Numerical simulation of vertical pullout of plate anchors in clay

The behavior of strip and circular plate anchors during vertical pullout in uniform and normally consolidated clays was studied in this paper by means of small strain and large deformation finite-element analyses. Both fully bonded (attached), and "vented" (no suction on rear face), anchors were considered. The current numerical results were compared with existing laboratory test data, finite-element results, and analytical solutions. This study showed that, in small strain analysis, the scatter of existing data was mainly due to the effect of soil stiffness. In large deformation analysis, when soil and anchor base were attached with suction, the pullout capacity factor formed a unique curve independent of the soil strength (s(u)), soil effective unit weight (gamma(')) and anchor size (B=width of strip anchor and D=diameter of circular anchor). The transitional embedment depth ratio, H-SD/B or H-SD/D, (where H-SD=transition depth between shallow and deep embedment) was 1.4 for a strip anchor and 0.75 for a circular anchor. The ultimate pullout capacity factors (N-c) for deep embedment were 11.6 and 11.7 for smooth and rough strip anchors and 13.1 and 13.7 for smooth and rough circular anchors, respectively. However, when the anchor base was vented, the soil stayed attached to the anchor base for deep embedment, and the pullout capacity was therefore the same as for the attached anchor. The separation depth ratio, H-s/B or H-s/D, (where H-s=embedment depth at which the soil and anchor base separated) was found to increase linearly with the normalized strength ratio, s(u)/gamma B-' or s(u)/gamma D-'.