Municipal Road Soft Soil Subgrade (Staple Fiber Needle-Punched Nonwoven Geotextile)
Municipal Road Soft Soil Subgrade (Staple Fiber Needle-Punched Nonwoven Geotextile)
1. Project Background
This is an urban feeder road. The site is covered by 3.0–4.5 m thick muddy soft soil at the surface, featuring low bearing capacity and high compressibility. If crushed stone is backfilled directly, the stone will penetrate into the soft soil while fine soil particles migrate upward, clogging the cushion and resulting in differential settlement and pavement cracking at a later stage. A combined treatment scheme of “prefabricated vertical drain board + geotextile + crushed stone cushion” is adopted.
2. Geotextile Specification & Consumption
Type: Staple fiber needle-punched nonwoven geotextile
Specification: 200 g/m²; longitudinal tensile strength ≥8.0 kN/m; equivalent opening size O₉₅ ≤0.08 mm; vertical permeability coefficient ≥1×10⁻³ cm/s
Laying area: 12,600 m²; wastage factor: 8%; procurement quantity: 13,608 m²
3. Functions & Performance of Geotextile
✅ Separation + Filtration + Drainage
Separation: Prevent intermixing between the crushed stone cushion and underlying soft soil, and protect the cushion voids from being blocked by fine particles.
Filtration: Allow free discharge of pore water while retaining soil particles to prevent piping.
In-plane drainage: Collect seepage water from the soft foundation and divert it to the side blind ditches.
✅ Performance outcome: The voids of the crushed stone cushion remain unclogged in the long run; the subgrade settlement rate is greatly reduced. No pavement pumping or cracking has occurred after two years of traffic opening.
4. Construction Parameters
Laying method: Manual rolling laying; mechanical dragging is prohibited. Relaxation allowance: 1%–2%.
Overlap: Longitudinal overlap ≥20 cm; overlap on slope sections ≥30 cm. The upper sheet overlaps the lower sheet, following the direction of filler placement.
Fixation: U-shaped geotextile nails (spacing: 1.5 m) plus sandbag weighting at edges. Heavy compaction directly on the geotextile surface is not allowed.
Protective cover: The first layer of crushed stone backfill shall be completed within 48 hours after geotextile laying; backfill shall proceed from the centre towards both sides.
5. Division of Work with Other Measures
Prefabricated vertical drain boards: Vertical drainage passages to transfer pore water from deep soft soil up to the geotextile layer.
Geotextile: Horizontal filtration and separation layer, receiving outflow from drain boards and separating soft soil from crushed stone.
Crushed stone cushion: Load-bearing layer and transverse water conveyance channel.
Surcharge preloading: Apply additional stress on soil to accelerate consolidation of soft soil.
