International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
Volume: 13 Issue: 05 | May 2026 www.irjet.net p-ISSN: 2395-0072
LOAD–DEFORMATION BEHAVIOUR OF HYBRID GROUND-IMPROVED CLAY STRATA SUPPORTING SHALLOW FOOTING SYSTEMS
Punit Chaurasiya1 , Mr. Ushendra Kumar2
1Master of Technology, Civil Engineering, Lucknow Institute of Technology, Lucknow, India
2Head of Department, Department of Civil Engineering, Lucknow Institute of Technology, Lucknow, India
Abstract -The performance of shallow foundations on soft clay is often limited by low bearing capacity and excessive settlement, necessitating effective ground improvement techniques. This study investigates the load–deformation behaviour of hybrid ground-improved clay strata supporting shallow footing systems through a series of controlled laboratorymodeltests.Theresearchevaluatesandcompares the performance of untreated clay, soil improved with stone columns, geosynthetic reinforcement, and hybrid systems combining multiple techniques. Plate load tests were conducted to obtain load–settlement responses, from which key parameters such as bearing capacity, stiffness, and settlement characteristics were derived. The results indicate thatuntreatedclayexhibitshighcompressibilityandlowloadcarrying capacity, leading to significant deformation under loading.Individualimprovementtechniquesprovidemoderate enhancement; however, hybrid systems demonstrate substantialimprovementduetosynergisticeffects.Thehybrid ground improvement approach resulted in an increase in bearing capacity by approximately 2.5 to 4 times and a reduction in settlement of up to 50–60% compared to untreated soil. Additionally, the stiffness of the soil increased significantly, and the failure mechanism shifted from brittle punching shear to controlled and ductile deformation. The findings highlight the effectiveness of hybrid techniques in improving foundation performance and provide practical insights for the design of shallow foundations on weak clayey soils
Key Words: Hybrid ground improvement; Clay soil; Stone columns; Geosynthetic reinforcement; Load–settlement behaviour; Bearing capacity; Settlement reduction; Shallow foundations
1. INTRODUCTION
1.1 Background
1.1.1 Importance of Foundation Performance in Geotechnical Engineering
Foundationperformanceisacriticalaspectofgeotechnical engineering, as it governs the safety, stability, and serviceabilityofcivilengineeringstructures.Foundationsact astheprimaryinterfacebetweenthesuperstructureandthe supporting soil, ensuring that structural loads are safely transmitted to the ground without exceeding the soil’s bearingcapacityorcausingexcessivesettlement.Inadequate
foundation performance can lead to structural distress, differentialsettlement,tilting,orevencatastrophicfailure. Therefore,understandingtheinteractionbetweensoiland foundationsystemsisessential fordesigningefficientand economicalstructures.Parameterssuchasbearingcapacity, settlement, and stiffness play a vital role in evaluating foundation performance, particularly in weak soil conditions.
1.1.2 Challenges Posed by Soft Clay
Softclaysoilspresentsignificantchallenges in foundation engineeringduetotheirinherentlylowshearstrengthand highcompressibility.Thesesoilsareunabletosupportheavy loads without undergoing large deformations, leading to excessive settlement and long-term consolidation issues. Additionally, soft clays are highly sensitive to changes in moisturecontent,whichcan furtherreduce theirstrength andstiffness.Thepresenceofhighporewaterpressureand slowdrainagecharacteristicsmakestheirbehaviourtimedependent,complicatingdesignandanalysis.Thesefactors make soft clay deposits unsuitable for supporting shallow foundations without appropriate ground improvement measures.
1.1.3 Limitations of Shallow Foundations on Untreated Clay
Shallowfoundationsconstructedonuntreatedclayeysoils often suffer from poor performance due to inadequate bearing capacity and excessive settlement. The applied structuralloadstendtoinducelargeverticaldeformations, which may exceed permissible limits and affect structural integrity. Furthermore, failure mechanisms such as local shearorpunchingsheararecommonlyobservedinsoftclay, leading to unsafe conditions. The lack of stiffness in untreated clay results in a gradual and uncontrolled deformation pattern, making it difficult to predict failure accurately. These limitations highlight the necessity of improving the engineering properties of clay before the constructionofshallowfoundations.
