EXPERIMENTAL STUDY ON NATURAL BAMBOO GEOGRID ENCASED STONE COLUMN

As bamboo is easily available and cheaper in India with respect to polyester geogrid and also environment friendly, an attempt has been made to use natural bamboo material to improve the soft ground conditions. Stone column has been adopted as ground improvement technique and bamboo encasements are prepared to encapsulate the stone columns. Narrow bamboo sticks of 10 mm width with proper finishing are collected to prepare the encasement. Laboratory model tests have been performed on end bearing stone columns installed in soft marine clay. Partial and full length natural bamboo geogrid encasements are prepared to encapsulate the stone columns. Size of the stones used to model the stone columns is ranging from 2 mm to 10 mm. Partial bamboo encasements of 2D and 3.5D length are chosen for the experiments where ‘D’ is the diameter of column. Experimental results indicate improved load carrying capacity of stone column with increase in the length of bamboo encasement. Full length encasement prepared with polyester geogrid is also used to investigate the effectiveness of the natural bamboo geogrid encasement. Higher load carrying capacity is observed by using stiffer bamboo geogrid encasement at the same applied pressure. It is evident from the laboratory investigation that bamboo encasement can be an effective alternative at a cheaper cost than the polyester geogrid encasement. A finite element analysis has been performed using software ‘PLAXIS 2D Professional’ (2011) to find out the radial deformation of stone columns without and with full length encasement. Tensile strengths of bamboo geogrid as well as polyester geogrid are used to model the encasements in the finite element analysis. Reduced radial deformation is observed with increased stiffness of the encasement. An analytical study has also been performed with some simplified assumptions. It is observed from the analytical study that with increasing applied pressure, lesser hoop strain is developed in the full length bamboo geogrid encasement compared to the polyester geogrid encasement.