Three-Dimensional Soil-Structure Interaction Analysis of Top-Down Basement Excavation in Jakarta Soft Soil Condition Considering Numerical Instability

Abstract

Basement construction in dense urban areas with soft clay deposits requires excavation support system capable of controlling ground deformation and retaining structure responses during staged excavation. This study evaluates the behavior of a top-down excavation system in Jakarta soft clay using three-dimensional finite element modelling with a soil–structure interaction approach. The numerical model was conducted using MIDAS GTS NX and consisted of soil layers, a diaphragm wall, ring slabs, a raft foundation, kingposts, bored piles, and soil–structure interface elements. The soil was modeled using the Hardening Soil Model, while the structural components were modeled as linear elastic elements. Soil parameters were interpreted from borehole data, Standard Penetration Test results, Cone Penetration Test results, and laboratory tests. The results show that the lateral displacement of the diaphragm wall increased with excavation depth due to the release of lateral earth pressure on the excavated side. A fully converged response was obtained up to the Basement 3 excavation stage, with a maximum diaphragm wall displacement of 9.77 mm, corresponding to approximately 0.10% of the excavation depth. The representative vertical displacement section showed a surface settlement of approximately 6 mm and an upward movement of approximately 16 mm at the excavation base, indicating a basal heave tendency without confirmed basal failure. Principal stress and maximum shear stress distributions showed stress concentrations around ring slab elevations, slab openings, and diaphragm wall corners. These results indicate that the ring slabs acted not only as floor elements but also as lateral restraint members that contributed to stress redistribution and wall deformation control. The subsequent excavation stage experienced numerical non-convergence, which was interpreted as a numerical failure or a sign of local instability rather than a confirmed global stability failure. Overall, this study highlights the importance of three-dimensional soil–structure interaction modelling for evaluating top-down excavation behavior in soft clay.