Overview
ISO 22476-3:2005 - "Geotechnical investigation and testing - Field testing - Part 3: Standard penetration test" provides standardized requirements for performing the Standard Penetration Test (SPT) as part of geotechnical site investigation. The document defines equipment, test procedure, results reporting and quality checks to ensure consistent measurement of penetration resistance (the N-value) used to assess soil strength and deformation properties. The standard is intended to complement direct investigations and sampling (for example, per EN 1997 and ISO 22475-1).
Key topics and technical requirements
- Purpose: Measure resistance of soil at the borehole base to dynamic penetration of a split-barrel sampler (SPT) and recover disturbed samples. A solid cone may be used in gravelly soils (noted as SPT(C)).
- Test fundamentals: Driving a sampler with a 63.5 kg hammer dropped from 760 mm; seating drive of 150 mm followed by a 300 mm test drive to obtain the N-value (number of blows for 300 mm penetration).
- Equipment requirements:
- Drive-weight assembly mass limit (overall ≤115 kg) and hammer mass tolerance (63.5 kg ±0.5 kg).
- Drive rods straightness, stiffness and mass limits (no more than 10.0 kg/m; relative deflection ≤1:1 200).
- Split-barrel sampler dimensions, non-return valve and optional solid cone for SPT(C).
- Quality control and calibration:
- Pre-test checks of height of fall, release mechanism and anvil; routine calibration of measuring instruments.
- Energy ratio (E_r): actual energy delivered versus theoretical energy; calibration and certificate required for quantitative use. Annex B describes measuring actual energy; Annex A lists correction factors.
- Procedure and safety:
- Borehole preparation and clean base required; rules for testing below groundwater table.
- Limits on maximum blows (typically stop at N = 50; soft rock up to N = 100).
- Reporting requirements and field log details.
Applications
- Foundation design input: estimating strength and stiffness of cohesionless soils.
- Site investigation and ground characterization for buildings, earthworks, roads, and shallow foundations.
- Preliminary ground appraisal and correlation with other in-situ tests (CPT, dynamic probing).
- Comparable baseline for construction contractors, geotechnical consultants and forensic investigations.
Who uses this standard
- Geotechnical engineers and engineering geologists
- Site investigation contractors and drilling crews
- Design consultants, laboratory personnel and regulators enforcing EN 1997 compliance
Related standards
- EN 1997-1 / EN 1997-2 (Geotechnical design and investigations)
- ISO 22475-1 (Sampling by drilling and excavation methods)
- Other parts of ISO 22476 (e.g., cone, dynamic probing, pressuremeter methods) for complementary field tests
Keywords: ISO 22476-3:2005, standard penetration test, SPT, N-value, geotechnical investigation, drive rods, energy ratio, EN 1997.
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