Overview
ISO 17892-7:2017 defines the laboratory method for the unconfined compression test used in geotechnical investigation and testing of soil. The standard specifies how to prepare homogeneous specimens (undisturbed, re‑compacted, remoulded or reconstituted), the required apparatus and measurement accuracy, the test procedure (including strain rate and data recording), and how to report results. The test provides the unconfined compressive strength and an estimate of undrained shear strength for soils that behave sufficiently undrained during loading (typically low‑permeability soils). ISO 17892-7:2017 also fulfils requirements of EN 1997‑1 and EN 1997‑2.
Key topics and technical requirements
- Scope and applicability: Method applies to homogeneous soil specimens under axial compression; drainage is not prevented, so undrained shear strength estimates are only valid when soils remain effectively undrained during the test.
- Apparatus: Load frame with smooth, non‑vibratory platen movement; top/bottom platens with negligible deformation; alignment maintained.
- Measuring accuracy: Load device accuracy ~2% (20–100% range); displacement device accurate to 0.1 mm or 0.1% of initial height.
- Specimen dimensions: Specimens may be circular or square with defined height‑to‑diameter (or side) ratios and particle‑size limits (largest particle should not exceed 1/6 of specimen width).
- Test procedure: Strain rate between 1% and 2% of specimen height per minute; record load, displacement and time frequently (minimum readings before and after failure); stopping criteria include strain thresholds or post‑peak stress reduction.
- Results & reporting: Calculate bulk/dry density, water content, stress–strain behaviour, unconfined compressive strength and derived undrained shear strength (cu = ½ qu). Calibration, maintenance and checks are covered in Annex A.
Practical applications and users
- Applications:
- Rapid assessment of soil strength for site characterization and preliminary design.
- Estimation of undrained shear strength for cohesive, low‑permeability soils.
- Quality control for re‑compacted samples and laboratory specimen preparation.
- Who uses it:
- Geotechnical and civil engineers, laboratory technicians, consultants, researchers and contractors performing soil testing or preparing geotechnical design parameters.
- Organizations complying with EN 1997 (Eurocode 7) or following ISO laboratory testing best practice.
Related standards
- ISO 17892 series (laboratory testing of soil) - see Parts 1 (water content) and 2 (bulk density).
- ISO 14688‑1 (soil identification and description).
- EN 1997‑1 / EN 1997‑2 (Eurocode 7 requirements referenced by this document).
Keywords: ISO 17892-7, unconfined compression test, geotechnical testing, unconfined compressive strength, undrained shear strength, soil laboratory testing, specimen preparation, strain rate, load frame.