What is a Helical (screw) pile?

The GTL Helical (screw) pile foundation is an innovative and sustainable foundation solution. The helical pile, also known as the screw pile, consists of a central hollow shaft of differing diameters and sectional thickness, with helical plates strategically welded at given centres.

Design depth is achieved by bolting on additional shaft sections of differing lengths according to site and plant restrictions. The helixes are rotated into the ground to a pre-designed depth. Each helical plate on any single pile will be of the exact same pitch as one another. This minimises soil disturbance during installation compared with conventional piling techniques, such as CFA or Rotary bored. The diameter of the helical plates is governed by the pre-determined loading and soil condition. Loads are transferred to the soils by the helical plates and shaft friction. The overall number and spacing of the plates are designed to maximise the allowable load capacity of the soils.

The technology of the GTL helical pile foundation is not so much in the manufacturing of the product but rather in the specific engineering design, with the foundation being designed as a solution to a particular requirement or condition.

Helical piles are referred to as small displacement piles and designed in accordance with BS8004: code of practice for foundations or to the standards relevant to the specific country.

Until recently had only been used for 400kN SWL, however, through GTL’s continued R&D we are able to cope with much higher loads.

Installation

The Helical (screw) pile is rotated into the ground by means of a bi-directional auger, hydraulically powered by an excavator. Throughout the installation process GTL monitors the installation torque and pile alignment.

GTL monitor the installation torque for the following reasons:

• To provide a qualitative assessment of the soils being penetrated at various depths. The recorded installation torque and depth will be interpreted against the existing soil data, by way of a graph. By interpreting the soil data against the installation torque, a correlation can be obtained that enables a simple verification strategy to be determined.
• To maintain the integrity of the Helical (screw) pile during installation and to mitigate damage through exceeding torsional strength to any of the pile’s components. Each Helical (screw) pile has a maximum stress level and this must not be exceeded.