A property owner elected to construct an office and apartment building in a very small infill space in a historical Colorado Springs Neighborhood. Because the lot was located between two established businesses, there was very limited room for the use of heavy construction equipment. A new approach was needed that would eliminate the need to over excavate the bad soil and import structural fill.
The only realistic option was to construct a structurally suspended floor system, supported on a grid of piers. However, the construction methods used for “typical” structurally suspended floors still require at least 18″- 24″ of excavation.
As a result, the owner decided to use the Tella Firma™ foundation system because it requires virtually no excavation. With Tella Firma™, the slab is simply built on top of the existing ground and then raised, creating the necessary void between the soil and the foundation.
Tella Firma™ is a patented process for constructing a new type of Structurally Suspended concrete foundation system. With this system, the slab is poured directly on top of the existing ground, after first installing a grid of piers or pads. In this case, helical piers were used.
After the concrete cures to the proper strength (typically 3 days), the post-tensioned cables are pulled, and the slab is raised to the desired height. This process utilizes mechanical screw jacks embedded in the slab, directly over each pier. Therefore, all the structural loads of the home are distributed to the piers which in turn distribute them to the stable soils below.
The slab is raised 6″ – 10″ above the ground, based on the recommendations of the Geotechnical engineer. The resultant void between the ground and the foundation serves to isolate the slab from any future soil movement. The problem soils may then move up or down in the future without affecting or even touching the floor.