pavements etc)

The following list is not intended to be exhaustive, rather to demonstrate that a working platform constructed of durablematerials such as HBM can perform a number of tasks in the construction programme. Key issues related to theexamples are listed. The case studies in the project report show examples of where HBM platforms have beensuccessfully reused and the references list in Section 7 gives sources for further guidance.

6.1. Construction activitiesConstruction platform

A durable and level surface improves the efficiency and safety of all construction activities. Particular examples requiring

significant support may be steelwork erection, mobile cranes, concrete trucks and formwork.

Checks will be needed that the strength and platform thickness are sufficient for the activities to take place on theplatform; this should be critically assessed after any previous activities have taken place.

FormworkHBM can be sawn through to provide accurate in situ formwork for foundation pads. Strength of the HBM is generallynot an issue, but the formwork requirements may determine the platform thickness.

BlindingThe level of a blinding layer for a ground bearing slab needs to be graded and cleaned off prior to concreting.

6.2. Permanent worksGround bearing slabThe HBM layer can be used to improve the foundation for a ground bearing slab. This can be used in designing the slabto provide advantage in terms of slab thickness.

Car parksHBM layers are often used as car parking with very limited pavement layers laid on top of the HBM surface. An in situCBR can be used to characterise the weaker HBM once the surface has been cleaned off.

Non-adopted/ minor roadsThe HBM layer can form the major foundation and pavement components. A value of in situ strength (characterised byCBR) can be used to design the pavement layers 23.

Adopted roadsThe use of an HBM foundation can significantly reduce the required thickness of pavement layers. HD 25/94 (nowreplaced by IAN73/06) describes the current design methodology adopted by the Highways Agency. This is also likely tobe sufficient for roads to be adopted by Local Authorities.

Stabilisation of contaminationStabilisation/solidification (s/s), by mixing soil with binder, can be used to immobilise contaminants. The mix design musttake into account the different requirements of contaminant immobilisation. Two key references for the design,construction and monitoring of s/s remediation of contaminated land are given in the bibliography.

23 BRITPAVE BP/08


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7. Standards and references7.1. Standards

BS EN 14227:2004. Hydraulically bound mixtures Specifications

Part 1: Cement bound granular mixtures (CBGM). Part 2: Slag bound mixtures (SBM). Part 3: Fly ash bound mixtures (FABM). Part 4: Fly ash (FA*) for hydraulically bound mixtures. Part 5: Hydraulic road binder bound mixtures (HRBBM).

European standard for the constituents, mixture typesand performance requirements for granular materialstreated with cement and other hydraulic binders andcombinations for use in earthworks and pavements

prEN 14227 Hydraulically bound mixtures Specifications

Part 10: Soil treated by cement (SC). Part 11: Soil treated by lime (SL). Part 12: Soil treated by slag (SS). Part 13: Soil treated by hydraulic road binder (SHRB). Part 14: Soil treated by fly ash (SFA).

European standard for the constituents, mixture typesand performance requirements for soil treated withcement and other hydraulic binders and combinations foruse in earthworks and pavements. Standards are in thefinal stages before UK implementation

BS EN 13286:2003, 2004, 2005 . Unbound andhydraulically bound mixtures Part 1 to 5, 7, & 40-53.

Test methods for HBM covering; laboratory compaction,specimen manufacture, laboratory mechanicalperformance testing and miscellaneous tests covering,swelling, pulverization, workability period, slag alphacoefficient, MCV, & immediate bearing index (IBI)

BS1924:1990 . Stabilised materials for civil engineeringpurposes.

