Large-Scale Experimental Study on Collapsible Soil Improvement Using Encased Stone Columns

Document Type : Original Article


Department of Civil Engineering, Shahid Bahonar University of Kerman, Kerman, Iran


The aim of this study was to improve the characteristics of natural collapsible soils using the geogrid-encased stone column technique. For this purpose, 20 large-scale specimens of stone columns were prepared using rigid metal cylinders with a diameter of 308 mm and a height of 97 to 154 mm according to the unit cell theory. The aspect ratio was 10% to 25%. For the occurrence of bulging failure, the height of the stone columns was considered six times the diameter. The stone columns were encased with geogrids of varying stiffness from 80 to 200 kN/m. The soil around the stone column inside the unit cell was compacted to similar site conditions. Loading was applied similar to the test, which determines the soil collapsibility potential while the specimens were being inundated from the bottom of the metal cylinder by a water feeding system. During loading, the vertical displacements of the stone columns were measured at two locations on the loading plate. The results showed that the columns settlement due to inundation diminished by increasing the stiffness of the encased stone columns and aspect ratio. The optimum aspect ratio was approximately 15%. Encasement of the stone columns increased the lateral pressure in the collapsible soil and prevented the collapse of the stone column. The settlement values of stone columns were compared with a settlement prediction model and showed a good agreement. The data obtained in this study can be used as a practical method to improve natural collapsible soils during inundation.


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