Abstract: A three-dimensional numerical method is used to delicately simulate the installation and in-situ loading tests on a single rammed aggregate pier(RAP) with the initial diameter of 0.76 m and initial length of 5.05 m.An unrammed aggregate pier(UAP) with the same dimensions is also simulated using the numerical method for the purpose of comparison.The computed and measured settlements at the top and bottom of the RAP are in good agreement.The ratio of the UAP to RAP top settlements is 1.8 to 10.7 whereas their bottom settlements are quite small.The bulging along the UAP shaft is much greater than that along the RAP shaft at the same loading.The magnitude of axial forces along the RAP shaft decreases significantly with depth,while for the UAP,the bulging along the shaft becomes greater as the top loading increases to a certain level.The bulging increases shaft friction forces.As a result,the magnitude of axial forces along the shaft decreases significantly with the depth.