Stresses and strains around helical screw anchors in sand

Abstract

Experimental investigation on stress development in sand due to installation and uplifting of helical screw anchors is presented. Five model anchors with different geometry were tested to examine the effect of screw shape on stress development in sand. The sand was placed in layers and mechanically compacted by a hand-held air hammer. The testing tank was equipped with stress transducers located at predetermined positions to allow measuring the stresses in the sand around and in the near vicinity of the installation path. Stress transducers were oriented such that vertical and lateral stresses could be measured. Anchors were installed into layers of dense, medium, and loose sands. Stress measurements indicated that the tested sands were slightly overconsolidated due to the utilized placing technique. Furthermore, measured stresses were used to determine the extent of stress field inside the sand. Deflections of sand surface, during pullout load application, were measured by displacement transducers. The stresses measured within the sand together with the recorded surface deflections were utilized to establish the extent of the mechanism of failure for shallow, transit, and deep anchors.