Investigation of behavior of rammed aggregate piers by constructing clayey sand soils with laboratory model tests

In recent years rammed aggregate piers (RAP) have been increasingly used for improvement of soft soils to increase the load bearing capacity and to reduce the settlements. This ground improvement technique have been successfully applied for the foundations of structures, such as oil storage tanks, embankments, raft foundations, etc., where large settlements are likely to take place. This thesis presents the results from a series of laboratory tests carried out on a rammed aggregate pier installed in different sandy clay beds formed in a large scale model test tank that has a diameter of 110 and 90 cm height. The installation the rammed aggregate pier within the model tanks was achieved through a large scale column installation machine constructed in the YTÜ Geotechnical Engineering laboratory. The soft clay beds were prepared in the large model test tanks by mixing 60% sand, 40% clay with a water content of 1.5 times the liquid limit of the clay. Instrumentation consisting of stress cells were installed at different depths of the clay bed. The slurry mixtures were allowed to consolidate one-dimensionally under different pressures by using air bag or dead weight on the surface to apply the pressures. Drainage was permitted at the top and bottom of the clay beds and the settlements in the clay beds were monitored using mechanical dial gauges. The consolidation of the clay beds continued for a period of maximum five months to minimum a month. After the completion of primary consolidation, 10 cm diameter rammed aggregate pier were installed at the center of the clay beds. Then the columns were subjected to vertical loading at the top through a loading plate displaced by the column installation machine. The load deformation behavior of the rammed aggregate pier, improved soil and unimprovement soil were investigated by evaluating the measurements obtained from the stress cells. In concIusion important result about the improvement ratio of rammed aggregate piers and working mechanism under axial load are obtained by conducting model experiments.