Field and numerical studies on bearing capacity of helical screw piles in Caspian Sea coast soil

The installation of driven piles in urban areas encounters various challenges due to several installation requirements concerning vibration, noise pollution, adjacent structure protection, and access to heavy traffic areas. Novel helical piles resolve these challenges and reduce soil disturbance. The present study conducts a field study of helical, self-expanded, drilled displacement steel piles, and driven piles with an embedment depth of 3.2 m. The piles were subjected to static compressive loading tests. It was found that the helical and self-expanded piles had approximately 70% higher bearing capacities than the driven pile at a displacement as large as 5% of the pile diameter and can be efficient and effective alternatives to driven piles in urban and coastal constructions. Then, numerical simulations were performed using the finite element method to explore the effects of soil layers on the bearing capacity of helical piles and the soil failure mechanism. It was found that soil layers significantly affected the bearing capacity of a helical pile and would change the cylindrical failure mechanism into the individual failure mechanism. Furthermore, a rise in the clayey soil depth could substantially influence the bearing capacity of a helical pile.