February 24, 2025 · Foundations
Understanding Central Texas Soil
Blackland prairie soils contain high percentages of montmorillonite clay that can swell 10-15% when wet and shrink dramatically when dry — strong enough to crack concrete and shift structures.
Geotechnical Investigation
Before designing a foundation, a geotech engineer tests soil samples. The Plasticity Index (PI) measures movement potential. The report recommends foundation depth, reinforcement, and special preparation.
Design Strategies
Deeper grade beams resist bending from differential movement. Post-tension compresses the slab against cracking. Void boxes allow soil to swell without lifting the structure. Moisture barriers reduce the variation that drives expansion.
Drainage Importance
Maintain consistent moisture around your foundation. Gutters should direct water 5+ feet away. Grade should slope away at minimum 5% for 10 feet. Foundation soaker hoses help during dry spells.
When to Worry
Cracks wider than 1/8 inch, sticking doors/windows, or visible gaps between walls and ceilings may indicate movement requiring evaluation.