Model#4 This model parameterises the effect of soil shear deformation on overall foundation stiffness through a concept known as “co-operative width” as introduced by Walsh and Cameron. Unfortunately, there have been some recent reports of damages to hundreds of houses supported by waffle slabs (designed to AS2870) on highly reactive soils of Western suburbs of Melbourne, Victoria, Australia. Reactive soil can swell/shrink with changes in moisture content, and this could happen due to several reasons, including: (1) seasonal/natural causes, such as rain, evaporation, and effect of adjacent trees and (2) other causes, such as pipe leakage, poor or faulty drainage systems, and poor surface water management during and after construction.In Australia, AS2870-2011 is the relevant standard for analysis, design and construction of residential slabs and footings.

In Australia, waffle rafts are commonly constructed to support relatively light residential structures (houses).Slabs are primarily designed to limit the differential movement of the structure considering the gravity loads that need to be safely transferred to ground and also the potential movements of underneath reactive soil. Raft foundations (waffle raft/stiffened raft with or without deep edge beam) are commonly used, in a number of places around the world, as the preferred foundation system for supporting structures. The analyses also suggest that predefining a critical scenario and disregarding the history of loading is not necessarily conservative. It is found that the conventional assumption of a constant soft soil stiffness coupled with a stepped transition to that of hard soil is generally unconservative.

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