Construction over highly compressible soils can create excessive settlement and bearing capacity problems. To overcome these difficulties, deep foundation elements such as driven piles or drilled shafts have been traditionally used to transfer the surcharge loads exerted by the superstructures to a more competent layer at greater depths. These methods are relatively expensive when constructed over large areas and may also cause unwanted delay during construction. In recent years, rammed aggregate piers (RAPs) as a cost beneficial alternative to deep foundations, widely used in geotechnical engineering design and construction. Predicting the effects of piers in settlement control and capacity enhancement of foundation supported by Rammed Aggregate Piers is an important aspect of RAPs-supported foundation design. To quantify these effects, a three-dimensional numerical modeling of rammed aggregate piers using a finite-element approach by considering installation effects was developed and a parametric study performed in different conditions of geometry and matrix soil properties. the thesis presents the results of this parametric study and provides new insights into group behavior of piers when they are subjected to static and dynamic loads. Results of this study focused on the load-settlement behavior of RAPs-supported foundations and group effects.