The structure already exists.
In this case, geotechnics is used to generally determine the causes of a problem with the structure (such as visible cracks or displacement).
If the problem is not related to the soil, this helps to rule out this possibility, and it may be due to other factors, such as the structure itself.
If it’s related to the soil, often in older buildings, certain techniques can be implemented to address the issue.
In extreme cases, it may even be preferable to demolish and rebuild to current standards (often in cases where the structure is already too damaged).