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Ground Stability, Foundations and Substructures 95
Existing wall of
adjoining building
Columns
Asymmetrical
combined base
foundation
Figure 3.27 Asymmetrical combined base foundation.
Lightly loaded
column
Boundary
of site
Heavily loaded
column
Heavily loaded
column
Boundary
of site
Lightly
loaded
column
Beams
Equal Equal
Centre of
gravity
(a)
Combined foundation
Centre of
gravity
(b)
Trapezoidal combined
foundation
Figure 3.28 (a) Rectangular combined base foundation. (b) Trapezoidal combined base
foundation.
Where the subsoil under the wall of an adjoining building is comparatively sound and
the load on columns next to the existing wall is moderate, it may be acceptable to use an
asymmetrical combined base foundation such as that illustrated in Figure 3.27. Some of
the load on the column base, next to the existing wall, will be transferred to the wider part
of the reinforced concrete combined base to reduce the surcharge of load on the foundation
of the existing wall. Where the boundary of a site limits the spread of the bases of columns
next to the boundary line, a system of rectangular or trapezoidal combined reinforced
concrete bases may be used.
A rectangular, combined base is used where the columns next to the boundary are less
heavily loaded than those distant from the boundary, as illustrated in Figure 3.28a. The
load from heavily loaded columns next to the boundary can be more widely spread than