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<p>Soil Structure Interaction (SSI) plays a central role in the design of raft foundations, particularly for buildings in which settlement compatibility and internal force distribution govern structural safety and economy. However, in routine foundation design practice, the interaction between the soil, foundation, and superstructure is often simplified. In many analyses, the stiffness of the superstructure is neglected and its influence is represented through applied shear wall or column loads, an assumption that may be inappropriate for rigid, shear wall–dominated building systems such as tunnel-form structures. This study presents a three-dimensional finite element assessment of SSI for a representative G + 14 tunnel-form building with a total height of 43.2&#xa0;m, founded on dry sandy soil and supported by a 0.60&#xa0;m thick raft foundation. Using PLAXIS 3D, two modeling approaches: a conventional raft on soil system subjected to applied shear wall loads model and an integrated model incorporating full superstructure stiffness are compared across a range of sand densities and constitutive models. Results demonstrate that neglecting superstructure stiffness leads to substantial inconsistencies in foundation bending moment predictions, with midspan moments decreasing by up to 83% as soil relative density increases from 20% to 90%, while support moments rise from negligible values to over 140 kNm/m, producing unrealistic tensile zone reversals and reinforcement demands. Moreover, the bending moment is highly sensitive to the soil constitutive model, with the simplified SSI model producing large discrepancies between the Hardening Soil, Mohr–Coulomb, and Linear Elastic model, including significant magnitude differences and even reversal of moment sign in certain regions of the raft. In contrast, explicit inclusion of superstructure rigidity shows limited sensitivity to soil density (&lt; 10–15%) and constrains variations due to constitutive models to 10–20%, resulting in physically consistent bending moments and coherent reinforcement patterns.</p>

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Effect of Soil-Structure Interaction on Raft Foundation Design: A 3d Finite Element Study of Tunnel-Form Buildings on Dry Sandy Soil

  • 期刊论文

  • 发表日期：

    2026年7月7日

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  • Sid Ali Rafa,
  • Mohammed Ilyes Benkraled,
  • Mohamed Annad,
  • Idriss Rouaz

摘要

Soil Structure Interaction (SSI) plays a central role in the design of raft foundations, particularly for buildings in which settlement compatibility and internal force distribution govern structural safety and economy. However, in routine foundation design practice, the interaction between the soil, foundation, and superstructure is often simplified. In many analyses, the stiffness of the superstructure is neglected and its influence is represented through applied shear wall or column loads, an assumption that may be inappropriate for rigid, shear wall–dominated building systems such as tunnel-form structures. This study presents a three-dimensional finite element assessment of SSI for a representative G + 14 tunnel-form building with a total height of 43.2 m, founded on dry sandy soil and supported by a 0.60 m thick raft foundation. Using PLAXIS 3D, two modeling approaches: a conventional raft on soil system subjected to applied shear wall loads model and an integrated model incorporating full superstructure stiffness are compared across a range of sand densities and constitutive models. Results demonstrate that neglecting superstructure stiffness leads to substantial inconsistencies in foundation bending moment predictions, with midspan moments decreasing by up to 83% as soil relative density increases from 20% to 90%, while support moments rise from negligible values to over 140 kNm/m, producing unrealistic tensile zone reversals and reinforcement demands. Moreover, the bending moment is highly sensitive to the soil constitutive model, with the simplified SSI model producing large discrepancies between the Hardening Soil, Mohr–Coulomb, and Linear Elastic model, including significant magnitude differences and even reversal of moment sign in certain regions of the raft. In contrast, explicit inclusion of superstructure rigidity shows limited sensitivity to soil density (< 10–15%) and constrains variations due to constitutive models to 10–20%, resulting in physically consistent bending moments and coherent reinforcement patterns.