Groundwater-Controlled Settlement of Raft Foundations on Marine Clay

This study investigates the vertical settlement behavior of marine clay beneath a raft foundation under varying groundwater levels (GWL). Laboratory testing conducted in accordance with Vietnamese Standards (TCVN) and numerical simulations using the Finite Element Method implemented in PLAXIS 3D were performed to evaluate ground deformation characteristics. Experimental results show that the maximum settlement reached 20.77 cm at a GWL depth of 22.3 m under a loading of 800 kN/m². Within the GWL range of 15.3–19.5 m, the total deformation modulus ( K _deformation ) , cohesion ( K _cohesion ) , and Young’s modulus ( K _Yeelastic ) were 44.38 kN/m², 40.2 kN/m², and 200.78 × 10² kN/m², respectively. The shear resistance ( K _{shear resistance} ) attained 124.1 kN/m² under 200 kN/m² loading, corresponding to a vertical displacement ( K _dis ) of 0.052 cm at 14.8 m depth. In contrast, numerical simulations predicted a higher maximum settlement of 150.7 cm, with simulated cohesion ( C _simu ) and Young’s modulus ( E _simu ) of 32.2 kN/m² and 141.2 × 10² kN/m², respectively. Pore water pressures reached 227 kN/m² at 7.3 m depth, associated with a settlement ( K _simudis ) of 25.180 cm. The results demonstrate the significant influence of groundwater level fluctuations on settlement behavior and provide a reliable reference for foundation design on marine clay in coastal regions.