Explanation:

Granular soil: Granular soil consists of individual particles or grains, such as sand or gravel. These particles have a relatively high void ratio, meaning there is a lot of space between the particles.

Void ratio: Void ratio is the ratio of the volume of voids (empty spaces) to the volume of solids in a soil mass. It is an indication of how much empty space there is in a soil.

Critical hydraulic gradient: The critical hydraulic gradient, also known as the seepage force, is the slope at which water starts to flow through the soil. It is a measure of the soil's ability to transmit water.

Effect of void ratio on critical hydraulic gradient:

1. Increasing void ratio: When the void ratio of a granular soil increases, it means that there is more empty space between the particles. This increased void ratio leads to a decrease in the soil's ability to transmit water.

2. Decreased soil permeability: As the void ratio increases, the soil becomes less dense and more permeable. This means that water can flow more easily through the soil.

3. Decreased flow resistance: With an increasing void ratio, the flow resistance offered by the soil decreases. This is because there is less contact between the soil particles, allowing water to flow more freely.

4. Lower critical hydraulic gradient: Since the critical hydraulic gradient is a measure of the soil's ability to transmit water, a higher void ratio (indicating more empty space) means that the soil can transmit water more easily. Therefore, the critical hydraulic gradient decreases as the void ratio increases.

Conclusion:

In summary, for a granular soil, the critical hydraulic gradient decreases as the void ratio increases. This is because an increasing void ratio leads to decreased soil permeability and flow resistance, allowing water to flow more easily through the soil.