DRIVABILITY AND PULLOUT RESISTANCE OF HELICAL UNITS IN SATURATED SANDS

Abstract

The results of an experimental investigation on the drivability of helix-shaped units into submerged sand and sand subjected to upward seepage flow are presented. In this research study, the helical units are used as structural anchoring elements. A testing program is conducted to study the effect of water existence in a sand deposit on the driving moment (torque) required to install helix-shaped units, with reference to torque required to install the same in dry sands. Dense sand is used in this study with water conditions varying from hydrostatic pressure to upward seepage flow with three different velocities. Measurements are recorded for the installation torque versus depth of installation. Based on the results of this study, it is concluded that the existence of water in the sand bed material facilitates the installation and reduces the torque required to drive the helical units. It is also found that helix drivability improves with the increase of the velocity of seepage flow, however, this seepage flow negatively reflects on the resistibility of these units to pullout forces. It is recommended that the design of both the driving technique and the pullout resistance of helix-shaped foundation units be balanced in a way that the easiness of installation and the obtained pullout resistance are optimized. It is also recommended that pullout resistance of anchors should not be compromised to achieve higher drivability.