Before using a DIY screw pile we 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 the structure?
The weight of the 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 when compared to a large summer house that will be used as a garden gym like this one.
How far do you want to space your DIY screw piles?
DIY screw pile spacing questions include: Do you want a pile every 2 metre? Then, is your construction 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 in a horizontal U bracket = 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 ‘the point break resistance in the soil’ on the measured layers?
You will need to consider the type of soil you will be using the screw piles in, as this will also determine the size and length of pile needed. Clay and chalk for example will produce different load bearing capacities and may require significantly different pile specifications.
Is the construction catching wind pressure?
Think about walls of a garden house or green house … Here we do not only need to think about vertical loads coming down on the pile, here you have horizontal forces at play on the piles. The higher they are above ground level, the bigger the risk of being pushed sideways. Even if we have a good layer on 50 cm of depth, immediately we would consider using at least a 120 cm pile.
What about the upwards moving forces?
This is relevant when calculating the wind pressure underneath ground mounted solar panel installation or a tent. The weight is not important here. The upwards wind pressure is the 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, go deeper to a better layer, or increase the helix diameter, to improve the load bearing capacity.
If you need any help with regards to you project…
… please contact us