The correct answer is D. Black cotton soil is unsuitable for foundations because its property to undergo a volumetric change due to variation of moisture content.
Black cotton soil is a type of clay soil that is found in many parts of the world. It is characterized by its dark color, high organic content, and high plasticity. Black cotton soil is a very difficult soil to work with, and it is often unsuitable for foundations.
One of the main problems with black cotton soil is that it undergoes a large amount of volumetric change due to variation of moisture content. When the soil is dry, it shrinks and becomes very hard. When the soil is wet, it expands and becomes very soft. This volumetric change can cause problems for foundations, as it can lead to cracking and settling.
Another problem with black cotton soil is that it is very compressible. This means that it can be easily compacted, which can also lead to problems for foundations.
For these reasons, black cotton soil is often unsuitable for foundations. If you are considering building a foundation on black cotton soil, it is important to consult with a geotechnical engineer to determine whether it is safe to do so.
Here is a brief explanation of each option:
A. Bearing capacity is low: This is not the main problem with black cotton soil. Black cotton soil can have a high bearing capacity, but it is important to make sure that the foundation is designed to take into account the soil’s properties.
B. Permeability is uncertain: This is also not the main problem with black cotton soil. Black cotton soil can be either permeable or impermeable, depending on its composition. However, it is important to make sure that the foundation is designed to take into account the soil’s permeability.
C. Particles are cohesive: This is a characteristic of all clay soils, not just black cotton soil. Clay soils are cohesive because the particles are negatively charged, which causes them to attract each other. This cohesion can make it difficult to work with clay soils, but it also makes them strong.
D. Property to undergo a volumetric change due to variation of moisture content: This is the main problem with black cotton soil. Black cotton soil undergoes a large amount of volumetric change due to variation of moisture content, which can cause problems for foundations.