Shear Strength of Geosynthetic-Encased Stone Columns in Unsaturated Soils

Stone columns are often subjected to shear deformations due to in-situ soil movement that ultimately leads to the shear failure of stone columns. This phenomenon is observed in both saturated and unsaturated soil conditions. For this reason, the objective of this study is to evaluate the behaviour of stone columns with and without geosynthetic encasement, subjected to shear loading conditions extending the mechanics of saturated and unsaturated soils. A series of large direct shear tests were conducted to account for the influence of matric suction on the shear strength of the soil reinforced with conventional and geosynthetic encased stone columns, using the soil–water characteristics curve as a tool. The study reveals that both matric suction and net normal stress play a pivotal role in the hardening–softening behaviour of the stone columns, contributing to their mechanical response and overall stability under shear forces. The shear strength of soil reinforced with stone columns, regardless of geosynthetic encasement, exhibited a direct relationship with matric suction until the primary transition zone of the soil–water characteristics curve. However, a further increase in matric suction reduced shear strength due to a decreased water-menisci area in contact. Geosynthetic encased stone columns exhibited distinctive behaviour compared to conventional stone columns, demonstrating a bending-type deformation without rupturing the encasement material. The interplay between matric suction, net normal stress, and mechanical behaviour highlights the importance of considering these factors for optimized stability and performance of geosynthetic encased stone columns.