Advanced Design Optimization of Deep Foundations in Soft Saturated Clayey Soils according to Pressuremeter-based Methods using FOXTAv4: Application to Ganvié, Bénin

Abstract

Construction on the soft saturated soils of Ganvié, a lacustrine settlement on Lake Nokoué in Benin, requires deep foundations that can satisfy geotechnical capacity requirements while remaining compatible with restricted site access. This study evaluates and optimises a micropile solution for the Ganvié General Education College using Ménard pressuremeter and penetrometer data and the FONDPROF module of FOXTA v4 in accordance with NF P 94-262. The geotechnical profile comprises predominantly soft to moderately consistent clay layers extending to a depth of 25 m. The foundation response was assessed through limit-load calculations at the ultimate and serviceability limit states, with pile geometry and anchorage depth varied to identify a compliant solution. For the adopted profile, tip resistance was considered negligible because of the soft clay conditions, and the micropile therefore behaved as a floating element mobilising primarily shaft friction. The numerical analysis identified a type 2 bored micropile with a diameter of 250 mm and an anchorage depth of 15 m as the selected configuration. This solution provides a design capacity of 140 kN at the ultimate limit state and 98.5 kN at the serviceability limit state, reducing the required number of micropiles to 20 for the stated structural load. The results support pressuremeter-based depth optimisation as a practical approach for the studied site, while static load testing and group-effect verification remain advisable before construction.