The ________ of soil is a measure of its resistance to deforming along planes or sliding.

• A. Compressibility
• B. Shear strength
• C. Stiffness
• D. Cohesion

Answer: (B)

The property being tested is how much shear stress soil can resist before it starts to slide along a plane. This is known as shear strength. It represents the soil’s ability to withstand deformation or failure along potential shear surfaces, which is crucial for stability in earthwork and tool movement.

Shear strength comes from two parts: cohesion, the internal attraction between soil particles, and friction, the resistance from particles rubbing against each other when pressed together (described by the internal friction angle). The common relationship is tau = c + sigma' tan(phi), where tau is shear stress, c is cohesion, sigma' is effective normal stress, and phi is the internal friction angle.

Compressibility measures how much volume changes under load, not its resistance to sliding. Stiffness relates to how much a soil deforms under load (its modulus), not the shear resistance. Cohesion is only part of the total shear strength; it doesn’t alone describe resistance to sliding along planes.