1.2 Ground Improvement Techniques
1.2.1
Overview of Conventional Techniques
Ground improvement techniques are widely employed to enhance the engineering properties of weak soils, particularlysoftclay,tomakethemsuitableforconstruction.
International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
Volume: 13 Issue: 05 | May 2026 www.irjet.net p-ISSN: 2395-0072
Conventionalmethodsincludemechanicaltechniquessuch as stone columns and sand compaction piles, as well as chemicalstabilizationusinglimeorcement.Stonecolumns improveload-bearingcapacityanddrainagebyintroducing stiffgranularinclusionsinto thesoilmass,whilechemical stabilizationmodifiesthesoilstructure,reducingplasticity andincreasingstrength.Othermethods,suchaspreloading andconsolidation,areusedtoacceleratesettlementbefore construction. These techniques have been successfully applied in various geotechnical projects and provide noticeableimprovementsinsoilbehaviour.
1.2.2
Limitations of Individual Methods
Despitetheireffectiveness,individualgroundimprovement techniques often have limitations when applied to highly compressible and weak clay soils. For instance, stone columns may experience excessive lateral bulging in very softclay,reducingtheirload-carryingefficiency.Similarly, chemical stabilization alone may not adequately control deformation under higher loads, especially when the soil exhibitshighplasticity.Geosyntheticreinforcement,while effectiveinprovidingtensilestrength,maynotsignificantly improve deep soil layers. These limitations indicate that relying on a single technique may not provide sufficient improvement, particularly in challenging soil conditions, therebynecessitatingmoreadvancedapproaches.
1.3 Hybrid Ground Improvement Concept
1.3.1
Definition and Significance
Hybridgroundimprovementreferstothecombineduseof two or more ground improvement techniques to achieve enhancedsoilperformancecomparedtoindividualmethods. This approach integrates different mechanisms such as reinforcement, confinement, and stabilization to create a compositesoilsystemwithsuperiorstrengthandstiffness. The significance of hybrid systems lies in their ability to overcome the limitations of individual techniques by utilizing their combined advantages. Such systems are particularlybeneficialinsoftclayconditions,whereasingle methodmaynotbesufficienttomeetdesignrequirements. Hybridgroundimprovementhasgainedincreasingattention inrecentyearsduetoitseffectivenessandadaptability in complexgeotechnicalproblems.
1.3.2 Synergistic Mechanisms (Reinforcement + Confinement + Stabilization)
Theimprovedperformanceofhybridsystemsisprimarily attributed to the synergistic interaction of multiple mechanisms. Reinforcement, typically provided by geosyntheticsorfibers,introducestensilestrengthintothe soil,improvingloaddistributionandreducingdeformation. Confinement, achieved through elements such as stone columnsorgranularinclusions,restrictslateralexpansionof thesoilandenhancesitsshearstrength.Stabilization,using
chemicalagentslikelimeorcement,altersthesoilstructure andreduces plasticity,resultinginincreasedstiffnessand strength.Thecombinedactionofthesemechanismsleadsto amoreuniformstressdistribution,reducedsettlement,and enhanced load-carrying capacity, making hybrid systems highlyeffectiveforsupportingshallowfoundations.
1.4 Research Gap
1.4.1 Limited Studies on Hybrid Systems
Although ground improvement techniques have been extensively studied, research on hybrid ground improvement systems remains relatively limited. Most existingstudiesfocusonindividualmethodssuchasstone columns or geosynthetic reinforcement, with fewer investigations addressing their combined effects. The complexity of interaction between different improvement techniquesmakesitchallengingtodevelopacomprehensive understandingofhybridsystems.Asaresult,thereisaneed for systematic studies that explore the performance of combinedtechniquesundercontrolledconditions.
