Effect of particle size distribution of cohesionless soils on the ultimate carrying capacity of open ended pipe piles under different saturation conditions

This research is performed to study the effect of grain size distribution of cohesionless soils (i.e., fine, medium, and coarse sand) on the ultimate carrying capacity of open-ended pipe pile models of different diameters under different saturation conditions (i.e., fully and partially saturated). Poorly graded clean sand of rounded particles was used as natural soil in the present study. The soil is sieved on standard sieves to obtain fine-, medium-, and coarse-graded soil according to (ASTM D 422-02). Experimental model tests were performed on four open-ended steel pipe piles models with diameters of (25, 30, 35, and 40mm) embedded within different grain size distribution of sand prepared under fully and partially saturated conditions with specified relative density of 65%. The unsaturated states was achieved by lowering of water table according to matric suction values of soil. The relationship between matric suction and depth of ground water table was measured in suction profile set by using three Tensiometers. The soil water characteristic curve (SWCC) was estimated by applying fitting methods through the program (SoilVision). The results show that the ultimate load carrying capacity of pipe pile under unsaturated conditions is higher than those of saturated condition and increases with increasing of matric suction values. On the other hand, the fine sand shows an increase in ultimate load carrying capacity more than the other grain size distributions under unsaturated conditions for all different types of pipe pile diameters. However, the coarse sand gives a lower resistance at different saturation conditions.