Analysis of pullout bearing capacity of enlarged head anchors and soil failure modes using discrete element method

Enlarged head anchors are commonly used in the anti-floating of underground structures and foundation pit support, where the anchoring force is increased by full contact between the enlarged head section and the soil. However, there is still a significant lack of research on the pullout tests of enlarged head anchors at various section inclinations, which potentially hinders the engineering application of this promising geotechnical anchoring method. This study employs the Discrete Element Method (DEM) to conduct pullout tests of the enlarged head anchors at four enlarged head section inclinations and three confining pressures. The results indicate that the load-displacement curves of the enlarged head anchors initially increase sharply and then slightly decrease before eventually entering a stable stage. The enlarged head anchor with a section inclination of 120° exhibited superior bearing capacity during pullout tests. An increase in confining stress was found to enhance the mobilization of the bearing capacity of the enlarged head anchor. At the smaller section inclination of the enlarged head, the bearing capacity primarily originates from the end resistance generated ahead of the enlarged head. As the section inclination increased, the frictional resistance along the anchor-soil shear interface progressively became the dominant contributor to the bearing capacity. The observed contact force chain structure ahead of the enlarged head was considered evidence of arching effect formation. The critical role of the soil arching effect in mobilizing the pullout force of enlarged head anchors is emphasized.