How long do ground screws last?

At No More Digging, we supply and install professional and extendable ground screw foundations from RADIX.

RADIX galvanises its ground screws to BS EN ISO 1461:2009, providing a zinc coating that protects the steel of each ground screw against the elements. We can calculate the life expectancy of our ground screw foundations based on the average corrosion rates of their galvanised coating and steel specifications.

galvanised ground screw foundations

The average corrosion rate of the zinc coating on galvanised steel is 6µm per year in typical soil conditions, as provided and verified by independent engineers. With RDX PRO RF140 76MM Ground Screws* being galvanised to 85µm, we can show 85 / 6 = 14 years.

Once the zinc coating has been exhausted, steel corrosion can commence at an average rate of 30µm per year.

Based on our RDX PRO RF140 76mm ground screws* having a 3.0mm thick wall and helix, this would take 60.6 years to reduce to a 1.0mm thickness.

That is not the end of a ground screw, however. Checked with 50% of the 70kN test load to represent the Factor of Safety of two that RADIX adopts, as illustrated below, a reduction to 1.0mm is still within the parameters of a safe working load for ground screws.

ground screw lifespan showing 35kN loading on 15mmx1mm reduced helix

FoS2: 35kN loading on 15mmx1mm reduced helix

ground screw lifespan showing full 70kN loading on 15mmx1mm reduced helix

Full 70kN loading on 15mmx3mm helix

Therefore, as evidenced above, the overall life expectancy of our ground screws is over 76.6 years.

* Life expectancy is calculated based on the RDX PRO RF140 M16 76×1550-T3.6 ground screw installed in typical soil conditions, with structural analysis documentation provided and verified by independent engineers.

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