91Ó°ÊÓ

Effective stress plays a pivotal role in understanding soil mechanics. It's the stress that is actually carried by the soil skeleton. Imagine a sponge filled with water—when you squeeze it, you feel the resistance from the sponge fibers, not the water. That's effective stress.
In soils, effective stress \( \sigma' \) is the difference between the total stress \( \sigma \) and the pore water pressure \( u \). The formula is:

• \( \sigma' = \sigma - u \)

This means that the water trapped in soil pores carries part of the load applied to the soil. The remaining stress is borne by the soil particles themselves. This concept explains why soils behave differently when wet and impacts the soil's strength and stability, an important consideration in designing foundations and other structures.

Saturated soil is a condition where all the pores in the soil are filled with water. Think of a sponge submerged in water—every pore is filled, leaving no air behind.
In engineering, understanding saturated soil is crucial because it affects how the soil will behave under pressure. In this condition, any increase in stress will initially raise the water pressure. This phenomenon is vital in contexts like pavements and dams, where the design must consider how quickly excess water is dissipated. Saturated soil conditions often lead to increased pore water pressures, which can reduce soil stability, especially under loads, because they reduce the effective stress.

Cohesion refers to the component of shear strength in soils that comes from the attraction between particles. It allows the soil particles to stick together and resist being pulled apart.
In terms of calculating shear strength, cohesion \( c' \) is an intrinsic property of fine-grained soils like clays and is measured in units such as kPa. This parameter (\