Research in unsaturated soil mechanics has considerably developed in the past decades, through the simultaneous development of experimental investigations and theoretical analyses. An attempt has been done to investigate the influence of the negative pore water pressure (matric suction) on the behavior of single pile and pile group with five configurations, and the amount of increase in the bearing capacity due to the influence of this suction using special device for this purpose. Further, the stress distribution inside the stress bulb for both saturated and unsaturated soil conditions using special instruments inserted at o.25L below the pile tip is also investigated. The experimental results of bearing capacity and load transfer are compared with different theoretical approaches are obtained. In addition, a numerical simulation to the pile-soil problem is carried out by the finite element method. The computer program Geo Studio is adopted in the analysis.