Simulation of the Numerical Behavior of Stone and Geosynthetic Encapsulated Sand Columns in Tuzla area

ABSTRACT: One of the major challenges among engineers is to construct various types of structures over weak soils. Among various technologies implemented by engineers, stone or sand columns are the most beneficial methods for modification of weak soils, such as alluvial soils. These methods mitigate poor deposits, modifying their properties by the use of materials such as stone or sand. The target of present study was to determine the influence of stone or sand columns in alluvial deposits of Tuzla. For this purpose, numerical simulation was carried out to model the behavior of settlement, excess pore water pressures, stresses around columns, bulging, hoop tension force and consolidation time. The Plaxis finite element software was used to evaluate the effect of columns in undrained condition. Mohr-Coulomb model was selected for all materials. In Plaxis the axisymmetric analysis for unit cell and plain strain analysis for full-scale analysis were used. In this thesis the settlement, excess pore water pressures, stress, and consolidation time were analyzed to determine the behavior of stone column under an embankment construction in unit cell and full-scale conditions. In addition, the bulging and hoop tension force around encapsulated sand column with geotextile was analyzed. The results of this study indicate that, stone column has a remarkable influence on decreasing settlements and accelerate the consolidation time. Larger the column diameter, higher is the bearing capacity and lower is the settlement. The maximum settlement occurs at ground level and reduces by increasing depth and increasing column diameter. By using stone column due to larger stress confining around stone column, the amount of vertical settlements increased in stone column and rapidly decreased by increasing distance from column, and afterwards remained constant. The maximum bulging occurred at 1.06D of sand columns. By increasing, the diameter of columns bulging increased. Using geotextile with higher stiffness, amount of bulging reduced, also value of the hoop tension force increased. Therefore, higher stiffness has lower settlement compared to conventional sand column. Lateral settlements increased initially and then reduced with increasing depth, and distance from the embankment. Keywords: Alluvial soil, embankment fill, Plaxis, stone column, encapsulated sand column, hoop tension. ……………………………………………………………………………………………………………………………………………………………………………………………………………………