The limits of ground screws
Where the ground does not allow it
Section titled “Where the ground does not allow it”Stony, rubbly layers
Section titled “Stony, rubbly layers”Installation can meet an obstruction, and the element can deflect or be damaged. The obstruction is not visible from the surface.
The element cannot penetrate to the depth required.
Heavily made ground of unknown composition
Section titled “Heavily made ground of unknown composition”The capacity is unpredictable, and foreign matter in the fill forms an obstruction.
Very soft, compressible layers
Section titled “Very soft, compressible layers”If the bearing stratum is deep, a longer element is needed — possible, but this is where economy runs out.
Aggressive ground chemistry
Section titled “Aggressive ground chemistry”The corrosion load is higher, which affects the service life.
What remains a design question
Section titled “What remains a design question”Corrosion and service life
Section titled “Corrosion and service life”Steel in the ground sits in a corrosive environment. The coating, the material thickness and the design life have to be handled together.
Frost action
Section titled “Frost action”The element has to provide capacity below the frost depth, or freezing can lift it. Frost depth.
The floor construction
Section titled “The floor construction”With ground screws the floor is not a ground-bearing slab but a suspended structure on joists. That has building-physics consequences: the space beneath the floor is ventilated, so the insulation and vapour control follow a different logic.
Thermal bridge
Section titled “Thermal bridge”The connection between the steel element and the structure can form a thermal bridge, which has to be handled in the detail.
What to know on the verification side
Section titled “What to know on the verification side”Capacity cannot be estimated: the ground investigation, the technical assessment belonging to the product and — where warranted — a load test together provide the basis for the design. Load testing and verification.
When they are the right choice anyway
Section titled “When they are the right choice anyway”- where fast, dry construction is needed,
- where uplift has to be resisted,
- in a sensitive environment, with little earthwork,
- for a temporary or removable structure,
- on a site that is hard to reach.
The point
Section titled “The point”Ground screws are a good solution — where the ground allows it. So the first step is not the order but the ground investigation.