Overview
EN ISO 12957-2:2024 - Geosynthetics: Determination of friction characteristics (Inclined plane test) specifies a laboratory method to determine the friction behaviour of geosynthetics (geotextiles, geotextile-related products and geosynthetic barriers) when in contact with soils or another geosynthetic under low normal stress. Adopted by CEN as EN ISO 12957-2:2024, this test is primarily a performance test using site‑specific soils but can be used as an index test with standard sand. The method can also capture time‑dependent displacement (creep) of the interface without necessarily reaching slippage failure.
Key topics and technical requirements
- Test principle: a specimen supported on an inclining plane is gradually tilted; the angle of slipping (β) is recorded when the upper box displacement reaches 50 mm. The measured angle is used to calculate the angle of friction (φ) and interface shear behaviour.
- Normal force / stress: definitions and calculation of normal force (N) and normal stress (σn) are included; tests are performed at low normal stress to reflect common field conditions.
- Apparatus types: requirements for both rigid‑base apparatus and soil‑filled base apparatus are described (upper and lower boxes, roller support options). Note: test data from geogrids on rigid supports can be dependent on the support friction and may not be realistic.
- Specimen preparation and number: sampling and preparation follow ISO 9862; three specimens per direction are typical, sized to suit the apparatus.
- Measurements and calculations: procedures cover measurement of restraining force for empty boxes fr(β), shear stress (τ) and calibration of the apparatus; creep (displacement over time) can be measured as an alternative outcome.
- Conditioning and calibration: environmental conditioning per ISO 554 and calibration procedures are specified to ensure reproducible results.
Practical applications and users
- Design and verification: geotechnical and civil engineers use results for interface design in reinforced slopes, retaining walls, embankments, landfill lining systems and erosion control.
- Product development and QC: manufacturers of geotextiles, geogrids and geosynthetic barriers use the test for product evaluation, performance claims and quality control.
- Construction and testing laboratories: independent testing labs and contractor testing teams perform the inclined plane test to validate site‑specific interface behaviour with native soils.
- Specification writers and standards committees: use test outputs for contract specifications and performance criteria.
Related standards
- ISO 9862 - Sampling and preparation of test specimens
- ISO 10318-1 - Geosynthetics terms and definitions
- ISO 554 - Standard atmospheres for conditioning/testing
- ISO 6344-2 - (Referenced for abrasive grain sizes where applicable)
Keywords: geosynthetics, inclined plane test, friction characteristics, EN ISO 12957-2:2024, geotextiles, geogrids, interface friction, angle of slipping, creep, site-specific soils.
