There are 3 primary screwpile to structure connection methods. We call this the interface method.
The pilehead is CAST into a concrete pile cap or footing.
The pilehead is WELDED directly to the structure.
The pilehead is BOLTED to the structure. How you connect to a screwpile will be governed firstly by whether the applied load is in compression or in tension and secondly, by the application the pile is being used for.
The type of interface used will depend on:
whether the structure being supported has a sub-structure foundation system
type of foundation system
type of structure being supported
type of loads (compression, tension, horizontal) to be resisted
whether the structure is permanent, semi-permanent or temporary
whether structure relocation is likely and therefore the screwpiles need to be reusable
environmental and safety issues
economics and budgets
practicality and simplicity
Casting the head of the screwpile into a concrete footing, as is usually the case for domestic housing construction, or into pilecaps used for larger design or column loads, is the most common and cost-effective method of connecting screwpiles to a structure's foundation system (assuming the structure has one). The screwpile head may have components that are shop welded for use as part of the casting interface. Alternatively cast-in bars may be required to transfer the structure's design loads through to the screwpile to eliminate localised concrete crushing around the pilehead. The interface is part of the screwpile engineering design service that is included. It is important to have sufficient concrete cover around the screwpile interface head so that pile breakout or punching shear of the concrete does not occur when full load capacity is utilised.
Welded connections can be direct or via a steel plate or bracket interface. In some applications the interface plate can be used as the pile driving connection plate. This is particularly useful in reducing onsite work as the drive plates shop welded can be an economical solution.
Bolted connections are considered appropriate for lightweight structures. These include transportable type buildings (donga's), mid-sized towers, tapered steel lightpoles, signs, awnings and temporary structures.
It is important to consider the allowable installation + and - tolerances that will occur in line with the ground conditions, installation equipment and operator experience when choosing the interface option.