Experimental study on the performance of soft soil reinforced with geotextile-encased sand columns

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Abstract Soft clay soils, prevalent in coastal and alluvial regions worldwide, exhibit low shear strength, high compressibility, and poor drainage, posing major challenges for construction. Geotextile-encased sand columns (GESC) offer an effective ground improvement technique by enhancing load-carrying capacity, stiffness, and drainage. A series of small-scale undrained triaxial tests was performed to examine the mechanical response of both ordinary sand columns (OSC) and GESCs, with a focus on the effects of column diameter, area replacement ratio, and cell pressure. Each test comprised saturation, isotropic consolidation under cell pressures of 50, 100, and 150 kPa, and subsequent undrained axial shearing at a constant displacement rate of 0.02 mm/min. Results show that the GESC increased the composite friction angle from 27° for unimproved soil to 30° at a 25% area replacement ratio. The peak stress ratio relative to unimproved soil was consistently higher for GESC (1.69) than for OSC (1.57) at the same area ratio, due to the additional confining stress provided by the encasement, showing about 20% greater settlement reduction compared to the OSC. An increase in the area replacement ratio from 6 to 25% resulted in an approximately 62.5% reduction in the average additional confining stress. While OSC primarily failed by bulging, GESC promoted a more favorable shear failure and reduced bulging deformation. Consolidation times were slightly longer for GESC (about 32% longer at 25% area ratio) due to clogging, but still achieved 430% faster consolidation than unimproved soil. Overall, GESC provide enhanced confinement and stability, making an effective solution for soft clay foundations.

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