A FLAC3D model of a raft foundation, multi-story building was used to assess the possibility of eliminating piles or jet-grouting columns from its initial design in favor of a thicker foundation. This would provide considerable savings in terms of costs, time, and site management.
A custom script was developed by HARPACEAS to convert midas GEN structural models into compatible FLAC3D structural elements (including all beams, shells, and plates - correctly interconnected - to simulate slabs, pillars, and floors connected with the raft foundation) with all acting loads (structural and non-structural dead loads and variable loads in SLS* quasi-permanent conditions).
For a correct estimation of settlements it was necessary to consider the stress path (lithostatic conditions, unloading due to excavation up to 8 m, and reloading up to maximum stress due to design loads considering the complete multi-story building). For this reason the Plastic Hardening soil model was applied.
The maximum settlement was predicted to be about 34 mm with negligible differential settlement. Negligible distortions and tilting were also predicted. Therefore, the thicker raft foundation, without piles or jet-grouting columns, was sufficient. The FLAC3D model was also validated by comparison with a "simplified" model based on the Boussinesq approach.
Thanks to the ability to import the midas GEN structural model into FLAC3D, it has been possible to consider its real stiffness which resulted in predictions of negligible differential settlements and significant cost savings.
*Note: SLS = Serviceability limit state
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