Test methods for soils treated by cement and lime

7.2. Bibliography

Highways Agency HD25/94 Pavement design and maintenance - Foundations (now replaced by Interim Advice Note IAN73/06)HD74/00 Treatment of fill and capping materials using either lime or cement or both(under revision 2006)Specification for Highways Works Series' 800 and 1100

TRL TRL 611 A guide to the use and specification of cold recycled materials for themaintenance of road pavements(updates TRL 386 Design guide and specification for structural maintenance ofhighway pavements by cold in situ recycling)TRRL 1132 The structural design of bituminous roads

Britpave BP/08 Stabilised soils as a sub-base for roads and other pavementsBP/13 Cement and other hydraulically bound mixtures: the new European standard.BS EN 14227, Parts 1-5.BP/14 Immediate trafficking of cement bound materialsBP/15 Soil stabilisation - guidelines for best practiceBP/16 Stabilisation of sulfate-bearing soilswww.soilstabilisation.org.uk


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WRAP Promoting the use of applications incorporating recycled and secondary aggregatesin HBM : Research ReportHBM technical guidance - No.1 Major RoadsHBM technical guidance - No. 2 Minor roads and paved areasHBM technical guidance - No. 5 Heavy duty pavingHBM Durability and Test methodsHBM Case Studieswww.wrap.org.uk

BCA / The Concrete Centre Essential Guide to Stabilisation / Solidification for the Remediation of Brownfield Landusing Cement and Lime. (The guide, reviews the process of s/s using a number ofbinders)Cement-bound materials for pavements: materials selection, mix design, constructionand testingwww.cementindustry.co.uk

Environment Agency Guidance for the use of Stabilisation/Solidification for the treatment of contaminatedsoil

Science report SC980003/SR1 can be downloaded fromwww.environment-agency.gov..uk

UK QUALITY ASH ASSOCIATION,

Technical data sheet 6.2: Laboratory mixture design for lime activated fly ash boundmixtures (FABM) for sub-base and road baseTechnical data sheet 6.5: LFA (lime treated fly ash) for capping and sub-baseTechnical data sheet 6.9: The role of PFA for enhanced stabilized cappingwww.ukqaa.org

7.2.1. Other references

[1] HEATH D C. The application of lime and cement soil stabilization at BAA airports. Paper 9817, Proceedings Institutionof Civil Engineers, 1992.[2] KOLIAS S & WILLIAMS R I T. Cement bound road materials: strength and elastic properties measured in thelaboratory. TRRL Supplementary Report 344, TRL, 1978.[3] SHERWOOD P T. The properties of cement stabilized materials. LR 205. Road Research Laboratory, Crowthorne,Berkshire, England, 1968.[4] SHERWOOD P T. Stabilized capping layers using either lime, or cement, or lime and cement. Contractor report 151.TRL, Berkshire, 1992.[5] THE EAST MIDLANDS GEOTECHNICAL GROUP OF THE INSTITUTION OF CIVIL ENGINEERS. Lime stabilization.Proceedings of the seminar held at Loughborough University Civil & Building Engineering Department, 25th September1996.[6] WILLIAMS R I T. Cement-treated pavements materials, design and construction. Elsevier Applied SciencePublishers, London, 1986.


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Appendix A Case studies

BMW Car Showroom at Costessey, Norwich

LIME MODIFIED AND CEMENT STABILISED WET FILL AS A WORKINGPLATFORM

Background

Project Information

Name LIND BMW Car ShowroomRegion East of EnglandType of project Commercial

Date March May 2005Client Lind Automotive GroupBuilding Design & Clients Agent Les Brown Associates

Planning & Development ConsultantsDesign Development Feilden & MawsonEngineer T A Millard Consulting EngineersMain Contractor Adonis Construction LimitedStabilisation Contractor OKeefe Soil Remediation (OKSR) Limited

The Project Adonis Construction Limited on behalf of the Lind Automotive Group, were contracted to construct a car

showroom facility at a site located at Costessey in Norfolk. The plot, which was approximately 30,000 m2,was to have three steel-framed car showrooms and associated parking, servicing and delivery areas (Figure1).

The site was part of the former Longwater sand and gravel extraction pit. Construction commenced in lateFebruary 2005 and was scheduled for completion in January 2006.

Figure 1: Completed individual steel framed car showrooms, associated parking,servicing and delivery areas

Ground ConditionsThe site surface consisted of gravely sand which was very soft, slightly clayey and also had areas of standingwater. It was believed that this material had recently been placed from an adjacent construction project andspread on the site.


