Earth-Rock Cofferdam of Water Control Hub, Hydraulic Filtration Project (Staple Fiber Non-woven Geotextile)
Earth-Rock Cofferdam of Water Control Hub, Hydraulic Filtration Project (Staple Fiber Non-woven Geotextile)
1. Project Background
This earth-rock cofferdam supports the sluice, ship lock and power station of a water control hub. The cofferdam retains water, and its embankment is composed of silty fine sand with high risk of seepage deformation, prone to piping and soil flow. Geotextile filter layers are laid in a large area on the upstream face of the cofferdam, drainage prism and drainage channels behind the dam, with a total consumption of approximately 900,000 m².
2. Geotextile Specification & Consumption
Type: Staple fiber needle-punched non-woven geotextile
Specification: 300 g/m². Its equivalent opening size O₉₅ matches the gradation of silty fine sand of the embankment, and the vertical permeability coefficient is higher than that of the embankment soil, realizing soil retention and water permeability.
Net laying area: 900,000 m²; wastage factor of 7% for cofferdam corners and underwater joints, total procurement quantity: 963,000 m²
3. Functions & Performance of Geotextile
✅ Core Filtration + In-plane Drainage
It forms a filter layer between the drainage body and the silty fine sand of the embankment: allows seepage water to discharge freely while trapping sand particles, prevents fine soil from being washed away by seepage and eliminates piping risks. Meanwhile, it acts as an in-plane water-conducting layer to converge seepage water to the drainage prism behind the dam.
✅ Outcome: The cofferdam operates stably under high water level during flood seasons, with no sand loss or seepage failure. Smooth drainage effectively dissipates pore water pressure inside the embankment.
4. Construction Parameters
Laying: Manual laying underwater and on bank slopes during low-water season; relaxation rate: 2%～3%.
Overlap: Lay along the seepage direction, with the upstream geotextile overlapping the downstream one. Overlap width ≥30 cm on land and ≥50 cm for underwater sections.
Fixation: Ballasted by riprap and sand bags along edges. Sharp rock blocks are forbidden to fall directly onto the geotextile surface.
Quality control: The gradation of drainage rock behind the filter layer shall be strictly matched; the geotextile shall not be wrinkled or suspended.
5. Coordination with Other Measures
Geotextile: Filter barrier, retains soil and transmits water to prevent piping;
Drainage prism / rock fill drainage: Collects and discharges seepage water to reduce water head inside the dam;
Cofferdam fill soil: Main water-retaining structure;
Impervious inclined wall / partial geomembrane: Reduces total seepage flow.
