Evaluating Behavior of Waffle Mat Foundation on Expansive Soil
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Date
2019-10
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Addis Ababa University
Abstract
In Ethiopia, expansive soils are found in wide areas. Those soils cause significant damage to
structures
built on them.
Particularly
lightly
loaded
building with
different
foundation
types such as isolated and mat foundations. Are more prone to damage there is a
general increase in building construction with increasing population at a very faster rate
and large coverage of expansive soil. Therefore there is need to understand the characteristics
of
these
soil
type
and
appropriate
foundation
types.
The focus of this thesis is to evaluate the factors for moisture distribution with depth of
soil, edge moisture distance and amount of soil heave by using proposed formula by
Remon I. Abdelmalak (2007), the formula depends on pioneer work of Mitchell (1979).
For the determination of deflection, moment and shear of waffle mat foundation assumed
as interconnected T-beam. For soil heave the beam to assumed as simply supported and
design as beam on elastic foundation using formula by M. Hetenyi (1946) to determine
subgrade reaction of the soil. When soil shrinks the beam has no contact with soil and
assumed as cantilever beam by using beam formula.
Diffusivity coefficient has great sensitivity to moisture distribution with depth, edge
moisture distance and soil heave. It has more than 100% increasing effect for moisture
distribution with depth, edge moisture distance and soil heave when the soil goes from
uncracked condition to crack. Change of surface edge suction has secondary sensitivity.
Drying period has little effect on the swelling characteristics of expansive soil. Differential
soil
heave
and
edge
moisture
distance
increase
when the
slab
dimension
increase.
Beam depth has great sensitivity to deflection of the T-beam for dry soils. The deflection
of the beam reduce by 75.6% when the beam depth increases two fold. Flange thickness
has secondary sensitivity to deflection and flange width has small effect. For soil heave
beam width has great sensitivity to deflection. Increases contact area and swelling pressure
when
the
beam
width
increases.
But
other
parameters
have
almost
constant
sensitivity
for
deflection.
Waffle mat foundation has reduced construction cost and time comparing with isolated
footing. It has also high stiffness. Waffle mat foundation is a better foundation alternative
for
light
loaded
structure on
expansive
soil.
Description
Keywords
Expansive Soil, Waffle Mat Foundation