Lime Stabilisation of Cohesive Soils for Capping …

1 HistoryLime treatment of Soils was introduced into a Department of TransportGuidance Note in 1976 and the full Capping specification into theSpecification for Highway Works ten years has been used onmany road projects since this date and is particularly beneficial in weakground or wet enables full use to be made of all sitematerials and minimises tipping and the import of SHW amended in May 2001 incorporated specifications for theproduction of Capping by using lime,lime and cement or cement only,which means that virtually any soil can be mechanics of Capping treatmentThe addition of quicklime (Calcium Oxide) to any soil causes areduction in moisture content as water is used in the hydration of will be enough to produce an improvement in theengineering properties of the Cohesive Soils there is a simultaneous improvement in thecondition of the clay particles due to a chemical change brought aboutby the calcium chemical change is known as Modification andis additional to the drying reaction essentially transformsthe material into a different soil with enhanced geotechnical characteristics,moisture condition value (MCV)

2 ,plastic limitand bearing capacity are all changed beneficially in this and Modification reactions occur immediately the quicklime isdispersed into the clays will lose plasticity and become morefriable due to the change in soil is these reactions that areessential to the production of Capping material and allows thepulverisation requirements of class 9E material to treated soil may need mixing more thanonce to achieve this part of the third reaction,which is unique to the design oflime stabilised Capping ,is the requirement forincreasing long term is achieved byraising the pH of the soil to by the addition of quicklime,which causes the silica and alumina in the clay to dissolve andform silicate aluminate hydrates form and bindthe soil particles is a temperature dependentreaction,which usually limits construction to the warmertimes of year when the shade temperature is 7 C or when the specified bearing ratio can be attained at atemperature lower than then 7 C may lime stabilisationcontinue to be carried must be taken to ensure thatdamage does not occur due to the effects of Stabilisation of CohesiveSoils for Capping layers usingQuicklimeIntroductionCohesive Soils can be treated with quicklime to produce cappingmaterial that complies with the Highways Agency specification results in.

3 A reduction in moisture content that occurs as the quicklime in soil properties due to physico-chemical cause an immediate reduction in the plasticity of clays and renders the soil more friable and workable with increased bearing long term improvement in strength due to the Stabilisation is a high strength and stiffness material used on weak fills andpoor acts as a working platform during the constructionof the pavement and as a structural layer in the long can becreated by treating low cost imported material,if the pavement levelsare low,and from insitu Soils if the levels are minimum strength requirement for Capping is a laboratory soakedCalifornia Bearing Ratio (CBR) of 15% after 7 days roadpavements the thickness of Capping is detailed in HD25 [2] and isdirectly related to the subgrade specification allows forseparate Capping and subbase layers or for one thinner layer composedentirely of subbase can also be produced by soilstabilisation and is covered in BLA Technical Data Sheet Highways Agency Specification for Highway Works (SHW)

4 Coverslime Stabilisation for Capping in Series requirements ofmaterial suitable for stabilising are covered in class 7E and theproperties of the stabilised material in class may also beproduced by the addition of cement,or lime and arealso available in SHW for these SuitabilityThe properties of the soil will determine the final properties of the lime stabilised quicklime combines with the clay minerals in the clay it is essentialto ensure that sufficient of these are present to develop the required Capping ,the greater the plasticity of the clay,the more clay minerals arepresent and a minimum Plasticity Index of 10 is specified by the insufficient clay is present to develop the required strength then cement may be addedas described in BLA Technical Data Sheet sulfate Soils can be treated but tests must be carried out to determine the levels present in the soil and ground sulfates are present where lime orcement are mixed with clay Soils ,it is possible for Ettringite crystals to form that swell and disrupt the stabilised tests should be carried out inaccordance with the procedures laid down in the Design Manual for Roads and Bridges (DMRB) Vol 7 [5]If sulfates are present consideration should be given to incorporating ground granulated blastfurnace slag (ggbs)

5 Into the mix in conjunction with lime,which canhave a beneficial effect on the heaving potential of the materials may have a detrimental effect on the Stabilisation process and may require higher additions of lime to be upper acceptabilitylimit of 2% is a useful guide although it is the type of organics that are more important than the amount mixture design should be used todetermine the levels that are acceptable for any particular site study and investigationThe site study will vary according to the stage at which soil Stabilisation is considered for the this is included at an early stage any relevant sources of information may be used,together with a site inspection to assess the practical information is available to specify the investigation and testing regimes to be used and reference should be made to HA(74) [5]If a site investigation has already been carried out certain useful information will already be available to assess the viability of soil Stabilisation to produce testing may be required especially regarding sulfate and organic is important to note that these elements are not usually uniformlydispersed within a soil and tend to get washed into lower testing is required to ensure that sulfur compounds are detected especially in areas of following points are relevant.

