California CALTRANS Geotextile Fabrics

Solmax DOT Standard Specification Product Chart (click image to expand)

California CALTRANS - Geotextile Uses

California projects span soft Bay Mud, expansive Central Valley clays, decomposed granite in the Sierra, and fragile coastal bluffs. Add atmospheric-river storms, flash floods after wildfires, and heavy traffic loads, and you get soils that pump, rut, erode, and move fines. Geotextiles are the quiet layer that helps keep roads, bridges, and drainage systems working.

The first role is separation and stabilization. On new lanes, shoulder widenings, and rehab overlays, a woven geotextile is placed between weak native soils and imported base. It stops fines from migrating up into the aggregate under traffic, spreads load, and preserves base thickness—especially useful where construction must proceed over marginal subgrade or where expansive clays swell and soften during winter rains. On very soft ground, crews use the fabric to establish a working platform so haul trucks and pavers don’t punch through

Next is filtration and drainage. Nonwoven geotextiles line underdrain trenches, wrap perforated pipes, and separate drainage aggregate from surrounding soil behind retaining structures and wingwalls. Matching apparent opening size (AOS) and permittivity to the project soils keeps fines in place while letting water move freely—reducing clogged outlets, wet spots, and shoulder failures. In cut slopes and median swales, geotextile helps maintain the gradation of drainage layers so systems keep performing through winter storms.

Where flow concentrates—washes, culverts, outfalls, riverbanks, and coastal works—geotextiles serve as riprap underlayment (rock slope protection). A robust nonwoven filter goes on the prepared subgrade before armor rock. It prevents soil from piping through rock voids during high velocities, wave attack, or debris-laden post-fire floods, helping the rock “lock in” and protecting embankments at bridge abutments, channel bends, and shorelines.

In structures and earth-retaining systems, geotextiles act as joint and face filters. Mechanically stabilized earth (MSE) walls—both precast panel and modular block—use strips of geotextile behind vertical and horizontal joints so backfill fines don’t migrate to the face. The fabric preserves drainage continuity while keeping the fascia clean and preventing loss of material.

California also makes strategic use of pavement interlayers. Asphalt-impregnated nonwoven geotextile placed beneath overlays improves waterproofing and slows reflective cracking—important where daily thermal swings, heavy truck traffic, and oxidizing heat age pavements quickly. On chip seals, paving fabrics can extend service life by limiting water intrusion.

For temporary erosion and sediment control, geotextiles appear in silt fence, inlet protection, curb socks, and check structures. They complement fiber rolls and blankets by filtering flow while trapping fines, which is critical for stormwater compliance in urban corridors and on post-fire slopes. Stabilized construction exits typically include a nonwoven geotextile under coarse rock to distribute wheel loads and limit track-out.

Finally, geotextiles provide liner protection in detention basins, lined ditches, and containment areas. Heavy nonwoven fabrics cushion geomembranes from angular aggregate and construction traffic, reducing puncture risk and extending system life.

Field practice ties it together: prepare subgrades smooth, avoid wrinkles, overlap seams generously, secure with pins or initial lifts, and cover promptly to limit UV exposure. Selection is function-driven—woven for stabilization and tensile strength; nonwoven for filtration, drainage, and protection—tuned to the project’s soils, hydraulics, and traffic demands.

Bottom line: on Caltrans projects, geotextile isn’t “landscape fabric.” It’s a purpose-chosen engineering layer that stabilizes challenging subgrades, controls water and fines during storm events, protects structures and channels, and stretches pavement life across California’s diverse and demanding conditions.

California CALTRANS