Factor of Safety for Soil Bearing Capacity

Factor of Safety for Soil Bearing Capacity

To find out the safe bearing capacity for any type of soil we must needed factor of safety. The value of FOS for bearing capacity differs by the soil type and condition, method of exploration, level of uncertainty in soil, importance of structure and consequences of failure, and design load occurrence.        This factor is helpful to find out the allowable bearing capacity. It is used to design the footing. Mostly used FOS as 3 for any type of footing. It may be reduced for raft or mat footing. It may be increased for isolated spread footings. Category Typical structures Characteristics of the category Design factor of safety – – – Thorough and complete soil exploration Limited soil exploration I Railway bridges, ware houses, blast furnaces, hydraulic, retaining walls, silos Maximum design load likely to occur often, consequences of failure – disastrous 3.0 4.0 II Highway bridges, light industrial and public buildings Maximum design loads may occur occasionally, consequence of failure – serious 2.5 3.5 III Apartment and office buildings Maximum design load unlikely to occur 2.0 3.0         Bearing capacity is the major factor influencing in structural stability and settlement. So we cannot take much risk in allowable bearing capacity that’s why we use higher percentage/value of factor of safety compare to other structural elements like Beam, Slab, Coolum, etc…