9.1. Coarse grained soil behavior.

In coarse grained soil, single grained structure is maintained.

Coarse grained soil consists of larger particles that tend to be well-drained and have spaces between them. The term 'single grained structure' refers to the fact that each grain acts independently without aggregating into larger clumps. This structure is critical for understanding how coarse soils behave under stress and when subjected to water flow.

Think of coarse grained soil like a bowl of marbles. Each marble can roll around independently, much like how each grain can shift and move without being held tightly together. This independence allows water to flow easily through the spaces between the marbles, just as water flows freely through coarse soils.

In composite soil, behaviour depends on composition.

Composite soil is a mixture of different types of soil, such as coarse and fine-grained soils. The behavior of composite soil varies according to the proportions of each type of soil it contains. For instance, a composite soil with a higher proportion of coarse grains will exhibit characteristics similar to coarse soil, such as better drainage, while one with more fine grains will behave more like fine-grained soil, which retains water and has lower permeability.

Imagine making a smoothie with different fruits. If you use mostly bananas (fine), your smoothie will be thick and creamy, whereas if you use more strawberries (coarse), it will be thinner and more fluid. Just as the composition of fruits alters the texture and flow of your smoothie, the relative amounts of coarse and fine soils dictate how the composite soil behaves under various conditions.

Addition of water increases lubrication and transforms the structure into dispersed structure.

When coarse grained soil is moistened, the water acts as a lubricant between the grains, which can alter the way the soil behaves. Instead of the grains sitting independently like marbles, they can move more freely past one another, changing the soil structure into a 'dispersed structure.' This change can affect the soil's strength and stability, particularly when loaded or compacted.

Think of how wet sand behaves differently from dry sand. On a beach, dry sand can shift and flow easily when you try to build a sandcastle, but once it's wet, the grains stick together better. Similarly, adding water to coarse grained soil changes its behavior, sometimes making it less stable if too much water is added.

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