1.4.2 Lack of Load–Deformation Characterization
Another significant research gap is the lack of detailed characterization of load–deformation behaviour in hybrid ground-improved soils. While some studies report improvementsinbearingcapacityandsettlementreduction, thereislimitedinformationonhowthesesystemsbehave under progressive loading. Understanding the complete load–settlementresponse,includingstiffnessvariationand failure mechanisms, is essential for accurate design and analysis. The absence of such detailed characterization restricts the practical application of hybrid systems in engineeringprojects.
1.4.3 Insufficient Experimental Validation
Manyexistingstudiesonhybridgroundimprovementrely heavilyonnumericalsimulations,withlimitedexperimental validation. Laboratory model tests and field studies are essentialtoverifytheoreticalpredictionsandtocapturereal soil behaviour under loading. However, the availability of suchexperimentaldataislimited,particularlyfordifferent combinations of improvement techniques. This lack of validation creates uncertainty in design and limits confidenceintheapplicationofhybridsystems.Therefore, comprehensiveexperimentalinvestigationsarerequiredto bridge this gap and provide reliable data for engineering practice.
International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
Volume: 13 Issue: 05 | May 2026 www.irjet.net p-ISSN: 2395-0072
2. LITERATURE REVIEW
2.1 Behavior of Soft Clay
2.1.1 Load
–Settlement Characteristics
Soft clay exhibits a highly nonlinear load–settlement responseduetoitslowstiffnessandhighcompressibility.At initialstagesofloading,thesettlementincreasesgradually with applied load, representing an elastic or near-elastic response. However, as the load increases, the rate of settlementacceleratessignificantly,indicatingtheonsetof plasticdeformation.Unlikegranularsoils,softclaydoesnot typicallyshowadistinctpeakintheload–settlementcurve; instead, it undergoes continuous deformation with increasingload.Thisbehaviourisfurtherinfluencedbytimedependent consolidation, where the dissipation of excess pore water pressure leads to additional settlement over time.Theoverallresponsehighlightsthepoorload-carrying capacityandhighdeformabilityofuntreatedclay,makingit unsuitable for supporting foundations without improvement.
2.1.2
Failure Mechanisms (General, Local, Punching Shear)
Thefailuremechanismofsoftclayunderloadingdependson itsconsistencyandstrength.Inrelativelystiffclays,general shear failure is observed, characterized by well-defined failure surfaces and noticeable heaving of soil around the footing. In medium consistency clays, local shear failure occurs, where the failure surfaces are partially developed anddeformationismoregradual.Inverysoftclays,punching shearfailureisdominant,wherethefootingpenetratesinto the soil with minimal lateral displacement, resulting in excessive settlement. This type of failure is particularly criticalasitoccurswithoutclearwarning,posingariskto structuralstability.Understandingthesefailuremechanisms is essential for evaluating foundation performance and selectingappropriategroundimprovementtechniques.
2.2 Stone Columns
2.2.1
Mechanism and Performance
Stone columns are widely used ground improvement elements that consist of vertical inclusions of compacted granular material installed within soft soil. Their primary functionistoenhancetheload-bearingcapacityandreduce settlementbyactingasstiffinclusionswithintheweaksoil matrix. The mechanism of improvement involves load transferfromthesurroundingsoiltothestonecolumnsdue totheirhigherstiffness,resultinginstressconcentrationon thecolumns.Additionally,stonecolumnsprovidedrainage paths that accelerate consolidation by facilitating the dissipation of excess pore water pressure. Studies have shownthatstonecolumnscansignificantlyincreasebearing
capacity and reduce settlement, making them an effective solutionforimprovingsoftclaydeposits.
2.2.2 Limitations (Bulging, Efficiency in Soft Clay)
Despite their advantages, stone columns have certain limitations,particularlyinverysoftclayconditions.Oneof the major issues is lateral bulging, where the column materialexpandsoutwardduetoinsufficientconfinement from the surrounding weak soil. This reduces the loadcarrying efficiency of the columns and may lead to premature failure. Additionally, the effectiveness of stone columnsdependsonparameterssuchasspacing,diameter, andlength,whichrequirecarefuloptimization.Inextremely softsoils,theimprovementachievedmaybelimitedunless additionalreinforcementorconfinementisprovided.These limitationshighlighttheneedforenhancedtechniques,such asencasementorhybridsystems,toimproveperformance.
