Comparison of Raft and Folded Plate Foundations

The design of raft depends on several factors like the stiffness of
superstructure and foundation, bearing capacity or modulus of subgrade
reaction of the soil, column spacing, projection of raft beyond the outer lines
of boundary columns and the material strengths used in construction. For a
given arrangement of superstructure, soil strength is the most important factor
affecting the design and cost of construction of a raft. Folding of a raft or
folded plate foundations can be used effectively to reduce the material
consumption in a raft construction. A raft folded in straight lines is easy to
construct and it increases the stiffness of the foundation, which in turn reduces
the total and differential settlements of the structure as a whole. The present
study compares the performance of raft and folded plate foundation. The
advantages of folding the raft on the structural design of foundation and
superstructure are highlighted. The initial designs were prepared using
Winkler method and the impact of varying the coefficient of subgrade reaction
on the design of raft and folded plate foundations were compared. Then
continuum method was used for representing soil and its properties were
varied in line with the variation in coefficient of subgrade reaction. The impact
of this modeling and variation in soil properties on the foundation and super
structure design were also compared. In addition the effect of increase in
projections to the raft beyond the outer lines of boundary columns are also
presented.