Overview
EN ISO 12957-1:2018 - Geosynthetics: Determination of friction characteristics - Part 1: Direct shear test is a CEN-endorsed index test method that defines how to measure the frictional behaviour of geosynthetics in contact with a standard sand (EN 196-1), with specified density and moisture, using a direct shear apparatus. The procedure also permits testing with other soils, geosynthetic-to-geosynthetic interfaces and geosynthetic barriers under a controlled normal stress and constant displacement rate.
Key topics and requirements
- Scope and purpose: index test to determine friction characteristics (angle of friction, apparent cohesion/adhesion, shear stress) at geosynthetic/sand, geosynthetic/soil or geosynthetic/geosynthetic interfaces.
- Test specimens: sample preparation follows ISO 9862; minimum of four specimens per direction or face; specimen size must suit the apparatus.
- Conditioning: tests are performed in the standard atmosphere per ISO 554 - typically (20 ± 2) °C and (65 ± 2) % RH - until mass stabilisation (≤ 0.25 % change between readings).
- Apparatus: a constant contact-area direct shear box (upper/lower parts) with internal dimensions not less than 300 mm × 300 mm; box depth must accommodate sand layer/loading; for geogrids the box must include at least two full longitudinal ribs and three transverse bars in the tested length.
- Test principle: apply a constant normal force and shear the interface at a constant rate of displacement, recording shear force and displacement to derive shear stress, maximum shear stress and friction angle (best-fit regression).
- Measured outcomes:
- Angle of friction (ϕ) for sand/geosynthetic, soil/geosynthetic or geosynthetic/geosynthetic interfaces
- Apparent cohesion/adhesion (c_sg, a_gg)
- Friction ratio and shear stress parameters
- Calibration and limitations: results for geogrids against rigid supports can be influenced by support friction; calibration checks are recommended.
Applications and users
This standard is used to:
- Characterise interface friction for design of reinforced soils, retaining walls and slope stabilisation.
- Assess geosynthetic performance in landfill liners and geosynthetic barriers.
- Compare geotextile, geogrid and geomembrane interaction properties for product development and quality control.
Primary users:
- Geotechnical and civil engineers
- Materials and geosynthetics testing laboratories
- Manufacturers of geotextiles, geogrids and geomembranes
- Designers of soil reinforcement, retaining structures and containment systems
- Researchers studying interface mechanics
Related standards
- ISO 9862 - Sampling and preparation of geosynthetic test specimens
- ISO 554 - Standard atmosphere for testing
- EN 196-1 - Standard sand specification (referenced for standard sand properties)
- Other parts of the ISO 12957 series for complementary friction tests
Keywords: EN ISO 12957-1:2018, geosynthetics, direct shear test, friction characteristics, geotextiles, geogrids, geosynthetic barriers, standard sand, shear apparatus, angle of friction.