Behavior of Geosynthetic-encased Granular Column in Silty Sand Soil by Direct Shear Test

This paper investigates the reaction of geo-synthetic encased granular columns (EGCs) in loose silty sands under lateral loading. 48 large scale direct shear tests are performed on granular columns to study the effect of Area Replacement Ratio (Arr), encasement, normal stress, group action and granular column grading. The results showed that in the case of ordinary granular columns (GCs) the residual and peak strength increased up to 80% for 10 kPa normal stresses and up to 35% for 30 kPa normal stresses, respectively. Also the residual strength increased by increasing area replacement ratio. In the case of geo-synthetic encased granular columns (EGCs) the residual strength increased from 15% to 40% compared with GCs. In the case of a group of encased granular columns at 60 kPa normal stress, the residual strength increased from 23% to 40% compared with a group of not-encased granular columns. But In the case of the single encased granular column at 60kPa normal stress, the residual strength increased from 15% to 25% compared with single not-encased granular columns. By increasing the size of grains of EGCs at 60 kPa, the normalized residual strength increased up to 36% compared with not-encased granular column. The results of tests showed that the effect of granular columns in lateral resistance decreased by increasing fine content.