Behavior of Geotextile-Encased Single Stone Column in Soft Soils

Stone columns have become a widely used method of increasing bearing capacity of soft soils. This study investigates floating stone columns with and without encasement in soft soils. Although the stone columns in single-layered soil have been studied extensively, stone columns constructed in a base of varying soil layers are not fully understood. In the present study, the behavior of both single-layered soft soil and layered soil consisting of loose sand overlaying the soft soil was investigated by using small-scale laboratory pilot tests. The bearing capacity of soft soil was improved in all cases of stone column application. The contribution of stone columns on the bearing capacity of soft soil was presented by the term bearing improvement ratio (BIR). With a non-encased stone column in single-layered soft soil, the BIR was about 3.3-fold and with geotextile encasement in the same soil, the improvement ratio increased to 3.4-fold. For a non-encased stone column in layered soils, the BIR was about 2.0-fold and with geotextile enhancement in the same soil, this improvement ratio increased to 4.0-fold. The inclusion of geotextiles resulted in improved bearing capacity by distributing the induced stresses over larger areas. The maximum bulging of non-encased stone column in single-layered soft soil was observed at the depth of 1.5 times the original diameter of the stone column from the top, whereas for encased stone column in single-layered soft soil, the maximum bulging was transferred to a depth of 3.0 times the original diameter of the stone column.