Encased Stone Columns for Soft Ground Improvement

The encased stone column technique is a sustainable, energy saving and geoenvironment friendly effective alternative approach to the conventional reinforced concrete pile foundations. Geosynthetic materials are generally suited as encasements owing to the excellent tensile properties enabling those to produce sufficient circumferential stress around the column and prevent the bulging failure in very soft soil having undrained shear strength below 12-15 kPa. Different types of geotextiles and geogrids of different tensile stiffness are used as the encasement material. Encased stone columns are easy to install as well as cost of the project gets enormously reduced. This study focuses on the influence of encasement stiffness and its varying lengths to the stone column behaviour through numerical modelling of a floating encased stone column installed in very soft soil of undrained shear strength 6 kPa. Results indicated enhanced capacity of the stone column with increase in encasement stiffness. Also with increase in encasement length, the column capacity increases. Providing a partial encasement length, four times the column diameter, improved capacity around 2.25 times that over only stone column was achieved at a settlement 12% of footing width. Providing an encasement of adequate length and stiffness, around three folds enhanced capacity was achieved compared to that of only stone column. Small scale model tests were also performed on encased stone column in laboratory and the same were modelled in the finite element software for validation purpose. The finite element results were found in good agreement with the experiment results.