Allowable bearing capacity of shallow foundations In geotechnical engineering practice, the permissible (allowable) bearing capacity of a foundation is governed by two independent criteria. Identify the correct pair of criteria that must both be satisfied for safe and serviceable performance.

Introduction:
Designing the allowable bearing capacity of a shallow foundation requires attention to both ultimate limit states and serviceability limit states. The soil–foundation system must not reach a shear (bearing) failure under factored or working loads, and at the same time, the settlement under service loads must remain within tolerable limits to protect the superstructure from damage and functional impairment.

Given Data / Assumptions:

• Shallow foundation on natural soil or engineered fill.
• Working (service) load cases considered for settlement; ultimate resistance considered for shear/bearing.
• Allowable bearing pressure is derived by applying factors of safety and/or serviceability checks.

Concept / Approach:

The classic bearing capacity problem addresses two distinct checks. First, shear failure (general or local) must not occur in the soil beneath the foundation. Second, settlements (both total and differential) must be within permissible limits for the supported structure. The allowable bearing capacity is often the lesser pressure arising from these two checks: one from dividing ultimate capacity by a factor of safety, the other from settlement analysis and permissible limits (e.g., 25 mm to 75 mm depending on structure type).

Step-by-Step Solution:

Verification / Alternative check:

Back-analyses of case histories show structures that meet shear safety can still suffer distress from excessive settlement. Conversely, a very stiff soil may pass settlement criteria while shear governs at lower pressure. Hence both checks are necessary and complementary.

Why Other Options Are Wrong:

Options A and B include ‘‘tensile failure’’ which is not a conventional criterion for soil bearing capacity. Option C mentions ‘‘bond failure’’ which is not relevant to soil–foundation interface at footing levels. Option E pertains to hydraulic or uplift scenarios, not the general bearing capacity criteria.

Common Pitfalls:

Using only a factor of safety on ultimate capacity and ignoring settlement; neglecting differential settlement between supports; relying on undrained parameters for long-term settlement predictions where drained behavior controls.

Final Answer:

shear failure and settlement