Define the concept of soil bearing capacity failure modes: general shear, local shear, and punching shear.

• A. Tensile and compressive only.
• B. Frictional slip and tunnel formation.
• C. Hydrostatic pressure.
• D. General shear, local shear, and punching shear.

Answer: (D)

Understanding how soil fails under bearing loads involves recognizing three classic patterns: general shear, local shear, and punching shear. General shear failure occurs when the footing induces a wide shear zone that propagates through the soil, creating a wedge-shaped failure surface and leading to rapid, large settlements and loss of overall stability. Local shear failure is more confined, with a shallow shear zone near the footing edge that doesn’t extend through the entire depth, resulting in smaller, more localized deformations. Punching shear happens under concentrated loads (often circular footings), where the soil under the load is shoved downward in a column-like plug, producing a vertical, center-out failure around the footing with little global tilting.

These three patterns capture the main ways soils typically fail in bearing scenarios, depending on footing size and shape, soil strength, and load distribution. Other phenomena like hydrostatic pressure or frictional slip don’t represent the primary bearing-capacity failure modes.