A comparative study of some major national design approaches and construction practices in the treatment of soils using stone columns with or without encasement

Abstract

This thesis investigates and compares the design principles, bearing capacity calculations, settlement prediction methods, and special construction practices for stone columns, with and without geosynthetic encasement. The study reviews major national design standards, including Indian Code, the US Code, French Code, German Code, and Murugesan & Rajagopal’s laboratory research, to identify how different approaches design stone columns in soft ground. A detailed comparison of bearing capacity and settlement estimation shows that uncased stone columns are effective if the surrounding soil provides sufficient radial confinement. However, the results highlight that in very soft or sensitive soils, the lateral confinement is insufficient to resist the bulging under vertical load, leading to lower capacity and higher settlement. In such case, encased stone columns can provide an additional source of radial confinement through the hoop tension of the casing, significantly improving stress concentration ratios and reducing settlement. This finding is supported by Murugesan & Rajagopal’s model tests and confirmed through comparative checks using German Code’s stress approach. An assumed marine mud condition based on Hong Kong examples is used to demonstrate the differences between the design approaches. The study also compares practical stone column construction aspects, in terms of installation method, loading types, stone aggregate properties, blanket layers, and field control. Overall, the findings reveal that the effectiveness of uncased and encased stone columns depends on the design assumptions, site conditions, and construction quality.