Influence of geotextile encasement on the behaviour of stone columns: Laboratory study

This paper presents a study of the influence of the geotextile encasement on the behaviour of soft soils improved with fully penetrating encased columns. This influence is analysed by means of measuring soil-column stress distribution, pore pressures and soil deformation during the consolidation process. For this purpose, a horizontal slice of a representative “unit cell” has been analysed by means of small-scale laboratory tests. The tests were carried out in a large instrumented Rowe-Barden oedometric cell. Results showed that the vertical stress supported by encased columns is about 1.7 times that sustained by the non-encased ones. The stress concentration factor for encased columns is between 11 and 25, which is clearly higher than that obtained in tests with non-encased columns, which are between 3 and 6. Finally, the improvement in relation to settlements is presented by the ratio of settlement in soils reinforced with ordinary or encased columns and the settlement of non-treated soft soil. This settlement reduction factor is around 0.6 when the soil is treated with encased columns and 0.8 for soil with non-encased columns.