Multiscale Modeling of Anchor Pullout in Sand

Pullout of plate anchors from granular sands is investigated using a novel computational multiscale approach. We employ the material point method (MPM) to solve a large deformation boundary value problem and adopt the discrete element method (DEM) to derive the history-dependent material responses required for each material point of the MPM domain. The continuum-discrete hierarchical coupling between MPM and DEM not only helps to bypass the assumption of complicated phenomenological constitutive models for sand, but also facilitates the handling of large displacement movement of the anchor and its ensuing complicated interactions with surrounding soil. This multiscale method is used to simulate the pullout of both horizontally and vertically placed plate anchors in sand by a large displacement, and to examine the roles of key factors, including the relative density of sand and the embedment depth, on the bearing capacity and pullout behavior. For a horizontally placed plate anchor, a truncated cone shape of soil body is mobilized upward at shallow embedment depth, whereas at greater depths, the surrounding soil may flow from the top to the bottom of the anchor, forming an interesting circulating circular shape. For a vertically placed plate anchor, the failure pattern of soil evolves gradually from a general shear failure mode to a local rotational failure mode when the embedment depth is increased. The study also provides cross-scale insight for the macroscopic observation on anchor pullout and comparisons with past studies.