A numerical study on the deformation behaviour of geotextile encased stone column

Construction of embankments over soft soils is considered to be risky due to its inadequate load carrying capacity and high factor of compressibility. Majority being close to a sea or between rivers, large part of world is covered with soft clayey grounds, yet excessive need for new areas for urbanisation enforces the improvement of these weak grounds. Providing the rapid construction, consolidation acceleration, total and differential settlement reduction and adjacent facility protection advantages; stone column supported embankments become one step forward among variety of available techniques. Stone column is a cost-effective method for improving especially the weak ground under highways, railways and urban infrastructure. The stone column ensures its bearing capacity by means of the passive earth pressure resistance against the lateral deformation provided by the surrounding soil thus its performance depends on the shear strength of the soft clay soil. The encasement of stone column with a proper type of geosynthetic material is a widely used method to provide the required lateral confinement and to avoid dispersion of granular material into the soft clay. Along with improving the bearing capacity and reducing the settlement and bulging, geosynthetic encasement preserves stone columns easy drainage ability. Despite being widely investigated by many precious researchers with numerous valuable laboratory and in-situ experiments and numerical studies, there are still additional efforts needed to determine the performance, to fully understand the deformation behaviour and to predict long term serviceability of geosynthetic encased stone column. This study presents the results of finite element analyses of a hypothetical geotextile encased column supported embankment on a soft soil deposit which is improved by a geogrid reinforced sand mat on top. Numerical results of 2D analyses were validated by using field and experimental data of former studies at first, afterward parametric studies were carried out on two-dimensions finite elements model considering the effect of the soft soil thickness, the geosynthetic encasement length and stiffness, basal reinforcement (sand mat) thickness and geosynthetic reinforcement stiffness. Also, a group of floating stone columns in soft ground were modelled in two-dimensions and differential settlement behaviour was determined. By the parametric studies performed in the study; the optimum sand mat layer thickness, the geosynthetic stiffness, the optimum encasement length and the geosynthetic stiffness will be advised to be used for the preliminary design. This will contribute to the development of economic design methods for end-bearing and floating types of vertically encased stone columns and geosynthetic reinforced sand mat layers. Thus, the usage of stone columns on soft clay soils which is an easy and economical ground improvement method because of providing the design flexibility through the soil material in the field, can become widespread.