Montana MDT Geotextile Fabrics

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

Montana MDT - Geotextile Uses

Montana’s highways traverse glacial tills, windblown silts, alluvial gravels, and weathered bedrock across valleys and steep mountain corridors. Add long freeze–thaw seasons, deep frost, rain-on-snow events, spring runoff, wildfire burn scars that shed debris, and heavy truck traffic, and you get subgrades that can soften, pump fines, rut, scour, and settle. Geotextiles are the quiet engineering layer that helps pavements, structures, and drainage systems keep performing through it all.

Separation and stabilization. On new lanes, shoulder widenings, and staged construction over marginal subgrade, a woven geotextile goes between native soil and granular base. It blocks fine soils—especially silts and clayey tills—from migrating up into the aggregate under traffic, spreads load, and preserves base thickness. Where subgrades are very soft or seasonally saturated (valley bottoms, utility trench crossings, wet shoulders), crews first roll out fabric to create a working platform so haul trucks and pavers don’t punch through. On exceptionally weak ground, geotextile is often paired with geogrid for added stiffness and faster production.

Filtration and drainage. Water drives many failures in Montana. Nonwoven geotextiles line underdrain and edge-drain trenches, wrap perforated pipe, and separate drainage stone from surrounding soils behind retaining walls, abutments, and wingwalls. Correct apparent opening size (AOS) and permittivity let water move while fines stay put, reducing clogged outlets, wet spots, and shoulder drop-offs. In cold regions, placing a nonwoven over open-graded aggregate creates a capillary break, limiting upward moisture that fuels frost heave and weakens base layers in winter.

Riprap underlayment and scour control. Where flows concentrate—culverts, storm outfalls, river bends, and mountain channel linings—geotextiles serve as underlayment beneath riprap or rock armor. A robust nonwoven filter is placed on the prepared slope or bed before stone. It prevents the subgrade from piping through rock voids during high velocities, ice-out, snowmelt torrents, and debris-laden post-fire floods, helping the rock “lock in” and protecting embankments at bridge approaches and channel transitions. On steep slopes or fluctuating water levels, seams are overlapped generously or sewn and anchored to stay continuous under shifting hydraulics.

Structures and MSE walls. MDT corridors include many mechanically stabilized earth (MSE) walls and grade separations. Geotextiles act as joint and face filters, tucked behind panel or block joints so backfill fines don’t migrate to the face while drainage continuity is preserved. The same idea applies at wingwalls, backwalls, and structural penetrations, where a filter layer keeps weeps functioning without trapping water.

Pavement interlayers. Asphalt-impregnated nonwoven geotextile beneath overlays improves waterproofing and slows reflective cracking—valuable where large daily temperature swings, studded tires, and deicing chemicals accelerate pavement aging. On chip seals common to rural routes, paving fabrics limit water intrusion into base and subgrade, extending service life with minimal added thickness.

Temporary erosion and sediment control. Geotextiles appear in silt fence, inlet protection, curb socks, and check dams. They filter runoff while trapping fines—critical for stormwater compliance on steep cuts, long medians, and wildfire recovery sites. At project entrances, stabilized construction exits typically include a nonwoven geotextile under coarse rock; the fabric spreads wheel loads and prevents stone from punching into wet soils, reducing track-out onto public roads.

Liner protection and containment. Heavy nonwoven geotextiles cushion geomembranes in stormwater basins, lined ditches, salt-shed pads, and deicing-brine containment, protecting liners from puncture by angular aggregate and construction traffic.

Field practice. Performance hinges on basics: prepare subgrades smooth, avoid wrinkles, overlap or sew seams as required, anchor with pins or the first lift, and cover promptly—especially at elevation, where UV exposure is intense. Selection is function-driven—woven for stabilization and tensile capacity; nonwoven for filtration, drainage, and protection—tuned to Montana’s soils, hydraulics, and traffic demands.

Bottom line: on MDT projects, geotextile isn’t “landscape fabric.” It’s a purpose-chosen engineering layer that stabilizes soft ground, controls water and fines through harsh seasons, protects structures and channels, and stretches pavement life statewide.

Montana MDT