2.3 Geosynthetic Reinforcement
2.3.1 Role of Geogrids/Geotextiles
Geosyntheticmaterials,includinggeogridsandgeotextiles, are widely used in ground improvement to enhance the mechanical behaviour of soils. These materials provide tensilestrength,whichnaturalsoilslack,andaretypically placedwithinorabovethesoiltoreinforceit.Geogrids,with their open grid structure, interlock with soil particles and improve load transfer, while geotextiles act as separation and reinforcement layers. When used beneath shallow foundations,thesematerialshelpindistributingtheapplied load over a wider area, thereby reducing stress concentrationandimprovingoverallstability.Theireaseof installationandadaptabilitymakethemapopularchoicein geotechnicalapplications
2.3.2 Improvement in Stiffness and Load Distribution
The inclusion of geosynthetic reinforcement leads to a significant improvement in soil stiffness and load distribution characteristics. By providing confinement, geosynthetics restrict lateral deformation of the soil, resulting in increased resistance to compression. This enhancesthestiffnessofthesoilmass,whichisreflectedina steeperload–settlementcurve.Additionally,reinforcement layersdistributetheappliedloadmoreuniformlyacrossthe soil, reducing localized stress and minimizing settlement. Experimentalstudieshavedemonstratedthatgeosyntheticreinforced soils exhibit improved bearing capacity and reduced deformation compared to untreated soil, making themeffectiveforfoundationsupport.
International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
Volume: 13 Issue: 05 | May 2026 www.irjet.net p-ISSN: 2395-0072
2.4 Hybrid Ground Improvement
2.4.1 Stone Column + Geogrid Systems
Hybrid systems combining stone columns with geogrid reinforcementrepresentanadvancedgroundimprovement approach.Insuchsystems,stonecolumnsprovidevertical load-bearing capacity and drainage, while geogrids offer lateral confinement and improved load distribution. The geogrid layers are typically placed above or around the columns,enhancingtheirperformancebyrestrictingbulging andincreasingstability.Thiscombinationresultsinamore efficientloadtransfermechanismandsignificantlyimproved bearing capacity. Studies have shown that such hybrid systems outperform conventional stone columns, particularlyinsoftclayconditions.
2.4.2 Stabilized Soil + Fiber Systems
Anotherformofhybridgroundimprovementinvolvesthe combination of chemical stabilization with fiber reinforcement. Stabilizing agents such as lime or cement improvethestrengthandreducetheplasticityofclay,while discrete fibers provide tensile resistance and enhance ductility. The fibers help in bridging soil particles and preventing crack propagation, resulting in improved deformation behaviour. This combination leads to a more stable and durable soil mass with higher strength and reducedsettlement.Suchsystemsareparticularlyusefulin highlyplasticclayswherebothstrengthenhancementand deformationcontrolarerequired.
2.4.3 Previous Experimental Findings
Previous experimental studies on hybrid ground improvement systems have consistently demonstrated significant improvements in soil performance. Results indicatethathybridsystemscanincreasebearingcapacity bymultiple timescompared tountreatedsoilandachieve substantial reduction in settlement. The load–settlement curvesforhybridsystemstypicallyshowhigherstiffnessand delayed failure, indicating improved resistance to deformation. However, the extent of improvement varies depending on factors such as configuration, material properties, and geometric parameters. Despite promising results, the available experimental data is still limited, necessitatingfurtherresearch.
2.5 Load–Deformation Behaviour
2.5.1
Stress Distribution
Theload–deformationbehaviourofimprovedsoilislargely governedbythedistributionofstresswithinthesoilmass.In untreated clay, the applied load is distributed unevenly, leading to high stress concentration and excessive settlement. In contrast, improved systems facilitate more uniformstressdistributionbytransferringaportionofthe
load to stiffer elements such as stone columns or reinforcement layers. This redistribution reduces the intensityofstressactingontheweaksoil,therebyimproving overall performance. Effective stress distribution is a key factor in enhancing bearing capacity and controlling settlement.
