International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
Volume: 12 Issue: 01 | Jan 2025 www.irjet.net p-ISSN: 2395-0072
An Empirical study on Group Pile Settlement Based on Soil Structure Interaction
Vidhu Gopikrishnan1 , Benoy Benjamin2
1Assistant Professor, Dept. of Civil Engineering, College of Engineering and Management Punnapra, Alappuzha, Kerla, India
2Assistant Professor, Dept. of Civil Engineering, Cochin University College of Engineering, Kuttanad, Pulinkunnu, Alappuzha, Kerala, India ***
Abstract - Soil is a material of remarkable complexity and heterogeneity, characterized by a strong nonlinear response to external loading. Its behavior depends on coherence properties, saturation, and soil types, which throughout history caused varying constitutive laws designed to explain its behavior properties. An all-inclusive settlement formula for group piles has been developed with consideration of several contributing settlement factors. Such parameters include raft sizes, pile diameters, lengths and spacings, applied vertical pressures, soil modulus, ultimate pile-soil friction, and elastic modulus of the pile. An "influence coefficient" is presented as a way of measuring the influence each parameter has on settlement. The major players in settlement are the applied relatively uniform load, soil modulus, and raft dimensions, while pile diameter, length,andspacingaresecondaryfactors inthe mix.
Key Words: Mohr-Coulomb Model, Finite Element Method, Soil-Structure Interaction, Pile foundation, Frictionpile,
1.INTRODUCTION
Thestructuralfoundationsforbuildingsserveasthemain supportingsystemforthemfromabovegroundlevel.Most structural elements directly come in contact with the soil incivilengineering.Wherethesurfacesoildoesnothavea sufficient bearing capacity to support the loads of a structure, deep foundations are used to transmit these loads to deeper, stable soil strata. Friction piles rely on frictionalresistancedevelopedbetweenthesurfacesofthe pile against the soil around it, such as stiff clay or sandy soil, to resist loads adequately. The friction may develop along the full length or the toe portion of the pile, depending on soil stratification. Under friction pile systems, the entire surface of the pile will typically be involved in load transfer. Any analysis of settlement, whenever performed, would allow for the determination ofstabilityandperformanceofpilefoundations..
The entire pile group has been assumed to behave as a single entity in the assessment of its behavior, with the summation of base and shaft resistance ultimately determining its capacity. Under close spacing, the overall capacity of a group of piles is therefore more likely to
dependonthegroupperformanceofthepilesratherthan that of individual ones. The pile group settlement results from a combination of elastic shortening of the pile and that of the soil supporting it. It is generally assumed that thepilegroupactsasonedeepfoundation,likeapierora mat foundation. Total load on friction piles is, however, assumedtobeactingatadepthequaltotwo-thirdsofthe pile length. This block assumption is thus likely to overestimate the pile load capacity, rendering precise calculation of the settlement quite difficult. The effects of soil-structure interaction (SSI) can be incorporated into the calculations to improve settlement estimates, while a moreadvancedformulationforsettlementwillbederived fromtheanalysescarriedoutonANSYS.
Vidhu et al.[1] studied pile settlement behavior and loadcarryingcapacityataparticularspacingduetovariationof the L/d ratio of piles. The study finds that interaction between piles in a group tends to increase more with increasing L/d ratio, resulting in uneven load distribution wherein the outer piles take most of the load, sometimes leading to the initiation of plastic hinges. Also, for a pile group of constant dimensions, settlements under a given load remain almost unvaried over a practical range of spacings. Hence, smaller-diameter piles with larger spacing are preferred from a settlement viewpoint. Jalali et al. [2] studied pile-soil interaction and its effect on pile settlement and shear stress within the interaction zone. Using Mohr-Coulomb and Hard-Soil behavior laws, they found that under loading, the pie displacements were analyzed, where the Static Analysis of PLAXIS gives more reliable measures of settlement when the interface coefficients vary from 0.7 to 1 in the Mohr-Coulomb behaviorlawascomparedtotheHard-Soilmodel.Shaiana et al. [3] conducted numerical simulations in ABAQUS to investigate pile behavior embedded in cohesionless soil under oblique loads. Comparisons of various analysis procedures were made for single piles under different inclinations.Resultssuggestthatpilestiffnesshasastrong effect on its behavior under combined vertical and lateral (oblique) loading, where vertical and horizontal load levelsarehighlydependentontheangleofloadinclination (α). The additional horizontal load decreases the ultimate verticalpilecapacityofthepile.
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Volume: 12 Issue: 01 | Jan 2025 www.irjet.net
Johnson et al. [4] studied 3D finite element modeling to explore how factors like pile shape, sand characteristics, pile length, and loading conditions affect pile capacity. From the trends observed in these simulations, design charts were created to help to calculate the bearing capacity of square piles subjected to oblique loading. A thorough Finite element analysis showed that both sand properties and pile shape have a considerable impact on pilecapacity.
2.CREATION OF SETTLEMENT DATABASE FROM FINITE ELEMENT MODELS
Settlement formula is derived from the FE model configurations. The varying model parameters were basicallythewidth(wix), length(wiy)andthickness(th)of the rectangular raft, the diameter (di), length (Le) and spacing of the piles (Spx and Spy), the applied uniform load (Ld),thesoilmoduli(Es),theultimatepile-soilfriction(fr), and the elastic modulus of concrete (Ec). The input parametersareshowninTable.1
The analysis incorporated the Mohr-Coulomb (M-C) soil model, and a parametric study was conducted on its strength parameters, specifically friction angle and cohesion, to assess their relationship with settlement behavior.Thefindingsindicatedthattheseparametershad no direct influence on settlement, which is expected since group pile settlement does not occur in a failure state where soil strength parameters are crucial. Instead, deformations in group pile systems generally remain within the elastic range. Consequently, using a more advancedconstitutivemodelisnotconsiderednecessary.
