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All Helical (screw) pile and grillage designs are created in our technical department by our own in-house engineers.

Helical (Screw) Pile Design

Helical (screw) pile designs are developed by GTL’s in-house engineers taking into the account the performance specifications of the client and the available geotechnical information for the site.  The design of the GTL Helical (screw) pile utilises the same conventional geotechnical theory as used for the design of CFA or rotary bored piles.  GTL do not use torque as a basis of design and pile set. Torque versus soil stiffness is used on site to monitor variable soil conditions that may affect the performance of the piles. Piles are designed and plate spacing and depths set on consideration of the geotechnical site investigation information.

Helical (screw) piles can be designed to take into account compression, tension loads and load reversals.  The nature of the Helical (screw) pile is such that it accommodates the forces from expansive soils and negative skin friction. Lateral loads can be designed for using pile groups, single piles with larger diameter steel sections, and the centrifugal pile to enhance lateral capacity.

Grillages and pile caps

GTL design their grillages to meet the specific performance requirements of the structure that they will be supporting.  All our grillage designs conform to British Design Standards.  Designs can be adjusted to meet the design standards of other EU countries when required.


Corrosion of piles is assessed by studying the available soil investigation information, the contamination testing results and the soil resistivity readings.

If little or no information is available regarding the potential corrosion risk to the piles, a worst case scenario will be assumed based on the published guidance and estimated corrosion rates stated in BS8004 and Eurocode 3 Part 5 Steel Piling.

CAT 3 checks

CAT 3 Checks for work on Rail or Road can be carried out as part of our package of works, but RKD Consultants Ltd, an independent firm of Geotechnical Engineers will issue the certificates of compliance for the final issue of calculations and design drawings.


Pile testing is recommended to be performed on all sites but should only be carried out after taking into account the quality of site investigation information, the project programme and the number of piles.
GTL recommend that pile testing is performed on projects for which there are specific serviceability requirements or a requirement for proof of load carrying capacity.