2.5.2 Composite Action
Compositeactionreferstothecombinedbehaviourofsoil and improvement elements acting as a single integrated system. In hybrid ground improvement, different components such as soil, columns, and reinforcement interacttosharetheappliedload.Thisinteractionleadsto improvedstiffness,strength,anddeformationcharacteristics compared to individual components acting alone. The composite system exhibits enhanced resistance to deformation and a more controlled failure mechanism. Understanding this composite behaviour is essential for accurately predicting the performance of hybrid groundimproved soil and for optimizing design in practical applications.
3. MATERIALS AND METHODS
3.1 Methodological Framework
3.1.1
Experimental Approach
The present study adopts a systematic experimental approachtoinvestigatetheload–deformationbehaviourof clayeysoilunderdifferentgroundimprovementconditions. Laboratory model tests are conducted under controlled conditionstosimulatetheresponseofshallowfoundations resting on untreated and improved soil. This approach allowsprecisecontrolovervariablessuchassoilproperties, moisturecontent,andloadingconditions,ensuringreliable and repeatable results. The experimental methodology focuses on generating load–settlement data through plate loadtests,whichserveastheprimarybasisforevaluating bearing capacity, settlement behaviour, and stiffness characteristicsofthesoil.
3.1.2
Comparative Testing Strategy
A comparative testing strategy is employed to assess the effectiveness of various ground improvement techniques. Thestudyincludesfourdistincttestconditions:untreated clay,clayimprovedwithstonecolumns,clayreinforcedwith geosynthetics, and a hybrid system combining multiple techniques. By maintaining consistent testing conditions acrossallcases,theinfluenceofeachimprovementmethod canbeisolatedandevaluated.Thiscomparativeframework enablesaclearunderstandingoftherelativeperformanceof individual and hybrid systems in terms of load-carrying capacityanddeformationbehaviour.
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3.2 Materials
3.2.1 Clay Soil
3.2.1.1
Classification (CH Soil)
Thesoilusedinthisstudyisclassifiedashighplasticityclay (CH)accordingtostandardsoilclassificationsystems.Such soilsarecharacterized byhighcompressibility,significant plasticity, and low shear strength, making them representativeofproblematicsubsoilconditionscommonly encounteredinpractice.TheselectionofCHsoilensuresthat thestudyeffectivelycapturesthechallengesassociatedwith weak clay deposits and highlights the need for ground improvement.
3.2.1.2 Index and Engineering Properties
The engineering behaviour of the clay soil is determined through standard laboratory tests, including Atterberg limits, compaction characteristics, shear strength, and consolidation properties. These tests provide essential parameterssuchasliquidlimit,plasticlimit,plasticityindex, optimum moisture content (OMC), and maximum dry density (MDD). The results indicate that the soil has high plasticityandcompressibility,withrelativelylowundrained shear strength, making it highly susceptible to settlement under loading. These properties form the baseline for evaluating the effectiveness of ground improvement techniques.
3.2.2 Ground Improvement Materials
3.2.2.1
Stone Aggregates
Stone aggregates are used for constructing stone columns within the clay soil. These aggregates typically consist of crushed stones of suitable size, providing high strength, stiffness,andpermeability.Theirprimaryfunctionistoact as load-bearing inclusions and facilitate drainage, thereby improving the overall performance of the soil. The use of stone aggregates enhances the bearing capacity and accelerates consolidation by allowing rapid dissipation of porewaterpressure.
3.2.2.2
Geosynthetics
Geosyntheticmaterials,suchasgeogridsorgeotextiles,are usedasreinforcementelementsinthesoil.Thesematerials provide tensile strength and improve load distribution within the soil mass. When placed at appropriate depths, geosynthetics enhance confinement, reduce lateral deformation, and increase the stiffness of the soil. Their inclusion is particularly effective in soft clay conditions, wherenaturalsoillackstensileresistance.
