Anchor screws, also known as helical piles, are being considered as foundation systems for temporary structures installed in coastal areas. The main objective of this study is to propose a design model suitable for piles subjected to both tensile and compressive loads in water-saturated soils. Existing studies have predominantly focused on dry environments and tensile forces. Small-scale experimental tests were conducted to identify the principal geometric parameters and to assess the impact of soil characteristics on the axial resistance of the piles. The results show that, regardless of the geometric variations of the piles, the ratio of resistances in dry and saturated environments remains relatively constant. The presence of water reduces the soil's bearing capacity, with the effective unit weight being a degrading factor. Image correlation analyses revealed the formation of a truncated cone-shaped failure zone: above the helix in tension, and below it in compression. For multi-helix piles, both independent and coupled failure modes were observed depending on the spacing between helices. A transition criterion between these behaviors was identified for a spacing-to-helix diameter ratio equal to 3. These observations were confirmed through numerical modeling. Based on this, analytical design models were developed: one primarily derives its capacity from the self-weight of the soil above the helix in tension, and the other from end-bearing resistance in compression. These models were compared against full-scale tests and existing models in the literature. They show good agreement in both tension and compression for single-helix piles, but require improvement for multi-helix piles under compression. Despite these limitations, the findings support the potential use of sand screws as an efficient, cost-effective, and low-environmental-impact foundation solution that meets the requirements for temporary structures in coastal areas.
- Contribution à l'étude des pieux hélicoïdaux pour la fondation de structures temporaires en milieu maritime
- Jeanne Naby - Structures Innovantes, Géomatériaux, ECOconstruction
- Jérôme QuirantMoulay Saïd El Youssoufi [Président]Mahdia Hattab [Rapporteur]Pierre Breul [Rapporteur]Julien AversengVincent Richefeu
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