Estimation of Equivalent Stiffness of Pile Groups in Piled Raft Foundations Using Numerical Methods and Introduction of a Transfer Approach to Structural Modeling in SAFE

Subject Areas : Structural Mechanics

Ali Mahdizadeh ^{1 *} , MAHDI MOMENI REGHABADI ^{2 *} , ramin tabatabai ^{3 *}

1 - Ph.D. Candidate in Civil Engineering, Department of Civil Engineering, Islamic Azad University, Kerman, Iran
2 - Assistant Professor of Civil Engineering, Department of Civil Engineering, Islamic Azad University, Kerman, Iran
3 - Assistant Professor of Civil Engineering, Department of Civil Engineering, Islamic Azad University, Kerman, Iran

Received: 2025-07-27 Accepted : 2025-08-24 Published : 2025-05-21

Keywords: Equivalent Stiffness, Piled Raft Foundation, Numerical Analysis, Settlement, Soil-Structure Interaction, SAFE Software, PLAXIS 3D,

Abstract :

In the design of piled raft foundations, capturing the complex interaction between soil piles, and raft is essential, as this system benefits from the combined bearing capacity of both components. However, one major challenge in practical applications is estimating the equivalent stiffness of the pile group for use in structural software such SAFE,which lacks the ability to model real soil behavior accurately and instead relies on simplified spring elements. This limitation can result in significant discrepancies in predicting foundation performance.This study employs 3D numerical modeling in PLAXIS to analyze the behavior of pile groups in composite foundations under static loading. Various configurations, including square, radial and symmetric pile arrangements, are examined across different soil types and pile geometries. The equivalent stiffness values are derived using multiple criteria, such as allowable settlement, a defined percentage of the ultimate load (typically 40%)and average settlement at key foundation points.A practical method is proposed to transfer these stiffness values into the SAFE environment by defining equivalent spring systems beneath the structural slab. This approach enables designers to reflect actual soil–foundation behavior within a structural model without performing full geotechnical simulations. The effects of pile length, spacing-to-diameter ratio, soil stiffness, and loading pattern on the resulting equivalent stiffness are also investigated.The findings demonstrate that accurate estimation and proper implementation of equivalent stiffness in structural modeling significantly improve the reliability of piled raft foundation design.This method offers a valuable tool for engineers seeking to optimize structural performance in complex geotechnical conditions

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