Axial testing and numerical modeling of square shaft helical piles under compressive and tensile loading

Abstract

Helical piles are increasingly used to support and rehabilitate structures subjected to both tensile and compressive axial loads. This paper presents a detailed investigation into the axial performance of helical piles. The study encompasses 19 full-scale load tests in different soils and numerical modeling using finite element analysis. The ultimate load criteria and load transfer mechanisms for helical piles were examined. In addition, the relationship between the installation effort (torque) and pile capacity was explored to determine its suitability for predicting pile capacity. The piles tested were made of three circular pitched bearing plates welded at a spacing of three helical diameters to a solid-square, slender steel shaft. It is proposed to determine the ultimate pile capacity as the load corresponding to pile head movement equal to 8% of the largest helix diameter plus the pile elastic deflection. A torque correlation factor, KT = 33 m–1 for compression and KT = 24 m–1 for uplift, was established to relate the ultimate pile capacity to the installation torque. It was found that load transfer to the soil is predominantly through a cylindrical shear failure surface that follows the tapered profile of the interhelices soils and the bearing capacity of the lead helix in the direction of loading.

Geotechnical Behavior of Helical Piles Via Physical Modeling by Frustum Confining Vessel (FCV)

“…Sakr (2011) reported that uplift capacity of helical piles is about 80% of compressive capacity, but, Livneh and El Naggar (2008) had reported fewer values of uplift capacities. They proposed a failure criterion to predict the ultimate load for the helical piles.…”

Behavior of Helical Piles – As a Geoenvironmental Choice – – By Frustum Confining Vessel

“…They proposed a failure criterion to predict the ultimate load for the helical piles. The ultimate load is defined as the load associated with deflection equal to 8% of the diameter of the largest helix plus the elastic deflection of the pile [17].…”

“…3. a) Schematic of the FCV, b) Idealized distribution of stresses within control volume [17] to which it is pressurized. Sedran (1999) reported the factors relevant to FCV in his research [18].…”

Performance Assessment of Screw Piles Embedded in Soft Clay

“…The screw piles were initially used primarily as anchors, and therefore focused on tensile loads such as transmission tower sand buried pipelines. However, their use has been extended to structures that are subject to compressive, tension and lateral loading [13]. The screw pile system is not suitable for the foundation in gravely or stiff soil, as the helix plates can be damaged during the process of pile installation.…”