This research is conducted to study the effect different grain size distribution of cohesionless soils (i.e. fine, medium and coarse sand) and pipe pile diameters on the degree of soil plugging and plug length ratio under different saturation conditions (i.e. fully and partially saturated). Karbala sand, were used as a natural soil in the present study, it is poorly graded clean sand of rounded particles. The sandy soil is sieved to obtain a fine, medium and coarse graded according to (ASTM D 422-02)[3]. The experimental model tests conducted on four open-ended steel pipe pile models with diameters of (25, 30, 35 and 41mm). embedded within different grain size distribution of sand prepared under fully and partially saturated conditions with predermined relative density of 65%. The unsaturated states were achieved by lowering of water table according to predetermined matric suction values of soils. The relationship between matric suction and depth of ground water table was measured in suction profile set by using three Tensiometers (IRROMETER). The soil, water characteristic curve (SWCC) was estimated by applying fitting methods through the program (Soil Vision). The results shows that, the plug length ratio (PLR) (The proportion of a soil plug length to the pile penetration depth) which was measured for different pile diameters, and different grain size distribution in unsaturated conditions, for the same pipe pile diameter increase with increasing the matric suction values and the length of soil column inside the pipe pile increase gradually with the increasing of a piles diameter.