Influence of Dilation Angle on Drained Shallow Circular Anchor Uplift Capacity

An experimental study of uplift capacity of 22 circular helical anchors installed in sand with peak friction angles between 40 and 50 degrees was performed. Laboratory triaxial tests indicated that the dilation angle varied between 10 and 25 degrees for these peak friction angles. To account for soil behavior exhibiting nonassociated flow (NAF), in which the dilation angle is much less than the friction angle, a limit equilibrium plane strain analytical solution for plate anchor uplift was updated and extended to axisymmetric conditions. Anchor test results were compared with upper bound (UB) plasticity solutions (based on associated flow) and the newly developed NAF limit equilibrium model. The UB solution overpredicted uplift capacity by more than a factor of 2, whereas the limit equilibrium model had a ratio of calculated to measured capacity of 1.15 and a coefficient of variation of 0.14. Although additional study is warranted, the consistency among the numerical, analytical, and experimental results gives confidence in the further application of the NAF limit equilibrium analytical solution presented in this paper.