Testing ground screws for building regulations/Load Testing
When you’re installing a structure that needs to comply with building regulations, you may be required to provide empirical data to show the load capabilities of the ground screws across the proposed site. We can do this in two ways:
The first is for our technician to install the size of ground screw that you wish to use and then test its capabilities.
The second is for you to tell us what load capability you are hoping to achieve, and we will start by installing the size that we think you will need. We’ll then test that ground screw to find the failure point, if the failure point is too low then we’ll repeat the process with a larger ground screw. We’ll carry on doing this until we get the required result. If we find that the ground just isn’t able to carry the load required for the proposed number of ground screws, you’ll need to increase the number of ground screws to reduce the load on each one.
The usual way to test the capabilities of a ground screw is with a pull test, but there are two other tests that may be required either as well as or instead of pull testing a ground screw.
How do we test ground screws?
Pull Testing
A single ground screw is installed. We place a load spreading plate over the ground screw and attach a ram to the ground screw. Using a calibrated pump we exert upward pressure on the ground screw for a set period and measure the movement. The pressure used and the amount of movement is recorded. The pressure is released and then applied again after a set period, but this time at a higher pressure. This is repeated until the ground screw moves sufficiently that it has been deemed to fail. The test is repeated across the site, the number of tests conducted is either according to the size of the site or the client’s wishes. The results are recorded, and an industry standard calculation is applied to the results which give a final load figure as an average across the site.
Push, Load, or Compression Testing
Multiple ground screws are installed in a line with a single ground screw in the centre, this is the ground screw to be tested. A beam is installed and bolted to all the anchor ground screws and a ram is placed between the ground screw to be tested and the beam. Using calibrated equipment, pressure is applied to the ram in stages and any movement in the centre ground screw is measured. If required, the beam can simultaneously be measured to ensure that any deflection is noted. The point at which the ground screw moves into the ground beyond a predetermined point is the load at which it is deemed to have failed. The test may be repeated across the site, the number of tests conducted is either according to the size of the site, the structural engineer requirements, or the client’s wishes. The results are recorded, and an industry standard calculation is applied to the results which give a final load figure as an average across the site.
Torsion Testing
Multiple ground screws are installed to provide an anchor for the ground screw to be tested. The equipment is attached and, using calibrated equipment, a ram is used to pull the ground screw sideways. This is conducted repeatedly until the ground screw has moved sufficiently that the test is deemed to have failed. The test is repeated across the site, the number of tests conducted is either according to the size of the site, the structural engineer requirements, or the client’s wishes. The results are recorded, and an industry standard calculation is applied to the results which give a final load figure as an average across the site.
All the test results are provided as a report including site details, the test point location, the method used, and the actual test result to EN 9997-1 (Geotechnical design Part 1: General rules) and EN 1997-2 (Geotechnical design Part 2: Soil survey and testing).