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The fill material had an extremely high moisture content (in the initial 500 mm depth) and was in a slurry-like condition in certain areas. Access to large parts of the site with tracked plant was virtually impossibledue to the soft nature of the fill (Figure 2). California Bearing Ratio (CBR) values were less than 1%. Belowthis top 500 mm layer the fill materials were drier, more compact and were described as slightly clayeygravely sand.

Figure 2: Tracked plant and areas of standing water

Throughout early 2005, OKSR carried out extensive laboratory testing on recovered samples of the fillmaterial, including assessment of particle gradings, Atterberg limits, compaction studies and design mixtesting. Typically, moisture condition value (MCV) figures for the untreated natural fill material were below 4.For a normal material to be compacted as a fill, an MCV in the range 8 12 would be expected. Oncetreated with between 2 4% quicklime powder OKSR established that MCVs increased to levels where thefill had been adequately dried to allow for placement and compaction.

Regulatory/environmental issuesThere were no additional requirements beyond those normally required in a site of this nature e.g. the needto minimise dust in a site next to the A47, a busy highway.

Construction Specification and Related Details

SpecificationThe three car showrooms were intended to be placed on vibro-stone columns; however, the very soft natureof the fill material in its untreated state made it unsuitable for use as a working platform for the piling rigs.

Adonis Construction did not want to remove the 15,000 m3 of wet fill material and import a replacementstone material for reasons of both cost and time and therefore turned to considering a stabilized solution.

Following initial laboratory trials, OKSR suggested that the wet fill could be adequately dried and improved

by the addition of quicklime and its performance further enhanced by the addition of cement to create a working platform (Figure 3) across the entire construction site.


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Figure 3: HBM working platform

Design informationThe OKSR proposal was to construct a 500 mm working platform in two 250 mm layers with a targetstrength of 90% CBR using the addition of both lime and cement. The platform was to be used by the vibropiling contractor and subsequent trades e.g. Ground worker, steel frame erector and cladding contractorduring the main programme works. The stabilised platform upon completion of the piling would also doubleas a sub-base replacement layer to the car showrooms.

OKSR, following guidelines within the BRE publication on Working Platforms for Tracked Plant calculated asingle layer 250 mm thick of CBR 90% platform was sufficient for the vibro piling contractor to safelyoperate his rig. This platform was then increased to the full 500 mm depth for the loadings applied bysubsequent trades. The strength of the completed 500 mm platform to the car showrooms was such that allthe pile caps and strip footings were "sawn" out from the stabilised material; therefore, requiring noformwork to the foundations, no working space allowance and no backfill was necessary.

This resulted in increased efficiencies both in time and money to the whole project. As the construction of

the car show rooms progressed, the full 500 mm thick stabilised working platform was extended to thewhole of the external site area. The depth and strength of the lime and cement material replaced capping,sub-base and even lower asphalt layers, leaving just a requirement of 100 mm of surface and binder courseasphalt for all car parking, vehicle display areas and unloading areas.

Binder AdditionsQuicklime was initially added to the wet fill materials to reduce moisture content. Quicklime additions ofbetween 2 4% by weight were sufficient to bring MCV values from 4 or less to values between 8 10 andthus values suitable for subsequent use and treatment with cement. The enhanced working platformachieved the required CBR values of 90% and above with the addition of 5% CEM I Portland Cement afterthe lime addition.

Figure 4: Pile caps and strip footings sawn out from the stabilized material


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Construction processInitially a 250 mm working platform was created using both lime and cement to the building footprints as aplatform for Keller Ground Engineering who were installing vibro stone columns. Due to the very soft natureof the site, lime drying of the existing soil was commenced at the site entrance and slowly worked its wayacross the site until the whole area had been lime dried to give a workable material with minimum a MCV of8. Cement was then mixed to the building footprint areas to create the required 250 mm thick pilingplatform.

Both lime and cement were mixed into the site soils using OKSR's "integrated" soil recycling machine. Thismachine controls the emissions of dust, which was a key consideration working directly alongside theadjacent A47 dual carriageway. Each vibro-stone column position was set-out and pre-augured through the250 mm stabilised material, to allow the stone pile to be constructed.

