Effect of Construction Method on the Performance of Ordinary and Geotextile-Encased Stone Columns

The present study aims to investigate experimentally the effect of construction method on the performance of stone columns. Floating-type uncased and geotextile-encased 6 and 8 cm diameter stone columns were constructed by replacement and displacement method. It is shown that bearing capacity is 20-30% higher in stone columns constructed using displacement method with respect to replacement method, and effect of construction method on the bearing capacity is more pronounced in stone columns with higher area replacement ratio. In 8-cm uncased stone columns with an area ratio of 16%, columns constructed with displacement method show 14% increase in bearing capacity with respect to those constructed using replacement method. In addition, effectiveness of the construction method in increasing bearing capacity is decreased, when geotextile-encased stone columns are used. The performance of stone columns is also investigated by varying the load improvement ratio (LIR), and stress concentration ratio (n). It is shown that LIR and n are both affected by area replacement ratio, and length-to-depth ratio. Both LIR and n increase with settlement and approach a constant value when settlement ratio becomes 5% or higher. Finally, a design curve is developed to evaluate stiffness and bearing capacity of stone columns. A design procedure, in the form of a flowchart, was suggested to obtain bearing capacity and stiffness of stone columns.