FACTOR OF SAFETY FOR
BEARING CAPACITY OF SOILS
Bearing capacity of soils are reduced by a factor called factor of Safety to underestimate the bearing capacity of soils. This value of factor of safety depends on following factors:
1. Type of soil
2. Method of exploration
3. Level of Uncertainty in Soil Strength
4. Importance of structure and consequences of failure
5. Likelihood of design load occurrence, etc.
Generally a factor of safety F = 3 is assumed for bearing capacity calculations, unless otherwise specified for bearing capacity problems. Table-1 gives the details of factors of safety to be used under different circumstances.
Fig: Effect of Bearing Capacity of Soil on Foundation
Table-1: Typical factors of safety for bearing capacity calculation in different situations
| Category | Typicalstructures | Characteristics of the category | Design factor of safety | |
| Thorough and completesoil exploration | Limited soil exploration | |||
| A | Railway bridges, warehouses, blast furnaces, hydraulic, retaining walls, silos | Maximum design load likely to occur often,
consequences of failure – disastrous |
3.0 | 4.0 |
| B | Highway bridges, light industrial and public buildings | Maximum design loads may occur occasionally,
consequence of failure – serious |
2.5 | 3.5 |
| C | Apartment and office buildings | Maximum design load unlikely to occur | 2.0 | 3.0 |
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