Structural Engineer – Improve Slab on Grade Foundation Performance

CRACKED BRICKExpansive Clays.  Can’t live with them.  Can’t live without them.
If you live in the San Antonio or Austin areas, you know the havoc these soils can wreak on a slab on grade foundation system.  But do you know how simple it is to prevent clay soil slab damage while at the same time improving its performance potential?
To help reduce the potential of future concrete foundation distress and residence interior/exterior brittle material cracking occurrences, a homeowner should consider implementing the following non-structural maintenance/code compliance guidance:
  1. If plumbing (pool, sub-foundation supply or drain system) leaks are suspected, or if previous plumbing tests did not comprehensively test all drain and supply lines underneath the foundation, test the house plumbing (supply and drain) and any yard irrigation systems (or connected hose bibbs and water supply piping) to assure their water tightness. Water accumulation beneath the foundation system can cause a localized and potentially damaging upward displacement of the foundation surface.
  2. Consider saw-cutting & filling concrete floor surface cracks with a low viscosity epoxy resin compound to help prevent their potential increase in length, wide, depth over time;
  3. Consider installing (new) or connecting (existing) gutter/downspout systems to an underground drain system (refer to “Surface Water Drainage, Option A) if available to ease the capture, collection, and draining of roof storm water away from the foundation perimeter and to:  help prevent ground surface erosion or scouring;  help prevent foundation bearing soil supersaturation (refer to next bullet);  help prevent acute water ponding in areas on or about the foundation perimeter.
  4. Maintain a uniform soil moisture content along and about the foundation system perimeter where it is reasonable to do so.  Guidelines (a.) and (b.) below may be followed:   (a)  Excessively wet foundation bearing soils can allow the foundation system to displace vertically downward over time. Assure soils near the foundation perimeter do not become excessively saturated (keep soil moisture on the low end of its plastic range).  (b) Excessively dry bearing soils and subgrade material can shrink volumetrically, allowing abnormal vertical displacement or angular rotation of the slab-on-grade foundation system. To help reduce excessive foundation planar tilting resulting from soil drying and shrinking along its perimeter, assure plenty of ground surface vegetative cover (landscaping) flourishes near its perimeter while maintaining uniform beam bearing soil moisture contents (irrigate yard regularly, but not excessively while keeping soil moisture on the low-end of its plastic range).
  5. The Post Tensioning Institute Publication “Design and Construction of Post Tensioned Slabs-on-Ground” states: Assure any air conditioning condensate discharge line directs condensate away from the foundation system to prevent excessive water from saturating the foundation bearing soils as applicable.
  6. Watering should be done in a uniform, systematic way as equally as possible on all sides of the foundation to keep the soil moist. Areas of the soil that do not have ground cover may need more moisture as they are more susceptible to evaporation.
  7. During extreme hot & dry periods, close observations should be made around foundations to insure that adequate watering is being provided to keep soil from separating or pulling back from the foundation.
  8. Assure any water heater TPRV discharge lines direct condensate away from the foundation system to prevent excessive water from saturating the foundation bearing soils.
  9. Attempting to replace expected local climate precipitation by artificially imbibing moisture into the foundation bearing soils with appliances (example: soaker hose or irrigation system) may negatively impact the structural efficacy the foundation system. No known authoritative treatise or code based protocols exist which offer approved instructions for their safe, hazard free, long-term use.