Upon completion of the piling a further 250 mm of lime and cement stabilisation was placed onto thebuilding footprints, to create the full 500 mm depth, CBR 90% platform. This was partly a requirement fromthe structural engineer regarding the building loads and also to accommodate subsequent temporary plantloadings throughout the remainder of the contract period. The 500mm working platform was also created in

all external work areas of the project to act as foundation layers to car parks, roadways and vehicle displayareas. The stabilisation was graded to 10 mm throughout the car parking areas, thus allowing the 100 mmof surface and binder course asphalt to be laid without the need for additional regulating layers.

Figure 5: Wet fill material with the A47 dual carriageway in the background

Environmental EffectivenessThe in-situ treatment of very soft clayey gravely sand to create piling platforms for the car showroom projectat Costessey, saved the removal from site of approximately 15,000m3 of unsuitable material. This savednearly 2000 separate lorry movements and approximately the same number of movements to bring in anaggregate fill material. Producing HBM on site greatly decreased the impact of the construction project on

the local environment and also provided a good example of sustainable development, with large cost savingsand programme advantages for the construction team and the client.

The integrated soil recycling machine used on the car showroom project at Costessey differs from thecommonly used stabilisation machines in that it carries the stabilizer within an on-board hopper. Thestabilizer is discharged through the body of the machine into the underlying soil being processed. This hadthe advantage of reducing dust emissions during processing, which can occur with traditional spread androtovate stabilisation techniques (Figure 6). This was a key consideration when working in close proximityto the A47 dual carriageway.


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Rubber apron preventsairborne spread

Wet soil Variable mixing chamberwith milling and mixingmotor

Crumbly soil mixturewith reduced watercontent

Workingdirection

Rubber apron preventsairborne spread

Wet soil Variable mixing chamberwith milling and mixingmotor

Crumbly soil mixturewith reduced watercontent

Workingdirection

Figure 6: Photograph and cross-section of the main stabilisation machine

illustrating its reduced dust emission design

Performance results

StrengthIn-situ CBR testing carried out on each 250 mm layer of the stabilized working platform indicated an averageCBR value in excess of 100% 7 days curing after cement addition.

DensityIn-situ density checks confirmed that the working platform had been placed and compacted to achieve 95%of the materials maximum dry density (MDD).

Frost HeaveFrost heave tests (performed to BS1924:1990) were performed on the stabilised material. Test resultsindicated that the stabilised material was "non-frost susceptible". Recorded movement of test samples withinthe frost cabinet were only 0.8 mm. This was far below the allowable upper limit of 15 mm heave for a non-frost susceptible material.

Lessons LearntFor the client this site was an object lesson in how a relatively new technique can be so much better thantraditional methods. Amazement was expressed at the transformation of the site from its original wet andsaturated condition, and at the savings realised: at least 200,000 in lorry movements alone. The multi-tasking of the hydraulically bound material was impressive:

Unsuitable fill material at this site was dried and strengthened with the controlled addition of both

lime and cement to create a usable construction material. The stabilized material was used to support piling rigs during piling operations and was subsequently

used as a working platform for following trades. The stabilization was also engineered to replace the asphalt base layer to asphalt surfacing for all

car parking areas, which gave rise to financial benefits. The working platform was sawn through by the ground work subcontractor and was used as

permanent formwork for the foundation bases/pile caps Sub-base to the buildings.


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Lind Automotive Grou L ES B ROWN A SSOCIATESPlanning and Development Consultants


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University of East London Docklands Campus - Business School and KnowledgeDock Centre buildings at the Royal Albert Dock

LIME MODIFIED AND CEMENT STABILISED MADE GROUND AND ALLUVIALORGANIC CLAY DEPOSITS FOR 10,000 SQ M PILING PLATFORM

Background

Project Information

Name University of East London Docklands Campus - Business School andKnowledge Dock Centre buildings at the Royal Albert Dock

Region East London (South East region)Type of project Piling Platform ConstructionDate November December 2004Client University of East London (UEL)Structural Engineer Building Design PartnershipProject Manager Gardiner & Theobold Management ServicesMain Contractor HBG Construction (HBG)Stabilisation Contractor OKeefe Soil Remediation (OKSR) Limited

The ProjectThe new Business School and Knowledge Dock Centre (Figure 1) are a development continuation of the UELDocklands Campus. The buildings run along the Royal Albert Dock, a 2 km stretch of water adjacent to theRiver Thames.

