Some soils look firm when dry but change sharply when exposed to water. Ground conditions in the Kingdom range from earth to rock to sabkha, so knowing the soil type before founding is an essential step.
The illustration shows the three types covered here: collapsible soil (left), expansive soil (centre) and sabkha (right).
Collapsible soils
They hold together when dry but can settle suddenly when wetted under load. The laboratory collapsibility test reveals them.
Expansive soils
Usually clays, they swell when their moisture rises and shrink as they dry, moving foundations and floors and sometimes causing cracks. The free swell and swelling pressure tests measure this behaviour.
Sabkha soils
Saline soils found mostly near groundwater level, which may have low bearing capacity. They contain salts that can attack concrete and reinforcing steel.
Chemical tests
- Soluble salt content.
- pH.
- Chloride ions.
- Sulfate ions.
- Magnesium ions.
These results help in choosing the cement type and protecting buried concrete. Depending on the case, the geotechnical study may recommend replacing or treating the weak layer, or changing the foundation type.