3.2.2.3
Stabilizing Agents
Chemicalstabilizingagents,suchaslimeorcement,areused toimprovethestrengthandreducetheplasticityofclaysoil. These agents react with the soil to form cementitious compounds, which enhance inter-particle bonding and increase stiffness. Stabilization helps in reducing compressibility and improving long-term performance, making the soil more suitable for supporting structural loads.
3.3 Experimental Program
3.3.1
Test Matrix
Theexperimentalprogramisstructuredusingapredefined test matrix that includes different soil conditions for comparative analysis. Four test cases are considered: T1 represents untreated clay as the reference condition; T2 involves clay improved with stone columns; T3 includes geosyntheticreinforcement;andT4representsthehybrid ground improvement system. This structured approach ensures systematic evaluation of each improvement technique and facilitates direct comparison of their performance.
3.4 Model Preparation
3.4.1
Soil Bed Preparation
3.4.1.1 OMC, MDD, Compaction
Procedure
The soil bed is prepared at its optimum moisture content (OMC) to achieve maximum dry density (MDD), ensuring uniform and consistent soil conditions. The clay is thoroughlymixedwithwaterandcompactedinlayerswithin atesttank.Eachlayeriscompactedtoachieveahighdegree ofcompaction,minimizingvoidsandensuringhomogeneity throughout the soil mass. This procedure is essential for obtainingreliableandreproducibleexperimentalresults.
3.4.1.2 Layering Technique
Thesoilisplacedinmultiplelayersofuniformthicknessand compacted sequentially. This layered approach ensures consistent density and reduces variability within the soil bed. The total thickness of the soil bed is maintained sufficientlylargetoavoidboundaryeffectsandtosimulate realisticstressdistributionbeneaththefooting.
3.4.2 Installation of Improvement Techniques
3.4.2.1
Stone Column Installation
Stone columns are installed using a replacement method, where soil is removed from designated locations and replacedwithcompactedstoneaggregates.Thecolumnsare constructed in layers to ensure proper compaction and
International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
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stability.Theirspacinganddiameterarecarefullycontrolled toachieveeffectiveloaddistribution.
3.4.2.2 Reinforcement Placement
Geosyntheticreinforcementisplacedhorizontallywithinthe soilatspecifieddepthsbelowthefooting.Thereinforcement layers are extended beyond the footing area to ensure properanchorageandeffectiveloadtransfer.Thisplacement enhancesconfinementandimprovesloaddistribution.
3.4.2.3 Hybrid Configuration
In the hybrid system, stone columns and geosynthetic reinforcement (and/or stabilized soil) are combined to create a composite ground improvement system. The configurationisdesignedtomaximizeinteractionbetween different components, resulting in improved strength, stiffness,anddeformationbehaviour.
3.5 Model Footing and Loading Setup
3.5.1 Footing Details (Geometry and Material)
Themodelfootingusedinthestudyistypicallyarigidsteel plate of square or circular shape. The dimensions are selectedtoensureproperstressdistributionwithinthesoil bedwhileminimizingboundaryeffects.Therigidnatureof thefootingensuresthatmeasuredsettlementcorrespondsto soildeformationonly.
3.5.2 Loading System (Hydraulic Loading, Measurement Instruments)
Ahydraulicjackisusedtoapplyverticalloadonthefooting in a controlled manner. The load is transferred through a loadingframetoensurestabilityandalignment.Settlement ismeasuredusingdialgaugesordisplacementsensorswith highprecision.Theinstrumentationsetupensuresaccurate recordingofloadandcorrespondingdeformation.
3.6 Testing Procedure
3.6.1 Plate Load Test Methodology
The plate load test is conducted to evaluate the load–settlementbehaviourofthesoil.Arigidplateisplacedonthe preparedsoilsurface,andloadisappliedincrementally.The correspondingsettlementisrecordedateachstage,allowing thedevelopmentofload–settlementcurves.
3.6.2 Loading Increments
Theloadisappliedinequalincrements,typicallyafraction oftheestimatedultimateload.Eachincrementismaintained for a sufficient duration to allow settlement stabilization before the next load is applied. This ensures accurate measurementofsoilresponse.
