Evaluating Behavior of Waffle Mat Foundation on Expansive Soil

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Addis Ababa University


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.



Expansive Soil, Waffle Mat Foundation