Abstract

Helical piles are increasingly adopted where foundations must resist uplift while permitting rapid installation andimmediate loading. This paper presents a laboratory investigation of the pull-out response of model helical piles installed in sand,with emphasis on helix number, embedment ratio, and soil compaction. Four 700-mm-long mild-steel model piles were examined:a plain shaft (P) and piles with one, two, and three helices (P1–P3). The shaft diameter was 15 mm, helix diameter 75 mm, helixthickness 2 mm, pitch 15 mm, and helix spacing 100 mm. Pull-out tests were performed in a 750 mm × 1000 mm × 1000 mm tankusing a rope-and-pulley loading arrangement and a dial gauge of 0.02 mm resolution. The sand had a reported specific gravity of2.54. At H/D=2.5 in loose sand, ultimate loads for P, P1, P2, and P3 were 2.873, 8.681, 17.238, and 20.731 kg. Increasing embedmentto H/D=3.5 raised the corresponding capacities to 3.442, 16.105, 20.734, and 28.171 kg. Under compacted sand at H/D=2.5, P1–P3reached 13.259, 39.883, and 45.535 kg. The results show that additional helices, greater embedment, and increased soil densitysubstantially enhance uplift resistance in the tested model system.Index Terms—helical pile, screw pile, pull-out capacity, uplift resistance, sand, embedment ratio, compaction