Using Wafflemat with Ribbed Slab foundations can provide a much more rigid and better performing foundation on expansive soil. Warranty repair costs caused by expansive soil are virtually eliminated and construction costs can be reduced. For example, instead of removing a thick layer of expansive soil or chemically modifying the expansive soil, which are solutions often recommended by geotechnical engineers, and both of which are costly, the Ribbed Slab foundation can be designed as a hybrid system with Wafflemat used to create voids under the slab and between the deep beams. The soil can expand in to the voids created by Wafflemat. This minimizes the uplift of foundations and the resultant damage to the house structure.
Depending on the expansion potential of the soil, this type of foundation is usually placed on imported non-expansive fill or directly on the existing expansive soil. When Wafflemat is integrated into the Ribbed Slab design; the foundation now has the ability to absorb expanding soil. The floor slab with Wafflemat is also much more rigid than the thin floor slab used in a Ribbed Slab.
Without Wafflemat, the thin floor slab in the Ribbed Slab foundation is in full contact with the soil. When the soil expands, it pushes against the underside of the thin floor slab. Note that the use of non-expansive fill is usually specified by geotechnical engineers to reduce the amount of potential vertical rise of underlying expansive soil.
Non-expansive fill does not eliminate the effect of any remaining underlying expansive soil under foundations—it transmits the expansive soil forces upward. The expansion potential of expansive soil is usually only eliminated if all the underlying expansive soil is removed and replaced. This can be a very expensive option.
Ribbed Slab Foundation Ribbed Slab Foundation With Wafflemat Design For Low To Medium Expansion Soil Ribbed Slab Foundation With Wafflemat Design For High To Very High Expansion Soil (Note Deeper In-Ground Beams):
Using Wafflemat With Ribbed Slab
|With Wafflemat:||Without Wafflemat:|
|Foundation absorbs volume |
change of expansive soil, thereby reducing uplift forces
|Expansive soil pushes the
|Much more rigid floor slab||Thin flexible floor slab, more easily subject to cracking
|Non-expansive fill is usually |
|Non-expansive fill is used to
attempt to reduce uplift forces
of expansive soil