Failure occurring when soil or subgrade beneath a foundation cannot safely transmit applied loads to deeper strata, producing either shear rupture of the supporting soil (ultimate bearing failure) or excessive settlement that violates serviceability limits.

Principle

Bearing failure arises when applied contact stresses exceed the soil's ultimate bearing resistance or when compressibility and pore-pressure response produce settlement beyond acceptable tolerances; both shear capacity and settlement performance must be evaluated because safe shear strength does not guarantee acceptable settlements.

Demonstration

Illustrative scenario → A shallow column footing is placed on a high-plasticity clay. Under sustained loading the footing settles progressively beyond allowable limits while no visible shear plane forms. Engineers recognize serviceability bearing failure, increase foundation area, or replace the soil with stiffer material to reduce settlement.

Misapplication

Interpreting any observed settlement as bearing-capacity failure. The semantic error is conflating serviceability settlement due to long-term consolidation or construction sequence with ultimate shear rupture; correct analysis distinguishes mechanisms by instrumentation, load tests, and profile investigation.

Consequence

Bearing failure can produce differential settlement, tilting, cracking of superstructure and loss of function. Ultimate shear rupture may be sudden and lead to collapse of supported elements; excessive settlement may be gradual but still cause functional failure and expensive remediation.

Reversal

At shallow scales and under spreading loads, apparent bearing failure may instead be local structural failure (e.g., slab punching or inadequate footing design) or global instability (slope failure) rather than subgrade shear rupture; conversely, deep foundations may transfer loads to competent layers so bearing failure is not governing.

Boundary

Clearly within: a shallow spread footing on weak compressible soil exhibiting shear rupture or intolerable settlement under design loads. Boundary case: a rigid mat foundation where settlement is distributed — classification depends on acceptable differential and total settlements. Clearly outside: pile-supported foundations where load is carried by shaft and end-bearing to competent strata rather than by shallow bearing capacity.

Semantic Tension

Ultimate bearing capacity (safety) ↔ Serviceability settlement (function); design must balance preventing shear rupture with limiting settlements acceptable for use and durability, often requiring different remedies.

Synthesis

Effective foundation design requires parallel assessment of shear capacity and settlement behavior; preventing collapse (capacity) and preventing unacceptable deformation (serviceability) are distinct objectives that both govern foundation choice and remediation.