Table -1: Theinputparameters
3.GENERAL SOLUTION FOR SETTLEMENT
The settlement dataset obtained from the finite element runsincludethevaluesofthesettlementatthecentre.The derivedsettlementformulaisgivenasfollows:
In this approach, S represents the calculated settlement, while SB denotes the base settlement in meters. The unitless fitting coefficients a, b, c, d, e, f, g, h, and i are used to refine the settlement formula. A dataset is obtained, consisting of both FE-based and formula-based settlement values, which have not yet been iterated or corrected. To quantify the accuracy of the formula, the squareddifferencebetweenthesetwosettlementvaluesis computed, defining the “error” for each data point. The total global error is then determined by summing all individual errors. The objective is to minimize this global error by adjusting the unitless coefficients. Using the "Solver" add-on in Excel, these coefficients are iteratively optimizedtoachievethebestpossiblefit.
Table – 2:UnitlessFittingCoefficient
Table -3: FittingConstantsofSettlementFormulawith Units.
A systematic procedure is employed to determine the exponential relationship of each individual input parameter on settlement [5]. In this approach, the influenceofaspecific parameterisisolatedwhilefiltering outtheeffectsofallotherparameters. Theprocessbegins by selecting a specific finite element (FE) model configuration as the baseline system. Next, variations of
International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
Volume: 12 Issue: 01 | Jan 2025 www.irjet.net p-ISSN: 2395-0072
this baseline model are created by modifying one input parameter at a time. For each modified configuration, the corresponding settlement is calculated, allowing for a clearassessmentoftheparameter’sindependentinfluence onsettlementbehavior.
The fitting constants such as u1, u4 and u7 are included in the terms in (…. + un)n format to enhance the fitting (R2) performanceof theformula.Usingsuchaconstantlikeu1 in a term enhances the fitting performance. The fitting constantssuchasu11,u12 andu15 areusedtonormalizethe termtheyareassociatedto.Inaddition,theR2 valueofthe formula is not affected from normalization. The elastic modulus of soil can be calculated as equivalent elastic modulus of all the soil layer. For large foundations the pressure bulb extents deep into the subsoil hence the estimation of equivalent Es for various soil layer into which the pressure bulb extends into is needed, the normal practice is to use a weighted average of the modulus of elasticity of the various layers encountered withinthedepthofinfluence
soils is influenced by pile length and diameter, soil properties, the spacing of pile groups, soil properties, loading conditions, as well as cost-effective and safe design. That is, an actual site of soil-structure interaction should find its way to the analysis and be considered therein
REFERENCES
[1] Vidhu Gopikrishnan, Deepa Varkey “A Comparative Study of Pile Settlement Analysis Based on Soil Structure Interaction,” International Research Journal ofEngineeringand Technology,vol.07,issue06,June 2020,pp.7520-7525,
[2] Mohammad Mahdi Jalali et.al, Using Finite Element Method For Pile-Soil Interface (Through PLAXIS And ANSYS),JournalOfCivilEngineeringAndConstruction TechnologyVol.3(10),November2012,Pp.256-272
[3] Dr. Hussein A Shaiaa, Dr. Sarmad A. Abbas, ThreeDimensional Analysis Response of Pile Subjected To Oblique Loads, International Journal Of Scientific & Engineering Research, Volume 6, February-2015, Issue2,
where,
Es =Equivalentmodulusofelasticity
Hi=Thicknessoflayer
Ei =Modulusofelasticityoflayer
This method of obtaining equivalent modulus of elasticity isacceptableaslongasthevariationofindividuallayersis comparable.
Substituting all the constants value to the general equation.
S= ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( )
4. CONCLUSIONS
This paper introduces a general group pile settlement formula that considers the effects of various parameters on settlement. The formula incorporates parameters such as the dimensions of a rectangular raft, pile diameter, length, spacing, applied vertical uniform pressure, soil moduli,ultimate pile-soil friction,and the elasticmodulus of the pile. An "influence coefficient" is introduced to quantify the contribution of each parameter. The most crucialfactorsaffectingthesettlementareapplieduniform load, soil modulus, and raft dimension, while the pile diameter,length,andspacinghavemoderateeffects.
Based on all these observations, it can therefore be concluded that the behavior of a pile group in cohesive
[4] Johnson, K. Et Al. (2006). Modelling the Load–Deformation Response Of Deep Foundations Under Oblique Loading. Environmental Modelling & Software,21(9),1375-1380.
[5] E. C. Levy (1959), Complex-curve fitting, IRE TransactionsonAutomaticControlVol:AC-4,Issue:1
[6] Mohd Ahmed, Mahmoud H. Mohamed, Javed Malik, Mohd Abul Hasan (2014), 3d Analysis of Soil Foundation Structure Interaction in Layered Soil, Open JournalofCivilEngineering,4,373-385
[7] Das, B., 1999. Principles of Foundation Engineering, fourthed.PWSPublishing,Melbourne.
[8] Bowles,J.(1997).FoundationAnalysisandDesign.5th Ed.,TheMcGraw-HillCompanies,Inc.,NewYork,308.