Overview
EN ISO 12958-1:2020 specifies a standardized index test for measuring the constant-head in-plane water flow capacity of geotextiles and geotextile-related products. The method determines the volumetric flow rate of water per unit width under defined normal compressive stresses and hydraulic gradients. This part (ISO 12958-1) is an index test intended for factory‑assembled products; full performance testing is covered separately in ISO 12958-2.
Key topics and technical requirements
- Test principle: constant-head measurement of water flow parallel to the plane of the specimen, reported as flow capacity (q_p_index) in (l/s)/m.
- Hydraulic gradients: apparatus must maintain head losses corresponding at least to hydraulic gradients of 0.1 and 1.0.
- Normal compressive stress: test applies controlled normal stresses; loading mechanism accuracy required to be within ±5% of the applied stress.
- Contact surface (boundary) types: three permitted contact configurations - foam/foam (F/F), rigid/foam (R/F), or rigid/rigid (R/R) - with specific foam and rigid liner requirements.
- Foam specification: recommended foam thickness linked to specimen thickness:
- up to 10 mm specimen → 10 mm foam each face
- 10–25 mm specimen → foam 1.0–1.25× specimen thickness
-
25 mm specimen → 25 mm foam each face
- two-layer foam allowed only when individual foam sheets exceed 10 mm
- Apparatus limits: discharge head must not exceed 100 mm; if average water head exceeds 100 mm and applied load ≤ 20 kPa, corrections to normal stress are required.
- Terminology: prefers term “water flow capacity” (accounts for non-laminar flow) rather than transmissivity which assumes laminar flow.
- Reporting and calculations: procedures for specimen selection, conditioning, measurement, conversions (e.g., temperature correction) and graphical representation are defined.
Applications and users
This standard is important for:
- Manufacturers of geotextiles and geocomposites - for factory quality control and product data sheets.
- Independent test laboratories - for reproducible index testing and comparative reporting.
- Design engineers and specifiers - to select materials with appropriate in-plane drainage capacity for applications such as drainage layers, landfill liners, road and railway substructures, and retaining structures.
- Regulatory bodies and procurement teams - for harmonized test evidence when assessing in-plane drainage performance.
Keywords: geotextiles, in-plane water flow, water flow capacity, index test, ISO 12958-1, constant-head, hydraulic gradient, geosynthetics.
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