Some areas in Texas have deep expansive soil that will often require the use of a deep foundation design using drilled concrete piers, with concrete grade beams interconnecting the tops of the piers, with a flat slab on grade tied to the tops of the grade beams, and with replacement of some of the underlying expansive soil to reduce the potential vertical rise of the expansive soil. The result of this design is that the upward forces of soil expansion are still transmitted directly to the grade beams and the undersides of the thin floor slab. Many foundation design engineers elect to not tie the grade beams to the tops of the piers, thereby allowing the entire slab foundation and grade beams to lift off the tops of the piers when expansive soil pushes upward. The piers act only as a downward stop for the grade beams when the expansive soil dries and recedes vertically.
Using Wafflemat with this foundation design provides voids in the slab for absorption of some of the volume change of expanding soil. The more closely spaced beams of the Wafflemat foundation also provide a much more rigid slab between grade beams than the thin floor slab that is commonly used. Bending of the slab due to expansive soil is greatly reduced, thereby minimizing damage to the structure.
Structural Slab on Piers:
Wafflemat with Structural Slab on Piers:
What happens when you use Wafflemat with Structural Slab on Piers?
- Wafflemat absorbs some of the volume change of expansive soil, thereby reducing uplift forces and vertical movement.
- Wafflemat creates a more rigid floor slab.
- Non-expansive fill is usually not required.
And without Wafflemat?
- Expansive soil is in full contact with the foundation grade beams and slab and pushes them upward.
- The thin flexible floor slab between grade beams is more easily subject to bending and cracking.
- Non-expansive fill is often used to attempt to reduce uplift forces of expansive soil.