Overview
EN ISO 12956:2020 (identical to ISO 12956:2019) specifies a laboratory wet‑sieving test method to determine the characteristic opening size of a single layer of geotextiles and geotextile‑related products. The characteristic opening size (commonly noted as O90) is defined by the particle size of a granular test material that passes through the geotextile such that 90% of the passing mass is finer than that particle size. This standard supersedes EN ISO 12956:2010 and is published by CEN/ISO for geosynthetics testing.
Key topics and technical requirements
- Test principle: wet sieving of granular material through a clamped geotextile specimen; O90 is derived from the passing granular particle size distribution.
- Apparatus essentials:
- Sieving unit with vertical motion at 50–60 Hz and 1.5 mm amplitude (3 mm swing height); minimum exposed sieving diameter 130 mm.
- Water supply and spray nozzle(s) enclosed to prevent material loss; recommended flow approx. 0.5 L/min at ~300 kPa with a flow regulator.
- Support grid (mesh 10 ± 1 mm, wire 1–2.5 mm) to avoid specimen deformation and a sealed cover to prevent leakage.
- Filter paper (max opening 10 µm), balance with max error 0.03 g, and oven up to 110 °C.
- Granular material: cohesion‑less, essentially round particles (e.g., glass beads) with controlled gradation and a coefficient of uniformity Cu between 3 and 20; Annex B provides guidance and optimisation curves for selecting gradation to improve accuracy.
- Specimens: cut five test specimens per sample; handle flat and avoid folding; specimen selection and preparation per ISO 9862.
- Documentation: test procedure, calculations, and reporting requirements are specified (including annexes for mesh sizes, worked example, and knitted tubular preparation).
Applications and users
- Practical uses: selection and quality control of geotextiles for filtration, drainage, separation and erosion control, where pore/opening size influences soil retention and hydraulic performance.
- Typical users: geotechnical and civil engineers, geosynthetic manufacturers, independent testing laboratories, specifications writers, and contractors involved in drainage and earthworks projects.
Related standards
- ISO 9862 - Sampling and preparation of test specimens (normative reference)
- ISO 10320 - Identification on site (normative reference)
- EN ISO 12956:2020 replaces the 2010 edition; consult annexes (A–C) for mesh sizes, examples, and preparation guidance.
Keywords: EN ISO 12956:2020, ISO 12956:2019, geotextiles, characteristic opening size, O90, wet‑sieving, geosynthetics, filtration test, test method.
