Geotechnical categories
The principle
Section titled “The principle”Not every task calls for the same investigation. A simple, small building on known, good ground needs different treatment from a complex structure in difficult ground conditions.
Eurocode 7 handles this with categories: the category determines what depth of investigation, which tests and which design procedure are required.
What affects the classification
Section titled “What affects the classification”- the size and significance of the works,
- the complexity and how well known the ground conditions are,
- the groundwater situation,
- the environmental risk: neighbouring buildings, services, slopes,
- the sensitivity of the structure to movement.
What it means in practice
Section titled “What it means in practice”In the simpler case
Section titled “In the simpler case”Known ground conditions, a simple structure, low risk: less investigation, use of empirical relationships, simpler verification.
In the more complex case
Section titled “In the more complex case”Detailed investigation, laboratory testing, verification by calculation, and sometimes the observational method during construction.
In the special case
Section titled “In the special case”Bespoke testing, expert involvement, monitoring during construction.
Where light gauge steel comes into this
Section titled “Where light gauge steel comes into this”Low load does not automatically mean a lower category
Section titled “Low load does not automatically mean a lower category”The category follows from the whole situation: on poor ground a light building can also be a complex task, especially on a slope or with a high water table.
Uplift is a question in its own right
Section titled “Uplift is a question in its own right”Where the anchorage bears on the ground — with ground screws, say — the tension is a geotechnical question. Load testing and verification.
Sensitivity to movement
Section titled “Sensitivity to movement”An accurately manufactured, stiff structure is more sensitive to differential settlement. That is a consideration in the classification too.
Who decides it
Section titled “Who decides it”The geotechnical engineer, from the ground investigation report, in discussion with the structural engineer. This is not an administrative classification: it determines how much investigation is needed and what it costs.
The point
Section titled “The point”The geotechnical category says how much we have to know about the ground. The more uncertain the situation, the more — and that is always cheaper than fixing it afterwards.