RC raft foundation on clay soil

[phuduhudu]

Here in the UK the deemed to satisfy requirements for raft foundations in clay soils near trees require a considerable amount of fill under the raft (about 1m in my case). It also requires a considerable “skirt” of fill material around the raft. The logic is that you are taking the bearing through inert fill down to a depth where the clay is not affected by changes in moisture content due to trees. However, for a small lightweight single storey outbuilding this will negate the benefit of a raft and where the building is near a site boundary it would not be possible to comply with the skirt. It should be possible to design a raft adequately stiff not to require the fill under it. What do others think?

 

[EireChch]

Even if it is infinitely stiff, the swelling pressure of the CLAY could cause tilt settlement in the slab. Especially for a single story light building like yours