Screw Piles

Undoubtedly, when choosing a foundation for a house, we want to be sure of its reliability and that in a few years we will not see cracks in our walls.

However, the cost of a reinforced-concrete foundation makes us look for alternatives. How do we find an option that does not affect the stability and reliability of our house?

One such option is a foundation on screw piles.

Perhaps you are hearing about such a foundation for the first time and have already begun to doubt its reliability. Let us look at how it is built and what is taken into account when choosing it.

In fact, screw piles are not a new invention. They have been used in construction for a long time.

How screw piles are built

A screw pile is a tubular steel shaft with one or more helical blades. The pile is driven into the ground by screwing, in some cases with pilot holes. The blade transfers the load to the soil and resists pull-out of the pile. The installation technology depends on the soils and the design of the pile.

The appearance of the exposed part of the foundation can be taken into account in the design of the plinth.

What is taken into account when choosing

Screw piles are set down to a layer of soil capable of carrying the load. The depth, blade sizes and length of the piles are selected on the basis of engineering-geological surveys and calculation. On frost-heaving soils the stability of the piles under frost-heave forces is also checked.

Whether screw piles can be used on a particular plot — including with weak or waterlogged soils and on a slope — is established by the surveys and the design project.

Installation and start of loading

The method of installing screw piles and the equipment needed depend on the diameter and length of the piles and on the soils; the quality of installation is monitored in accordance with the design.

Steel screw piles do not need concrete to harden, but the permissible load and the moment loading may begin are set by calculation. If the foundation includes concrete elements that take part in carrying the load (for example, a concrete grillage), they are loaded after the concrete has reached the required strength. Whether loading must be delayed when the steel shaft is filled with concrete depends on the designer's decision.

Installing steel piles is not tied to concrete hardening, but in winter the work is affected by ground freezing and by conditions on the plot. Concrete work in cold weather requires measures to protect the concrete from freezing. Whether work is possible in the cold season is decided by the designer and the contractor.

Durability

The service life of steel screw piles depends on the aggressiveness of the soils, the presence of stray currents, the wall thickness and the protective coating. Galvanizing and painting are examples of protective coatings, but whether they are sufficient depends on the operating conditions; the method of corrosion protection and the design service life are chosen with these conditions in mind.

In some cases screw piles can be dismantled and reused. Whether they can be extracted and reused is assessed taking into account the condition of the piles, the conditions of dismantling and the requirements of the new project.

For other foundation options for a straw-panel house, see the overview: Foundation for a Straw-Panel House.