Effective stress on soil A. Increases voids ratio and decreases permeability B. Increases both voids ratio and permeability C. Decreases both voids ratio and permeability D. Decreases voids ratio and increases permeability

The correct answer is: C. Decreases both voids ratio and permeability.

Effective stress is the stress that acts on the soil particles and is responsible for the strength of the soil. It is calculated by subtracting the pore water pressure from the total stress.

The voids ratio is the ratio of the volume of voids to the volume of soil solids. It is a measure of the looseness or compactness of the soil.

The permeability is the ability of the soil to transmit water. It is a measure of the size and interconnectedness of the pores in the soil.

When effective stress increases, the soil particles are forced closer together. This decreases the voids ratio and the permeability of the soil.

The following are the explanations for each option:

• Option A: Increases voids ratio and decreases permeability. This is incorrect because effective stress decreases the voids ratio.
• Option B: Increases both voids ratio and permeability. This is incorrect because effective stress decreases both the voids ratio and the permeability.
• Option C: Decreases both voids ratio and permeability. This is correct because effective stress decreases both the voids ratio and the permeability.
• Option D: Decreases voids ratio and increases permeability. This is incorrect because effective stress decreases the voids ratio and the permeability.