Investigation of behavior of stone columns in clayey sand soils with laboratory model tests

Various improvement methods have been developed for structures constructed on soft soils to solve bearing capacity, excessive deformation and other stability problems such as lateral spreading and local failure. In this study, a mixture of clays and sands at a high water content are placed in cylindrical tanks that have a diameter of 1.1 meters and a height of 1.35 meters. Then this soft soil is consolidated at different pressures. Standard stone columns are constructed and plate loading tests are conducted on the consolidated soils utilizing the loading frame that has been previously used for thesis work at the YTÜ Civil Engineering Department Geotechnical Engineering Division. The results of loading tests and finite element method obtained by Plaxis 2D were evaluated. Within this study, gages to measure soil and pore-water pressures are placed at various locations throughout the sandy clay soil, so that more precise analytical and numerical evaluations of the measurements can be made. Thereby, a comparison of the changes in soil and pore pressures and of the load-displacement behavior is made between an unimproved soft soil and one that is improved with a stone column during the construction and axial loading stages. The improvement ratio, i.e., the increase in the bearing capacity of the cell which consists of the stone column and its nearby zone, may be determined with the aid of these measurements. Block samples are taken from the sandy clay soil before and after the construction of stone columns and soil shear strength parameters (c, ϕ) and modulus of elasticity is obtained through triaxial tests (CD, CU), unconfined compression tests. Furthermore, vane shear testing is conducted to determine the improvement around the stone column. Key Words: Stone Column, Laboratory Model Tests, İmprovement Ratio, Pore Water Pressure, Stress, Numerical Analysis