Before using a DIY screw pile you should ALWAYS look at the following points
When using DIY screw piles, it’s important that you know certain key factors to decide which type or length of the screw piles you will need.
What is the weight of your structure?
The weight of your structure will determine the size and length of the screw piles you need. Obviously a small light shed used for garden tools will have different requirements compared to a large summer house that will include a gym like this one.
How far apart should you place your DIY screw piles?
Imagine spacing your piles every 2 metre. Will your base be rigid enough to make the bridge between the 2 piles? The basic rule for a terraces is: height of the wooden beam x 20 = maximum distance between the piles. A beam with dimension 5 cm x 15 cm looks like this:
15 cm x 20 = a max distance of 3 metres between the sustaining piles.
Or, you may prefer to work with 5 x 10 cm? OK, 10 cm x 20 = a max distance of 2 m between the sustaining piles.
What is your point break resistance in the soil?
You will need to consider the type of soil you will be working in, as this will determine the size and length of pile needed. Clay and chalk for example will produce different load bearing capacities for screw piles and may require significantly different pile specifications. Put simply, if you are screwing in to loose soil conditions you will have to go deeper when compared to stiff soil conditions.
Will your construction catch wind pressure?
With a large garden or green house you do not only need to think about vertical loads coming down on the pile, you may also have horizontal forces at play on the piles. The higher they are above ground level, the bigger the risk of being pushed sideways by winds. In this case it worth make allowances for the lateral load and taking extra provisions with pile depth.
What about the upwards moving forces?
This is relevant to you when calculating the wind pressure underneath ground mounted solar panel installations or a tent. The weight of your structure is not so important here. The upwards wind pressure maybe your biggest challenge. If your formula tells you that there is an upwards pressure, in case of a storm, of, let’s say 10 tons, and you have 20 screw piles installed … that means each pile would need to resist a pulling force of at least 0.5 tons. With 120 cm Screw pile or longer, the calculated bearing capacity, split in 2, gives you a rough idea of that resistance. In this example (0.5 tons upwards resistance), you will need a layer where your piles have a bearing capacity of at least 1 ton. If not, you need to go deeper to a better layer, or increase the helix diameter, to improve your load bearing capacity.
If you need any help with regards to you project…
… please contact us