The stone column encasement is a widespread ground improvement technique that effectively improves the engineering characteristics of weak and compressible soils with excessive settlement problems under vertical loadings. Despite the extensive use of stone columns, the settlement response of sandy soils reinforced with various geosynthetic encasement configurations under cyclic loading conditions remains unexplored. This study aimed to understand the settlement response of sandy soils reinforced with dual-layer geosynthetic-encased stone columns (DLGESCs), single-layer geosynthetic-encased stone columns (SLGESCs), and ordinary stone columns (OSCs) under cyclic loading conditions. The effects of cyclic loading amplitude, frequency, and geosynthetic encasement on settlement behavior were investigated using PLAXIS-3D (version 21) software with the hardening soil small constitutive model, and geosynthetic encasements with variable axial stiffness and tensile strength were studied. The study results indicated that higher cyclic loading amplitudes and frequencies increase the settlement of the stone column. DLGESC outperformed SLGESC with a 5.8%-11.2% settlement reduction, while SLGESC reduced settlement by 40.9%-47.8% compared to OSC. Geosynthetic GT3 (800 kN/m axial stiffness, 70 kN/m tensile strength) decreased settlement by 7.6%-13.6% compared to GT1. This research emphasizes ground improvement techniques and demonstrates the way DLGESC reduces settlement and improves structure stability on stone column-reinforced sandy soils. This study can help design resilient and stable foundations for pavements, railroad tracks, and offshore structures under cyclic vertical loading characteristics and suitable encasement configurations.

This paper presents the results of large shaking table tests to investigate the improvement effects of using ordinary stone columns (OSCs), geosynthetic-encased stone columns (GESCs), and surrounded stone columns with filtering material (FSCs) on saturated sand. The internal dimensions of rigid box were 2.35 m and 0.9 m in plan and was filled with 1.1 m Firuzkuh sand using the water pluviation method. The diameters of stone columns (SCs) were 120 mm and 170 mm and the SCs spacing was 300 mm. The embedded lengths of SCs were 1100 mm. The results indicate that, although the increase in excess pore water pressure is not restrained by using OSCs, the use of both GESCs and FSCs are more effective to mitigate liquefaction potential. This is because of the effectiveness of the geotextile and sand filter on preventing the clogging of SCs and allowing permanent drainage of SCs during shaking. It was found that in the cases of unimproved sandy ground and improved sand by OSCs at 0.05 g loading horizontal acceleration, sand became totally liquefied, while in the cases of improved sand by GESCs or FSCs, under approximately 0.2 g acceleration, the soil close to the SCs was not liquefied.