Overview
ISO 12957-2:2005 specifies the inclined plane test for determining the friction characteristics of geosynthetics (geotextiles, geogrids, geosynthetic barriers) in contact with soils at low normal stress. The method is primarily a performance test using site‑specific soils but can also be used as an index test with standard sand. The test measures the angle at which a soil‑filled box slides over a geosynthetic as the supporting plane is slowly inclined.
Key topics and technical requirements
- Test principle: Tilt an inclined plane at a controlled rate and record the angle of slipping (β) when the upper soil box displaces 50 mm. Angle of friction (φgp) is derived from repeated runs.
- Normal stress: Standard normal stress applied is (5 ± 0.1) kPa; even pressure distribution is required (rigid plate or fluid membrane).
- Apparatus types:
- Rigid base apparatus (geosynthetic supported on a smooth plate).
- Soil‑filled base apparatus (geosynthetic supported by a lower soil box).
Note: Results for geogrids tested on a rigid support may not be realistic because outcomes depend on the friction support.
- Control and measurement:
- Inclination rate typically (3 ± 0.5)°/min.
- Angle measurement precision ±0.5°.
- Displacement measured to ±0.05 mm, readings ≤30 s intervals.
- Upper box displacement stop at 50 mm.
- Specimen preparation and conditioning:
- Sample cutting and preparation per ISO 9862.
- Condition in standard atmosphere per ISO 554 (20 ±2 °C, RH 65 ±2 %) until mass stabilizes.
- Apparatus dimensions and gaps: Minimum upper box ~300 × 300 mm; soil depth H > 7× maximum particle size and gap between box base and geosynthetic 0.5–1.5 mm.
- Calibration: For roller‑supported boxes, calibrate to ensure roller friction is negligible and quantify restraining force for calculations.
Practical applications
- Assess interface friction for design of reinforced soil structures, slopes, retaining walls and landfill liners.
- Provide input parameters for geotechnical stability analyses (e.g., design friction angles between geosynthetics and in‑situ soils).
- Quality control and product development testing for geosynthetic manufacturers and testing laboratories.
- Comparative index testing using standard sand to track material changes or batch consistency.
Who should use this standard
- Geotechnical and civil engineers designing reinforced soil systems
- Geosynthetic manufacturers and R&D teams
- Construction contractors performing site acceptance tests
- Independent testing laboratories and accreditation bodies
- Researchers studying interface behavior of geosynthetics
Related standards
- ISO 12957-1 - Direct shear test (complements inclined plane method)
- ISO 554 - Conditioning atmosphere for tests
- ISO 9862 - Sampling and specimen preparation
- ISO 6344-2 - Abrasive grain size (used for emery cloth supports)
Keywords: geosynthetics, inclined plane test, friction characteristics, geotextiles, geogrids, geosynthetic barriers, standard sand, interface friction.
Open preview (PDF)Geosynthetics — Determination of friction characteristics — Part 2: Inclined plane test