3.6.3
Observation Intervals
Settlementreadingsarerecordedatregulartimeintervals after each load increment. These intervals capture both immediateandtime-dependentsettlementbehaviour,which is particularly important for clayey soils exhibiting consolidationeffects.
4. RESULTS
4.1 Soil Properties
4.1.1
Baseline Characteristics
The baseline properties of the clay soil establish the reference condition for evaluating the effectiveness of ground improvement techniques. The soil is classified as highplasticityclay(CH),characterizedbyhighliquidlimit, significant plasticity index, low undrained shear strength, andhighcompressibility.Thesepropertiesindicatethatthe soil is weak and susceptible to large deformation under loading.Theconsolidationcharacteristicsfurtherconfirmits time-dependent settlement behaviour due to slow dissipationofporewaterpressure.Suchbaselineconditions justifytheneedforimprovementandprovideabenchmark againstwhichtheperformanceoftreatedsoilsisassessed.
4.2 Load–Settlement Behaviour
4.2.1 Untreated Clay
Theload–settlementbehaviourofuntreatedclayexhibitsa highly nonlinear response, reflecting its low stiffness and poorload-bearingcapacity.Evenatrelativelylowloadlevels, significant settlement is observed, indicating high compressibility.Theload–settlementcurveshowsagradual increasewithoutaclearpeak,suggestingprogressivefailure typical of soft clay. The absence of sufficient resistance to deformationleadstoexcessivesettlement,makinguntreated clay unsuitable for supporting shallow foundations under moderatetoheavyloads.
4.2.2 Stone Column Improved Soil
The inclusion of stone columns significantly enhances the load–settlement response of the soil. The curve becomes steeper in the initial stages, indicating increased stiffness and improved resistance to deformation. Settlement is noticeablyreducedcomparedtountreatedclay,asthestone columnsactasload-bearinginclusionsandfacilitatebetter stress distribution. Additionally, the improved drainage conditionsaccelerateconsolidation,furtherreducinglongterm settlement. However, the improvement is moderate and depends on parameters such as column spacing and diameter.
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4.2.3 Geosynthetic Reinforced Soil
Geosyntheticreinforcementimprovestheload–settlement behaviourbyprovidingtensilestrengthandconfinementto the soil mass. The reinforced soil exhibits reduced settlement and enhanced stiffness compared to untreated conditions.Theload–settlementcurvedemonstratesamore controlled deformation pattern, with lower settlement values across all load levels. The reinforcement helps distributetheappliedloadoverawiderareaandrestricts lateral deformation, thereby improving overall soil performance.
4.2.4 Hybrid Improved Soil
Thehybridgroundimprovementsystemdemonstratesthe mostsignificantenhancementinload–settlementbehaviour. The load–settlement curve is considerably steeper, indicating a substantial increase in stiffness and loadcarrying capacity. Settlement is greatly reduced even at higherloadlevels,andfailureisdelayedcomparedtoother conditions. The combined effect of reinforcement, confinement, and stabilization results in a highly efficient composite system. This behaviour confirms the superior performanceofhybridtechniquesincontrollingdeformation andimprovingfoundationsupport.
4.3 Comparative Performance
4.3.1 Bearing Capacity Comparison (BCR Evaluation)
Thecomparativeanalysisofbearingcapacityhighlightsthe progressive improvement achieved through different techniques. Untreated clay exhibits the lowest bearing capacityduetoitsweak nature.Theintroductionofstone columnsresultsinamoderateincrease,whilegeosynthetic reinforcementfurtherenhancesload-carryingcapacity.The hybridsystemshowsthehighestimprovement,withbearing capacity increasing by approximately 2.5 to 4 times comparedtountreatedsoil.Thisimprovementisquantified using the Bearing Capacity Ratio (BCR), which clearly demonstrates the effectiveness of hybrid ground improvementinenhancingsoilstrengthandstability.
