ISO 12957-1:2018

Overview

ISO 12957-1:2018 - Geosynthetics - Determination of friction characteristics - Part 1: Direct shear test - specifies an index laboratory method to measure the friction behaviour of a geosynthetic in contact with a standard sand (EN 196-1) using a direct shear apparatus. The procedure also applies to geosynthetic‑to‑soil and geosynthetic‑to‑geosynthetic interfaces and can be used for testing geosynthetic barriers. The standard defines specimen sampling, conditioning, apparatus types, test procedure, calculations (angle of friction, apparent cohesion/adhesion, friction ratio) and reporting requirements.

Key topics and technical requirements

• Test principle: shearing a geosynthetic at a controlled displacement rate under defined normal stresses to obtain shear stress vs. displacement and derive the angle of friction (ϕ) and related parameters.
• Reference materials: standard sand grading per EN 196-1 and conditioning in the standard atmosphere per ISO 554. Sampling follows ISO 9862.
• Specimens: four test specimens per direction (and per face if surfaces differ); specimen size must suit apparatus.
• Apparatus: constant contact‑area or reducing contact‑area direct shear boxes (minimum internal size commonly 300 × 300 mm). Requirements include rigid supports, carriage with low‑friction bearings, and an appropriate gap for sand dilatation.
• Loading and rates: horizontal shear at a constant rate of (1 ± 0.2) mm/min as standard; for low‑permeability soils (particle size d < 0.0075 mm) drained conditions may require much lower rates (0.005–1.0 mm/min). Normal load and shear force measurement accuracy typically ±2%; displacement accuracy ±0.02 mm.
• Data and checks: measure internal angle of friction of the sand (or soil), monitor sand grading and moisture (loss on drying < 0.2 %; moisture additions up to 2 % permissible to prevent segregation), and verify calibration when rigid supports affect results (e.g., geogrids).

Applications and users

ISO 12957-1:2018 is used to provide comparative friction parameters for design and quality control in:

• reinforced soil structures (retaining walls, reinforced slopes),
• landfill and containment systems (interfaces with liners and geosynthetic barriers),
• pavement and subgrade reinforcement,
• product development and performance verification by geosynthetic manufacturers,
• geotechnical laboratories undertaking interface testing,
• researchers and regulators requiring standardized friction data.

Users: geotechnical engineers, laboratory technicians, product designers, testing labs, and standards bodies.

Related standards

• ISO 9862 - Sampling and preparation of geosynthetic test specimens
• ISO 554 - Standard atmosphere for conditioning and testing
• EN 196-1 - Specification for the standard sand used in this test
• Other parts of the ISO 12957 series (see ISO catalogue)

Keywords: ISO 12957-1:2018, geosynthetics, direct shear test, friction characteristics, EN 196-1, geogrids, geotextiles, geosynthetic barriers, shear apparatus, angle of friction.