Effect of Helical Surface Area on the Performance of a Multi-Helix Anchor

Abstract

Anchoring temporary shelters is a repetitive and time-consuming task mostly accomplished by hand or handheld tools. Therefore, such anchors should be lightweight and easy to install. Experimental investigations on the effect of anchor geometry on ease of installation and uplift capacity of a double-helix anchor are presented. The double-helix anchor with 1.78 kN uplift capacity was tested on various soil types and conditions. Similar tests were carried out using the same anchors except that the helices were perforated for the first test and notched for the second test. The experimental setup was arranged to allow measurement of installation torque, installation time, and pullout load. It was observed that the uplift capacity and weight of the anchor dropped with the reduction in the surface area of the helices. The drop in the uplift capacities of the anchor with perforated helices and that with perforated and notched helices were 1.05 kN and 1.2 kN, respectively. Weight loss of 0.45 kg due to perforation and 0.88 kg due to notching were recorded. The minimum uplift capacity of the anchor with both perforated and notched helix was 1.84 kN. The ease of installation of the anchors was assessed based on the anchor driving torque and installation time. A general trend of reduction in the magnitude of anchor driving torque and installation time with the reduction in helix surface area was observed. Thus, perforating and notching helix surfaces could reduce the anchor weight and improve drivability.