Influence of stone column length on consolidation performance of floating stone column in soft clay

Construction on weak or soft soils often requires ground improvement to ensure stability. Stone columns are effective in enhancing load-bearing capacity, reducing settlement, and accelerating consolidation. When the soft layer is too thick for full penetration, floating stone columns partially embedded columns that do not reach a firm stratum are used. However, predicting their consolidation behavior, particularly in double layered soils, remains challenging as stone column improved layer are having higher stiffness and faster consolidation rate compared to the below untreated layer. This study investigates the consolidation performance of floating stone columns, focusing on excess pore pressure dissipation and stress concentration ratio. A series of physical model tests were conducted on single floating stone columns installed in kaolin clay using a unit cell tank under an applied load of 11 kPa. Column lengths of 0 mm (unreinforced clay), 80 mm, 160 mm, 240 mm, 320 mm, and 400 mm (end-bearing) were examined with area replacement ratios (Ar) of 15% and 33%. Results were validated using PLAXIS 3D finite element analysis. The findings show settlement reduction up to 68.06% and faster pore pressure dissipation with increasing column length. Settlement differences between laboratory and numerical analysis ranged from 3.64% to –9.47% for Ar = 15% and 9.14% to –7.23% for Ar = 33%. Stress concentration ratios increased with column length and Ar, ranging from 2.01 to 4.51 (laboratory) and 1.68 to 4.59 (numerical). Besides, the lab and numerical result were verified with existing analytical solutions where good agreement were obtained. Finally, a new equation is proposed to predict the settlement improvement factor for floating stone columns.