Which soil type is least suitable for shallow foundations?

Explanation:

1. Black cotton soil (also known as expansive soil) is least suitable for shallow foundations because it has high shrinkage and swelling characteristics, especially when exposed to moisture.
2. These soils expand when wet and shrink when dry, causing instability in foundations and leading to cracks or shifting.

 Additional Information

1. Silty clay: While silty clay has low bearing capacity, it does not exhibit the same expansive behavior as black cotton soil, making it relatively more stable for shallow foundations.

2. Fine sand: Fine sand has good drainage properties, but its bearing capacity may be lower than coarser sands. However, it is generally suitable for shallow foundations if properly compacted.

3. Coarse sand: Coarse sand is suitable for shallow foundations as it has good load-bearing capacity and excellent drainage properties.