Influence Zone for End Bearing of Piles in Sand

An attempt is made to establish an analytically based estimate of the influence zone surrounding the tip of a loaded pile in sand. In the framework of the cavity expansion theory and a confined local failure mechanism, explicit expressions are derived in which the sizes of the upward and downward influence zones are properly linked with the angle of shearing resistance, the stiffness, the volumetric strain, and the mean effective stress of the sand at the pile tip. Based on a series of parametric analyses, the mean range of the influence zone is suggested. For piles in clean sand, the influence zone above the pile tip is between 1.5 and 2.5D and the zone below the tip ranges from 3.5 to 5.5D, where D is pile diameter. For piles in more compressible silty sand, the influence zone extends between 0.5 and 1.5D above the pile tip and between 1.5 and 3D below the tip. Because of its analytical nature, the present study may provide a meaningful insight into the current empirical interpretations.