This case study presents the geotechnical finite element analysis of a pile-raft foundation system supporting a high-rise residential building. The foundation comprises a 61 × 61 m² raft supported by 134 barrettes, as illustrated in Figure 1.

Figure 1: Footprint representation and barrettes layout

The barrettes are distributed across three groups:

• Type 1 located in the core area. Section 2800x1500 mm with a base at the level -77 m (69.7 m long).
• Type 2 positioned in the upper/right half of peripheral ring. Section 2800x1500 mm (same as type 1) with a base at the level -66.5 m (59.2 m long).
• Type 3 located in the lower/left half of peripheral ring. Section 2800x1000 mm with a base at the level -58 m (50.7 m long)

An important aspect of this study is the validation of the embedded beam modelling approach. This was addressed in a companion exercise entitled "Vertical Behaviour Assessment on an In-Group Barrette Pile", in which both volume piles and embedded beam piles were modelled and compared in a representative pile group configuration. The results of that study served to calibrate the embedded beam parameters used in the present model.

The main objective of this study is to build a comprehensive PLAXIS 3D geotechnical model to evaluate whether the foundation system satisfies serviceability limit state (SLS) criteria. Additionally, the model is used to provide meaningful geotechnical input to the structural design team. In particular, we focus on the derivation of equivalent spring stiffnesses that characterize the pile group behaviour and can be transferred to the structural model. This process highlights the iterative nature of geotechnical–structural interaction, where foundation stiffness from the geotechnical model feeds into the structural analysis, and loads from the structural model are fed back into the geotechnical simulation.

To streamline the model construction, an Excel-based automation process was used. One spreadsheet includes barrette geometries and locations, while another specifies pile head loads based on structural model outputs. These spreadsheets generate PLAXIS 3D command lines, significantly reducing model preparation time and ensuring consistency. This automation strategy will be showcased throughout the study.

Through this analysis, we also aim to demonstrate how a detailed geotechnical simulation, beyond regulatory compliance, can contribute meaningfully to multidisciplinary foundation design workflows.