4.3.2 Settlement Reduction (SRR Comparison)
Settlement reduction is another critical parameter for evaluating foundation performance. Untreated clay shows thehighestsettlementduetoitshighcompressibility.The use of stone columns reduces settlement by improving stiffness and drainage, while geosynthetic reinforcement provides additional reduction through confinement. The hybridsystemachievesthemaximumreduction,typicallyin therangeof50–60%,duetothecombinedactionofmultiple improvementmechanisms.TheSettlementReductionRatio (SRR)effectivelyquantifiesthisimprovement,highlighting thesuperiorperformanceofhybridsystemsincontrolling deformation.
4.4 Load–Deformation Characteristics
4.4.1 Stiffness Improvement
Stiffnessimprovementisevidentfromtheslopeoftheload–settlementcurveintheinitialloadingstages.Untreatedclay exhibitslowstiffness,resultinginlargedeformationunder small loads. The introduction of stone columns increases stiffness by providing rigid inclusions, while geosynthetic reinforcement further enhances it by restricting lateral deformation.Thehybridsystemshowsthehigheststiffness improvement, typically ranging from 3 to 5 times that of untreatedsoil.Thisincreasedstiffnessleadstobetterload distribution and reduced settlement, contributing to improvedfoundationperformance.
4.4.2 Failure Mechanism Transition
Theapplicationofgroundimprovementtechniquesresults inasignificanttransitioninfailuremechanisms.Untreated clay primarily exhibits punching or local shear failure, characterized by excessive settlement and limited lateral resistance. With the introduction of stone columns and geosynthetics,thefailuremodeshiftstowardsgeneralshear failure, which is more stable and involves better load distribution. In hybrid systems, the failure mechanism further evolves into controlled and ductile deformation, wherethesoilundergoesgradualsettlementwithoutsudden collapse.Thistransitionenhancesthesafetyandreliabilityof thefoundationsystembyprovidingwarningbeforefailure andpreventingabruptstructuraldamage.
5.CONCLUSION
Thisstudyinvestigatedtheload–deformationbehaviourof hybrid ground-improved clay strata supporting shallow footing systems through controlled laboratory experimentation. The results demonstrate that untreated clayexhibitslowbearingcapacity,highcompressibility,and excessive settlement, making it unsuitable for supporting shallowfoundationswithoutimprovement.Theapplication ofindividualgroundimprovementtechniques,suchasstone columnsandgeosyntheticreinforcement,providesmoderate enhancement by increasing stiffness and improving load distribution.However,themostsignificantimprovementis achieved through hybrid ground improvement systems, whichcombinemultipletechniquestoproduceasynergistic effect.
Thehybridsystemsshowasubstantialincreaseinbearing capacity, typically ranging from 2.5 to 4 times that of untreated soil, along with a settlement reduction of approximately 50–60%. The load–settlement response of hybrid-improved soil indicates higher initial stiffness and delayed failure, reflecting improved resistance to deformation.Additionally,thefailuremechanismtransitions frombrittlepunchingshearinuntreatedclaytocontrolled and ductile deformation in hybrid systems, enhancing
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structural safety. The comparative analysis confirms that hybrid techniques outperform individual methods due to improved stress distribution and composite action within thesoilmass.
Overall, the findings highlight the effectiveness of hybrid ground improvement in enhancing the performance of shallow foundations on weak clayey soils. The study providesvaluableinsightsforpracticalgeotechnicaldesign and supports the adoption of hybrid techniques in challengingsoilconditions.
6.FUTURE SCOPE OF RESEARCH
Futureresearchshouldfocusonextendingthepresentstudy throughlarge-scalefieldinvestigationstovalidatelaboratory findings and address scale effects. Advanced numerical modellingtechniques,suchasfiniteelementanalysis,canbe employed to simulate complex soil–structure interactions andevaluatetheinfluenceofvariousparameters,including columnspacing,depth,andreinforcementconfiguration.The behaviour of hybrid systems under dynamic and cyclic loading conditions, such as seismic or machine-induced loads, should also be investigated to enhance their applicabilityinreal-worldscenarios.Additionally,long-term performancestudiesconsideringconsolidation,creep,and durability of materials are essential. The development of simplifieddesignguidelinesandempiricalmodelsbasedon extensive experimental data would further facilitate the practical implementation of hybrid ground improvement techniques.
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