The 61 week project to construct two new University buildings joined by a link bridge at their respective 2ndfloor levels, at a contract value of 21.5 M, is due for completion on 18 April 2006.

OKeefe Construction (Greenwich) Limited were awarded a subcontract to provide a piling platform as part ofthe overall enabling works plus the groundworks.

The Business School Centre building is a 9,000m2 steel frame structure with profiled metal cladding andcurtain walling. The 5 storey block, which houses the business school and a 400 seat lecture theatre, isfounded on 220 No. 500mm diameter, 20m deep continuous flight auger (CFA) piles. These were installedby HBW-BAM Grondtechniek working on the piling platform constructed by OKSR.

The Knowledge Dock Centre building is a 7,000m2 steel framed three-storey building with metal claddingand curtain walling. Similarly positioned on 180 No. CFA piles, the building houses laboratories and teaching

facilities.


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Figure 1: The new Business School and Knowledge Dock Centre buildingsnearing completion

Ground Conditions An exercise of trial pitting and sampling was carried out by OKSR laboratory to establish the range ofmaterial types and their moisture condition. Removal of existing oversite concrete revealed an assortment ofmade ground conditions overlying variable alluvial organic clay deposits to a depth of around 6 m. Organiccontent tests revealed organic values of up to 3.2% within the variable ground conditions.

Regulatory/environmental issuesThere were no additional requirements beyond those normally required in a site of this nature e.g. the needto minimise dust in a site next to Royal Albert Dock. Dust suppression was achieved using mixing plantswhich operate as an enclosed unit, carrying the binders on board and releasing/mixing them under the bodyof the machine. There is no need to spread and lay large volumes of binder on the surface of the groundprior to mixing, which can give rise to dust issues if windy.

Construction Specification and Related Details

SpecificationFollowing analysis of the variable made ground material recovered from the site trial pits, laboratory checksfor water soluble sulphate, acid soluble sulphate and total sulphur were carried out along with a series ofperformance checks. These included compaction studies followed by laboratory compacted CBR tests at arange of moisture contents using the proposed binder additions. From the results of these tests, a mixdesign including the addition of lime for the wetter areas of made ground, followed by Portland Cement waschosen to provide a 500mm thick piling platform with a California Bearing Ratio (CBR) of >50%. Thethickness and in situ strength of the platform were determined after a comprehensive set of conepenetrometer tests (carried out by Lankelma CPT Ltd) to meet HBGs proposal to use a 73 tonne piling rig

with a 39 m high stick.

Design informationThe piling platform design was carried out by OSKR based upon information supplied by principle contractorHBG and following the design guidelines detailed within the BRE publication Working Platforms for TrackedPlant.

Binder AdditionsThe binders used were lime and cement. The amount of lime addition was tailored to suit the groundconditions on site, in order to bring the soil to an appropriate state ready to receive the cement treatment.The quantity of lime added depended upon the soils moisture content, however, typically 2-3% was added.Following lime conditioning, Portland Cement was mixed into the made ground. Prior laboratory testing

confirmed that 5% (95kg/m3) of Portland cement would be sufficient to achieve the desired design strengthof the platform e.g.. >50% CBR.


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Construction processOnce the oversite concrete had been lifted and crushed and the 12,000 m area site reduced to level,stabilisation was carried out over a two week program during November and December 2004 using anintegral spreading and mixing machine. On completion of the works, plate loading tests were carried out byScientifics testing laboratory to verify the in-situ performance of the mat.

A total of 400 piles of 500 mm diameter and up to 20 m in length, were installed over the following 2months (Figure 2).

