Expansive clays often cause significant disruptions to the lightweight constructions built over them. As such, this paper attempts to predict and describe the movements of expansive clays when seasonal hydration and vertical loadings change. However, three-dimensional coupled hydro-mechanical finite element analysis (3DFEA) was conducted using PLAXIS3D to predict the time-dependent behaviour of a heave marly clay layer underlain by a natural substratum of gravelly sand supporting a symmetrical small five-storey building (SBSC). A stiffened raft with basement walls, anchored at \(- 3.0{\text{ m}}\) excavation depth, was adopted as foundation system. Moreover, the 3DFEA was performed, considering simultaneously phreatic level and vertical loading changes. However, a threshold load of \(60 {\text{kN}}/{\text{m}}^{2}\) which corresponds to the unloaded stress of removed excavation soil is adopted to assess swell behaviour, considering three vertical loadings below it: \(18, 30\) and \(40 {\text{kN}}/{\text{m}}^{2}\) and compressive one for three other ones above it: \(70, 80\) and \(90 {\text{kN}}/{\text{m}}^{2}\) , respectively. Indeed, two phreatic levels \(\left( {{\text{D}}_{{\text{w}}} } \right)\) of \(- 3.75\) and \(- 0.75{\text{ m}}\) are considered and systematically combined with these vertical loadings \(\left( {{\text{Q}}_{{\text{v}}} } \right)\) . According to main analysis results, although a swelling state prevails during the construction period, regardless of these two combined factors, the unsaturated case exhibits significant swell compared to the high consolidation settlement observed in the saturated one. Nevertheless, secondary compression in saturated case continues to develop slowly but with increasing amplitude showing that, the creep phenomenon seems not obvious. This study concluded that a stiffened raft with basement walls appear as a suitable alternative for symmetrical SBSC by undertaking specific improvement treatments.
