Evidence for the load your foundation carries
The structure above places downward forces on its foundations. A physical ground screw compression test applies a controlled downward load and measures the response of the tested screw in the actual ground.
This is sometimes described as a push test or a load-bearing test. On this page, compression load testing means direct downward loading. If the phrase “load test” in your brief refers to a different direction or method, we establish that before arranging the visit.
A recorded load is considered alongside movement and the agreed test criteria. The information helps your project team review the proposed specification or assess the tested installation against its requirements.
Direct compression testing and calculated capacity
JustBases offers both physical downward testing and compression capacity calculations using pull-test results where the method is suitable. They can provide different kinds of evidence, so the basis of each value must be clear.
| Question | Physical compression test | Compression capacity calculation |
|---|---|---|
| How is the value obtained? | A downward load is physically applied and the resulting response is recorded. | A value is derived using pull-test results, relevant project information and an applicable calculation method. |
| What is reported? | The measured results for the agreed compression test. | The calculated value, its method and the basis applicable to the agreed project. |
| Can either be assumed for every site? | No. The test scope and locations must suit the foundation question. | No. Suitability of the calculation must be established; there is no universal pull-to-compression conversion. |
| How is the method chosen? | The required evidence and method are agreed for the actual screw, ground and project team’s requirements before work is confirmed. | |
A calculated compression capacity is labelled as calculated. It is not presented as though the screw was physically loaded downwards. If your engineer requires a direct compression test, tell us so that the scope addresses that requirement.
For the upward test itself, see our ground screw pull testing service.
Planning a useful compression test
Identify the foundation
Available screw specifications, proposed depth, layout and installation information help define what is being checked. For existing work, tell us who supplied and installed the screws.
Agree the loading requirement
The target load, stages, measurement and stopping criteria need to answer the designer’s question. We discuss these as part of the brief rather than assuming one programme suits every job.
Review the site arrangement
Access and space for the test setup matter, as do site features and the selected positions. Tell us about anything already built over or around the screws before the visit is arranged.
You do not need all this information to make an initial enquiry. Start with what you know; we will identify what else is needed before confirming the test scope.
Recorded results and a written report
During physical compression testing, the applied load and measured response form the test evidence. The written report records the agreed testing work and results, with load calculations where included in the scope.
The method used to obtain a value remains clear: direct downward testing, a calculation based on pull results, or another expressly agreed method. Share any report requirements from your engineer or project team when enquiring.
The number and locations of tests are agreed for the site. A result at one point does not make variable ground uniform, and a tested capacity is not automatically a working load for every screw in a different arrangement.
Testing separately or alongside installation
We offer standalone load testing, including work involving other suppliers’ or installers’ ground screws. Buying a complete installation from JustBases is not a condition of making a testing enquiry.
If you also need the foundation installed, we can discuss the test, any calculations and the installation sequence together. The written quotation defines the scope and responsibilities.
See ground screw installation or our trade foundation service for the wider work available.
Compression is one part of foundation performance
A downward load test does not independently establish uplift, lateral or twisting performance. Where a specialist project needs lateral testing, torsional testing or recorded installation torque, these are available by arrangement within a suitable brief.
Installation torque records turning resistance rather than directly applying a downward load. Any use of those readings to inform capacity needs an appropriate basis for the screw and site. It should not be treated as an automatic substitute for the physical test the project requires.
Test results and calculations provide evidence for the project team. They do not guarantee Building Control approval or replace the complete design. Tell us about the relevant designer’s or approval body’s requirements before the work is agreed.