Figure 2: CFA piling rig carrying out operations on the500 mm deep in-situ stabilised piling platform

Following completion of the piling operation, the stabilised mat provided a durable weatherproof platformover the following year for the remaining construction of a series of laboratory andclassroom/teaching/research facilities for the University.

Environmental EffectivenessThe successful in-situ treatment of the existing made ground at this project with lime and Portland cementbinders to create a working platform gave a number of environmental benefits.

The soft clay/sandy made-ground, complete with brick, concrete and tile fragments, was unsuitable as aconstruction fill material without treatment. In a traditional construction project, this made ground wouldhave been excavated, loaded onto lorries and taken to a landfill site. This specific project alone would havegenerated in excess of 5,000 m3 of spoil for landfill using approximately 600 lorry movements at a cost of96,000. Subsequent to that removal, 5,000 m3 of aggregate would have needed to be imported and placedon the site. The ability to re-use the sites existing made ground resulted in a dramatic reduction of lorrymovements and less impact on the local community and road network.

Performance results

Independent plate bearing tests were performed in situ on the stabilized working platform by ScientificsLimited. Plate tests were performed across the platform using 600 mm diameter plates, which were loadedwith a maximum of 16 tonnes. The test results gave equivalent CBR values throughout the stabilizedworking platform of over 200% CBR (Figure 3).


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Project Fonda (Debenhams Regional Distribution Centre), Peterborough

CEMENT STABILISED PFA AS FILL, WORKING PLATFORM AND EXTERNAL AREAS FOR A DISTRIBUTION CENTRE

Background

Project Information

Name Project Fonda (Debenham's Regional Distribution Centre), PeterboroughRegion East of EnglandType of project Piling platform construction

External areas sub-base constructionDate October 2003 June 2004Client Prologis DevelopmentsEngineer Nolan AssociatesMain Contractor Winvic Construction LimitedStabilisation Contractor Geofirma Soils Engineering Ltd

The ProjectThe project involved the construction of a single storey warehouse with offices, associated service yards andcar parks totalling 120,000 m2 on an old PFA lagoon (Figure 1). Due to the poor nature of the ground, thebuilding was fully suspended on piles driven into the underlying Oxford Clay.

An earthmoving exercise was undertaken amounting to 36,000 m3 of cut and fill to utilise the upper metreof PFA to form the building platform. This PFA fill was cement-stabilised to provide a stable platform due tothe soft nature of the PFA. Once the site was excavated and filled to reach design levels, the upper 300 mm

of PFA was further cement stabilised to provide a sub-base for the externals hard-standings and a piling matfor the building area.

A nominal thickness of Type 1 stone (amounting to 50 mm over the externals and 7 mm to the building) wasincorporated into the stabilised PFA sub-base to provide added strength and durability to the stabilised layer.

Figure 1: PFA lagoon

Ground ConditionsBorehole and trial pit records showed the site to be underlain by a thick cover of made ground (PFA or clay

fill) within former brick clay pits, upon initially weathered solid geology of Oxford Clay. Trial pits within thePFA fill encountered water seepages, generally at approximately 1.00m depth below the base of the crust


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of the PFA fill, at 1.30 m to 2.50 m depth. Levels were expected to rise to within 1.00 m of the surfaceduring wet periods.

Total sulfates were reported as exceeding 1% in the Oxford Clay, up to 5% in places. Because of thepresence of sulfate minerals and total sulfate values above 1%, the Oxford Clay was deemed to beunsuitable for lime/cement treatment and was omitted from the works. Sulfate levels in the PFA werehowever, deemed to be suitable (as proven by prior laboratory testing and comprehensive compliancetesting in the field).

It was assumed that the sub-grade would provide a CBR of 2% as long as at least 1m of the PFA crustremained. The PFA was tested prior to commencement of the work and was found to be suitable fortreatment. This was subsequently proven by extensive on-going testing.

Regulatory/environmental issuesBecause of the metal contamination within the PFA and groundwater, the enclosed lagoon could not bedrained to allow the water table to be lowered or indeed to stop it rising due to rainfall. This limited theupp

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