The correct answer is: The minimum depth of foundation in clayey soils is 0.9 m.
Clayey soils are relatively impermeable, which means that they do not allow water to flow through them easily. This can cause problems for foundations, as
the water can build up and cause the soil to expand and contract. This can lead to the foundation settling or cracking.To prevent these problems, it is important to place the foundation below the frost line. The frost line is the depth at which the soil freezes in the winter. If the foundation is not below the frost line, the freezing and thawing of the soil can cause it to move and damage the foundation.
In clayey soils, the frost line is typically about 0.9 m deep. Therefore, the minimum depth of foundation in clayey soils is 0.9 m.
Option A (0.5 m) is not deep enough to be below the frost line in clayey soils. This could lead to problems with the foundation settling or cracking.
Option B (0.7 m) is deep enough to be below the frost line in most clayey soils. However, in some areas with particularly cold winters, it may be necessary to go deeper than 0.7 m.
Option C (0.9 m) is the minimum depth of foundation required in clayey soils. This is deep enough to be below the frost line in most areas and will help to prevent problems with the foundation settling or cracking.
Option D (1.2 m) is deeper than the minimum depth required in clayey soils. However, in some areas with particularly cold winters, it may be necessary to go deeper than 1.2 m.