Assessment of Analysis Techniques for Multi-Plate Anchors in Sand-Paper

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The study evaluates numerical methods for predicting the pullout capacity and stiffness of multi-plate anchors, such as helical anchors, in sand under vertical loading. Using axisymmetric models in OptumG2, it compares conventional limit analysis (LA), modified limit analysis (MLA), which reduces strength parameters to approximate sand’s non-associated behavior, and displacement-based elastoplastic finite element analysis (EP).<br /><br />A benchmarking study of single-plate anchors found that all three methods produced reasonable capacity estimates. LA matched prior numerical results, while MLA and EP were generally closer to published experimental data.<br /><br />The multi-plate analyses examined the effects of plate number and spacing. LA and MLA predicted essentially unchanged ultimate loads as these configurations varied. Their assumed associated flow and simplified failure mechanisms limit their ability to represent interactions between plates. EP captured more complex, localized failure around multiple plates, but its predictions were mesh-sensitive, with capacity variation reaching about 10%.<br /><br />In EP analyses, adding plates increased stiffness but unexpectedly reduced ultimate capacity. The authors note that this counterintuitive finding requires further investigation and experimental validation. Changing plate spacing produced broadly similar EP failure patterns and load-displacement responses.<br /><br />Overall, the study concludes that no method is fully reliable for all aspects of multi-plate anchor analysis. LA and MLA can offer useful estimates for single plates but struggle to model multi-plate behavior. EP better captures detailed failure mechanisms and stiffness, yet its mesh dependence, potentially unrealistic displacements, and other modeling assumptions require caution.

Keywords

multi-plate anchors

helical anchors

pullout capacity

stiffness prediction

vertical loading

sand behavior

limit analysis

elastoplastic finite element analysis

plate spacing

mesh sensitivity