Drained triaxial response of clay reinforced with sand columns

In ground-improvement applications involving stone columns in soft clays, the columns act as drains that facilitate partial drainage during practical load applications. Partial drainage could improve the short-term strength of the clay/column composite. The objective of this work was to bracket the range of loading conditions by investigating the fully drained response of clay/column composites through consolidated drained triaxial tests. The area replacement ratio, the column penetration ratio and the presence of geotextile encasement were varied in the testing programme. A maximum improvement of 69% was observed in the deviatoric stress for area replacement ratios of 31·7%. A comparison between identical drained and undrained tests indicated that the deviatoric stresses were higher in drained tests with the drained response representing an upper bound for the strength of the reinforced clay specimens. When the improvements observed in triaxial tests were compared with improvements witnessed in full-scale footing tests, the triaxial test results seemed to over predict the per cent improvement observed in the field bearing capacity.