Experimental Analysis of Embankment on Ordinary and Encased Stone Columns

Abstract

This work investigated the behavior of embankment models resting on soft soil reinforced with ordinary and encased stone columns (ESCs). Model tests were performed with different spacing distances between stone columns and two length-to-diameter ratios (L/d) of the stone columns, in addition to different embankment heights. A total of 39 model tests were performed on soil with an undrained shear strength of ≈10 kPa. The system consisted of a stone column–supported embankment at different spacing-to-diameter ratios (s/d) of stone columns. Earth pressure cells were used to measure directly the vertical stress on the column for all models, and another cell was placed at the base of the embankment between two columns to measure directly the vertical stress in reinforced soft soil. For embankment models constructed on soft clay reinforced with ESCs, it was found that whether a column was floating or end bearing (resting on a rigid stratum), encasement of the column by a geogrid was most effective in improving the bearing ratio of reinforced soil by approximately 1.29, 1.39, and 1.63 times and 1.4, 1.57, and 1.83 times that of untreated soil, reducing the settlement by approximately 0.71, 0.67, and 0.62 times and 0.63, 0.6, and 0.45 times that of untreated soil for 200-, 250-, and 300-mm embankment heights with L/d = 5 and 8, respectively, and spacing s=2.5d. The bearing improvement ratio (bearing capacity of treated-to-untreated soil) increased with decreasing spacing of stone columns for a given embankment. A higher improvement ratio was achieved for the models reinforced with stone columns at s=2.5d at any embankment height.