Abstract: This paper presents a numerical comparison of the vertical pull-out capacity of square and circular anchors in purely cohesive soils (i.e. clays in undrained conditions). For simplicity, ultrathin, infinitely rigid anchors are considered and to isolate the effect of anchor shape, comparisons are made between anchors of equal area and embedment depth. Finite Element Limit Analyses (FELA) are used to compute upper and lower bound values of the break-out factor over the full range of embedment ratios, and the associated failure mechanisms are identified. The results show for the first time (to the best of the authors' knowledge) that square anchors exhibit slightly higher efficiency at shallow embedment ratios due to their larger perimeter, while at greater depths, circular anchors become more efficient as a result of the different failure mechanisms involved. The study also investigates the influence of anchor inclination and shows that inclined anchors have a higher pull-out capacity in vented conditions due to elongated failure mechanisms. Under attached conditions, the deep failure mechanism is obtained in most cases with the corresponding constant break-out factor. In addition, the paper analyses the influence of anchor spacing in anchor groups, identifying optimal spacing to avoid capacity reduction due to interaction effects. For shallow depths, a spacing of about two times the anchor width is sufficient, while deeper installations require larger spacings due to the extended failure zone. Once the deep ailure mechanism is reached, spacing requirements decrease again, less than two times the anchor width. Overall, the presented numerical simulations offer insights for the design of plate anchors in cohesive soils, contributing to the advancement of offshore foundation technologies.
