Short answer
Shrink-swell is how much a soil swells when wet and shrinks when dry. USDA classes it by linear extensibility: under 3% low, 3 to 6% moderate, 6 to 9% high. Our USDA sampling found Woodlake’s soils mostly high, Exeter, Lindsay and parts of Tulare moderate, and Visalia and Hanford low.
Key facts
- Shrink-swell classes: under 3% low, 3 to 6% moderate, 6 to 9% high, over 9% very high (USDA NRCS California)
- Above 3%, shrinking and swelling can damage buildings, roads and other structures (USDA NRCS California)
- Woodlake: San Joaquin soils (58% of sampled ground) rated high (USDA soil survey)
- Visalia and Hanford: every major sampled soil rated low (USDA soil survey)
Town by town
We sampled 25 points in each city with USDA’s Soil Data Access and weighted each soil by its share of the map unit. The table shows the main soils.
| Town | Main soil | Shrink-swell by soil | Corrosion of concrete (main soil) |
|---|---|---|---|
| Exeter | Flamen (96%) | Flamen moderate, Exeter moderate | Low |
| Visalia | Tagus (48%) | Tagus low, Nord low, Grangeville low, Akers low | Low |
| Tulare | Colpien (52%) | Colpien moderate, Nord low, Flamen moderate, Yettem low | Moderate |
| Lindsay | Exeter (91%) | Exeter moderate, Greenfield low | Low |
| Woodlake | San Joaquin (58%) | San Joaquin high, San Emigdio low, Seville high, Porterville high | Low |
| Hanford | Nord (79%) | Nord low, Wasco low | Low |
| Lemoore | Grangeville (38%) | Grangeville low, Nord low, Lakeside moderate, Lemoore low | High |
What the rating means
USDA’s California engineering interpretations define linear extensibility as the change in length of a soil clod as it dries from moist to dry. Under 3% is low shrink-swell, 3 to 6% moderate, 6 to 9% high and over 9% very high. Above 3%, USDA says shrinking and swelling can damage buildings, roads and other structures.
What it means for a slab
NRMCA’s cracking guide starts with the ground: remove topsoil and soft spots, compact the subgrade, and slope it for drainage. On swelling soils, steady moisture matters too, which is why drainage away from the slab is worth asking about. Foundation design on any lot comes from the plans and the local permit.
From Tim’s jobs
