Shear behavior of geosynthetic encased columns embedded in soft soils

In this study, the static and cyclic shear behavior of ordinary and geosynthetic encased columns embedded in soft soils are investigated. In the former researches, it was seen that the shear behavior of geosynthetic encased columns were not studied sufficiently. In these few studies, the scale ratio is not considered, and the other field conditions are not represented in the models. Although the shear and bending failure mechanism are also common, the lack of research might be explained by the lack of sufficient and required experimental setups and models and by the newly recognition of these failure modes. Therefore this study was focused on the shear behavior of the ordinary and geosynthetic encased columns and the Unit Cell Shear Device was used. This is the fi rst time that UCSD is used to investigate the shear behavior of GECs and OSCs in clay. The Unit Cell Shear Device can shear unit cells prepared with stone columns that are slender and have relatively high model to prototype diameter ratios (approximately 1:3.5). 5 types of unit cells were used in this study, namely, benchmark unit cell, unit cell with ordinary stone column and the unit cells with encasements made by 3 different types of geotextiles. The surrounding soil in these unit cells were prepared in 3 different consolidation loads, namely 15 kPa, 25 kPa and 35 kPa. All these unit cells were prepared as 2 sets and they were tested under static and cyclic loading. During the experiments, horizontal displacement and shear loading readings were taken. For the experiments with geosynthetic encased columns, strain readings in 3 levels were, also, taken. The equivalent friction angles at different horizontal displacements for both static and cyclic shearing were calculated in order to evaluate the soil improvement capacity for geosynthetic encased columns using geotextiles with different stiffnesses.