An effective stress theoretical model for shear resistance and adhesion factor of dynamically installed anchors

This paper proposes a theoretical effective stress model for estimating the shear resistance and the time-dependent adhesion factor of dynamically installed anchors. The anchor installation process is approximated by a cylindrical cavity expansion process and the residual friction at the soil–anchor interface is assumed to be fully developed. The shear resistance and adhesion factor just after installation are first determined by consideration of the short-term changes in total stresses and excess pore pressure around the anchor. This allows the short-term effective stress state of the soil around the shaft to be evaluated. For a finned anchor, the circumferential stresses on the fins are considered explicitly. The time-dependent adhesion factor is then evaluated by consideration of the changes in total stress and pore pressure in the vicinity of the anchor during post-installation consolidation. Reasonably good agreement is obtained between the predicted results and the results of centrifuge model tests, as well as commonly recommended methods. Finally, a simplified procedure for estimating the total shear resistance and adhesion factor approximately is proposed, which simplifies the evaluation of the mathematically complex functions and allows a quicker estimation of the adhesion factor and shear resistance. An important finding in the study is that the fins are less efficient in mobilising interface friction than the shaft because the effective circumferential stresses are invariably lower than the effective radial stresses. As a result, the shear resistance that can be mobilised by the fins is correspondingly lower.