Load testing and verification

Why verification is needed

Because the properties of the ground vary from point to point, while the design works with characteristic values. The actual capacity emerges at the place of installation.

That is the nature of geotechnics: here the construction is also a measurement.

The load test

What it does

The element is loaded with a known, gradually increased load and the movement is measured. The result is a load–displacement curve from which the capacity can be established.

When it is warranted

• where the ground conditions are uncertain,
• where the capacity is critical in the design,
• where many identical elements are installed and the result can be extended to the whole series,
• where the tension capacity governs.

What it gives

Far stronger evidence than calculation, because it measures the behaviour of the real ground and the real element.

Installation torque

With ground screws the torque measured during installation correlates with the expected capacity. That is valuable because:

• it is available for every element, not only the one load tested,
• it immediately signals where the ground differs from expectations,
• it can be recorded, so it can be retrieved afterwards.

If an element goes down at a lower torque than expected, that is a warning: the ground is weaker there.

What has to be recorded

• the position and identifier of the elements,
• the installation depth,
• the torque measured,
• the results of the load tests,
• the deviations and the action taken.

This is part of the foundation documentation, and irreplaceable at a later extension or in a dispute. Handover documentation.

The observational method

In complex cases the geotechnical standard allows the design to be based on measurements during construction, with thresholds and an intervention plan set in advance. That is not improvisation but a regulated procedure.

The point

With the ground, the evidence is the measurement. One load test is worth more than any detailed calculation — and the installation data gives the rest for free.