Behavior of Swelling Soil Treated by Grid Geocell Columns under a Tank Footing

Abstract

Fuel tanks usually induce large settlements due to heavy loading which requires treatment for the underlying soils. In this paper, a method of treating the swelling of expansive soil is presented. The method is simply based on the embedment of a geogrid (or a geomesh) in the soil. The geogrid is extended continuously inside the volume of soil where the swell is required to be controlled and orientated in the direction of swell. Soils with different swelling potentials were employed; bentonite-based Na and kaolinite mixed with bentonite. To investigate the swell, swell- partial shrinkage and other phenomena for untreated soils in comparison with their counterparts of treated soils, laboratory model tests were carried out in 800 200 mm box container and 600 mm in height. Swelling and cyclic wetting along with drying tests were carried out on each sample with pore water pressure measurement. Swelling test in the model reveals promising results of the proposed treatment technique. The improvement factors, range between 30% to 60 % depending on the geogrid stiffness, soil plasticity, fill martial (sand or clay) and dry density of sand fill. The geocell has a significant effect on the experimental results. The reduction in swell increases with increasing the geogrid stiffness and when using sand as a fill material, the reduction is apparently due to a strong interference bond which restricts the relative movement between the clay and the grid. The use of geocell filled with the same expansive soil causes a decrease by about 19% and 42 % in the final swelling of soils, whereas filling the cell with sand causes about 35 % and 64 % reduction for the soils, respectively. The treatment method shows the activity of geocell fill material in reducing the matric suction (pore water pressure). When sand is used, a new channel is created for the dissipation of pore water pressure.