6 Carefully sample all areas to be cutting is to be carried out sample materials at the reduced level formation if cut material is to be treated take representatives samples of all parts of this mindful of the mixing that will take place during earthmoving operationsGroup materials into classes for more detailed testing may cause disruption and should be carefully monitored especially in cut for water-soluble sulfate,oxidisable sulfides and total potential sulfate should be carried content may hinder a Stabilisation process and should be content may vary widely depending on the whether these levels will change between the testing and actual site emphasis of site investigation should be to test materials in the laboratory that will be indicative of what will result on site after the earthworks investigation should be planned with reference to the latest version of HA74[5] and other relevant guidance [8].

7 Laboratory proceduresThe testing procedure carried out in the laboratory should reflect theprocedures that will be carried out on site as detailed procedures are detailed fully in HA74[5].The following describes thekey points and basic additions of additives are shown in Table using ggbs thehigher amounts of lime will be required to pulverize clays of higher plasticityand also to activate the systems also need the clay to be 1 Mixtures shall be prepared in a manner that reflects the time intervalbetween first and second stages mixing that will be achieved on shall be stored uncompacted between mixing stages in tightlysealed bags or containers and then stored for one hour after final mixingbefore strength specimens are shall be made that achieve final water contents corresponding OMC,OMC and shall be determined in accordance withthe Proctor method of BS1924[6].

8 For Cohesive mixtures it has been foundconvenient to compact mixtures at MCV s of 14,11 and 8 where generally avalue of 12 relates to OMC and 8 to the wettest value compatible withsatisfactory placement,compaction and OMC in thelaboratory shall be determined at a time after final mixing that relates tothe time of final compaction in the stage mixing shall be sufficient to achieve even distribution of limewithin the soil and shall contain sufficient water to fully hydrate all generally requires a soil with an MCV of 12 or second stage mixing,when cement or ggbs may be added,pulverisationmeasured in accordance with BS 1924 shall be in excess of 30% andmaterial retained on a sieve shall be less than 5%.Water may berequired to achieve an MCV of 12 or shall be tested for CBR and swell potential in accordance withSHW and is required to achieve a soaked CBR of not lessthan 15% after 7 days and an average swell of no more than 5mm or 10mmon any particular density of the treated and untreated Soils should be determined toassess any bulking heave tests should be carried out if the Capping will fall within thefrost heave treatment of Soils with Quicklime to produce Capping materialin accordance with highways agency specificationLimeGgbsCementLime - - 2% - - 11/11/05 9:57 am Page 1 datatechnicalBRITISH LIME Highways of Contract Documents for Highway for Highway Stationery Office,Norwich, Highways Manual for Roads and 7.

9 Pavement Design and - Foundations Lime Improvement using Technical Data Sheet No Products Association, et stabilization using lime-activated ground granulated blast furnace sixth CANMET/ACI International Conference Bangkok,Thailand Highways Manual for Roads and 4 Geothechnics and 1 of fill and Capping materials using lime or cement or :Part 2 materials for civil engineering of test for cement-stabilised and lime-stabilised Chiswick, Stabilisation Guidelines for Best ,Camberley, of Sulfate-Bearing Soils .Britpave,Camberley, LIME ASSOCIATIONG illingham House 38-44 Gillingham Street London SW1V 1 HUTel 020 7963 8000 Fax 020 7963 8001email cappingThe British Lime Association is one of the constituentbodies of the Quarry Products Association,the tradeassociation for the aggregate,asphalt and ready-mixedconcrete basic construction process consists of the following lime on the prepared formation using purpose made the soil and lime together with a may need to be added through spray bars in the mixer hood.

10 (Integrated machines are now available that will carry out spreading and mixing in one operation.)Lightly compact to seal the to to achieve pulverisation water if compact and trim to cement or ggbs are to be added this will be carried out after themellowing and remixing addition of lime to a Cohesive soil will cause a reduction in densityand some bulking to effect should be addressed at thelaboratory design stage to determine the slightly increased formationlevel after and moisture content are important factors in should be in accordance with content of the soil at all stages of construction is measuredvia the MCV test [6].Generally an upper limit of 12 ensures the mixtureis wet of optimum and that the binders have sufficient moisture forcomplete is crucial to achieve optimum final compaction a maximum MCV of 12 should be specified in orderto produce a Capping layer with minimal air is necessary tominimize moisture ingress that may lead to softening or thetransportation of water borne sulfates that may cause the case of sulfate/sulfide bearing Soils ,UK research [4]