Which of the following properties depend on effective stress?

Explanation:

• Effective stress controls the shear strength of soil by determining the resistance offered by soil particles to sliding. As effective stress increases, the interparticle contact force increases, improving the soil’s ability to resist shear. This relationship is defined by the Mohr-Coulomb strength criterion.
• Compressibility of soil is directly influenced by effective stress, as it governs how much the soil consolidates under load. When effective stress increases, voids between soil particles decrease, leading to settlement. This is particularly important in clayey soils under long-term loading.
• Permeability is indirectly affected by effective stress, especially in fine-grained soils. As effective stress increases, the soil becomes denser, reducing the size of pore spaces. Smaller pore spaces lower the rate at which water can flow through the soil.
• Volume changes in soils under loading or unloading are dependent on changes in effective stress. Higher effective stress compresses the soil, while a decrease can lead to expansion or swelling. This behavior must be considered in foundation and earthwork designs.
• In saturated conditions, total stress is divided between pore water pressure and effective stress. Only the effective portion contributes to soil stiffness and strength. Understanding this is critical in analyzing submerged or water-logged soils.
• All essential soil behavior—strength, settlement, and permeability—is governed by effective stress rather than total stress. Engineers rely on effective stress to predict soil response under different loading conditions. It is the central concept in soil mechanics.

Additional InformationShear Strength

• Shear strength depends directly on effective stress because only the soil grains (not pore water) resist shearing. As effective stress increases, the soil structure becomes more stable and resistant to failure.

• In saturated soils, a rise in pore water pressure reduces effective stress, leading to a decrease in shear strength, which is critical in slope failures and bearing capacity analysis.

Compressibility

• Compressibility refers to the reduction in soil volume under applied stress and is controlled by effective stress. When effective stress increases, soil particles are pressed closer together, reducing voids and causing settlement.

• In fine-grained soils like clay, compressibility is high and time-dependent due to low permeability, which delays drainage and extends consolidation time.

Permeability

• Permeability is affected indirectly by effective stress, as higher effective stress compacts the soil, reducing pore size and thus the ease of water flow.

• This effect is more prominent in cohesive soils, where small changes in structure from increased effective stress can significantly reduce permeability.