Civil Engineering Reference
In-Depth Information
Chapter 9
Bearing Capacity and
Shallow Foundations
9.1 Bearing capacity terms
The following terms are used in bearing capacity problems.
Ultimate bearing capacity
The value of the average contact pressure between the foundation and the soil which will produce shear
failure in the soil.
Safe bearing capacity
The maximum value of contact pressure to which the soil can be subjected without risk of shear failure.
This is based solely on the strength of the soil and is simply the ultimate bearing capacity divided by a
suitable factor of safety.
Allowable bearing pressure
The maximum allowable net loading intensity on the soil allowing for both shear and settlement effects.
9.2 Types of foundation
Strip foundation
Often termed a
continuous footing
this foundation has a length significantly greater than its width. It is
generally used to support a series of columns or a wall.
Pad footing
Generally an individual foundation designed to carry a single column load although there are occasions
when a pad foundation supports two or more columns.
Raft foundation
This is a generic term for all types of foundations that cover large areas. A raft foundation is also called
a
mat foundation
and can vary from a fascine mattress supporting a farm road to a large reinforced con-
crete basement supporting a high rise block.
