G MS THESIS_final version_Maxim Prokudin.pdf - Digital Repository ...

35Case 5 – Bachus and Barksdale, 1984 – Vertical and Lateral Behavior of Model StoneColumns (Georgia Institute of Technology, Georgia)The investigation was performed on model sand columns at the Georgia Institute ofTechnology. Two different size columns were tested at 29 mm and 53 mm diameters.Columns were constructed using sand material and placed in test chamber 108 mm indiameter, 305 mm in height, and with wall thickness of 16 mm. Uniformly graded mediumsand was compacted in even size lifts in a pre-augered cavity using an air actuated hand heldvibratory compactor.Soft kaolin clay was used as the matrix soil where the columns were placed and tested. Thesoil was consolidated within the chamber to achieve 45 to 60 kPa undrained shear strength.The kaolin clay was described as uniform silty clay composed of 35 percent of clay andhaving liquid limit and plasticity index of 42 and 15 percent, respectfully. Once theconstruction was completed, single and groups of columns were tested for lateral responseand load-settlement evaluation. Radiographic method was used to evaluate the lateraldisplacement of the column within the matrix soil. Lead markers were also used toinvestigate the shape of the columns after the columns were tested.Area replacement ratio, defined as ratio of the diameter of the stone column to the diameterof the unit cell, was 0.4. It was found that the groups of stone columns had a tendency tosupport a load 40 percent greater than the load imposed on unreinforced soil of the sameloading area. Moreover, a significant effect of time rate of loading was observed, where theload carrying capacity of a group of columns was 60 to 70 percent greater when the loadingwas performed in a slower fashion and slow dissipation of pore water pressure was allowed.The area replacement ratio was found to be an important parameter when performing lateralload tests on the columns. The shear strength of the unreinforced kaolin clay soil was foundto be higher than when the soil was reinforced with columns at 0.14 area replacement ratio.