Explain the concept of ultimate bearing capacity and name two factors that influence it.

• A. It is the maximum soil pressure that can cause shear failure under a footing; factors include groundwater presence and footing size/depth.
• B. It is the maximum load a footing can carry before excessive settlement; factors include soil moisture and temperature.
• C. It is the resilient modulus of soil under cyclic loading; factors include loading frequency and soil density.
• D. It is the pressure at which soil yields in compression; factors include grain size and mineralogy.

Answer: (A)

The main idea here is ultimate bearing capacity: it is the maximum vertical soil pressure that can be transmitted through a footing to the soil before failure occurs by shear. This limit is reached when the soil’s shear strength can no longer resist the imposed load, so the foundation can no longer carry the load safely.

Two factors that influence this limit are groundwater presence and the footing’s size and depth. Groundwater affects ultimate capacity through pore water pressures. When a water table is present or the soil is saturated, pore pressures rise under loading, reducing the effective stress that actually mobilizes shear strength. Less effective stress means lower shear resistance, so the ultimate bearing capacity decreases.

Footing size and depth change how the load is distributed and how much overburden stress exists at the base. A wider footing alters the stress field and broadens the potential shear zone, modifying the capacity terms that depend on footing width. Greater depth increases the overburden pressure at the base, elevating the contribution of the overburden term to the ultimate capacity, though it also brings practical concerns like settlement. Together, these factors can appreciably change the maximum load the soil can carry before failure.

Other concepts mentioned in the other options describe different soil responses (like settlement criteria, dynamic/modulus behavior, or material yield characteristics) rather than the ultimate load at which shear failure occurs under a footing.