Following a number of recent audits SER has become aware of the increased use of Ground Screw piles as an alternative to conventional foundation solutions for residential projects up to two storeys in height.
Certifiers should be aware that for the purposes of certification their approach should be no less onerous as if this were a more traditional piling system.
Prior to certifying, Certifiers should see that an appropriate Ground Investigation has been carried out to a recognised methodology in which the soils testing and narrative are relevant to ground screw piles. Certifiers should also ensure that the design has been carried out by competent persons and checked as appropriate prior to review and certification.
In addition, Certifiers should see that the following factors have been considered in the design:
- The reported soil conditions
- The possible impact of frost susceptible shallow soils
- The assessment of load-sharing between piles may need to reflect the absence of rigid spreader foundation at the pile heads
- The environmental conditions and the material specifications
- The site testing requirements, methodology and relevance to the pile type and design
- Long term settlement performance as derived from static load testing
As with other piling techniques, the use of the Schedule 1 process is also permitted here, but Certifiers should be aware of the following:
- The warrant drawings must include a layout of the screw piles and the loading requirements.
- The layout must be supported by preliminary design calculations or other justification to demonstrate the adequacy of the ground screws. Notwithstanding the basic design requirements noted above, other justification may include certification from a recognised testing authority which is appropriate to the particular project location, applied loads and ground conditions.
- The warrant submission must include a comprehensive performance specification, including appropriate site testing requirements. This may be a stand alone document or may be in the form of notes on the warrant drawings.
If the Certifier chooses to rely on the competence of an identified third party, they should consider whether they are competent to certify the project in the first place. If the decision remains to rely on a third party’s competence, the party reviewing the screw pile design should do so on behalf of the Approved Body. It would not otherwise be appropriate to rely on the competence of the specialist designer for the purposes of certification of this element as there is no direct contractual relationship between the Approved Body and the Specialist Contractor.
In all cases, Certifiers should maintain suitable records of the certification process which demonstrate that compliance with the Standards has been established.