The Effect of Installation Torque on The Behavior of Helical Piles under Tension Load Tested in Centrifuge Device

Screw piles have good compression and tension capacity and can be used for different soil strata under and over water. As well as to the screw pile has low cost and quick installation comparing with other piles. Screw pile foundations are also referred to as torque piles helical anchors, screw anchors, piers, or helical piles. To makethe behavior of stress-strain of the soil in the centrifuge similar to that exists in the sitea centrifuge modelling must be considered.New centrifuge device for installation and testing screw pile models is designed and manufactured with different velocities depending on the value of N (gravity scaling factor) and applying compression, uplift and inclined loads during rotation and control them electronically. The new installation system for helical piles used in this device is to install each pile with different torque from other depending on its capacity. The relative density (R.D) of sandy soil used in this study is 55% and the helical pile models with 40 mm diameter, the spacing ratio (S/D) of 1, 1.5, and 3 and different number of helices of (one and two helices). All tests of screw pile models are performed in centrifuge device at 10-g undertensionload. The installation torque causes a soil disturbance and this disturbance increases as the installation torque increases. For the cylindrical failure mechanism, the reduction percentages of the uplift capacity of the helical pile with double helix S/D =1 are 15% and 26 % while it is about 10% and 21% in the case of S/D =1 respectively.