Overview
EN ISO 22476-3:2005 - "Geotechnical investigation and testing - Field testing - Part 3: Standard penetration test (SPT)" is a CEN-endorsed ISO standard that specifies requirements for performing the Standard Penetration Test as part of geotechnical investigations in accordance with EN 1997-1 and EN 1997-2. The standard defines equipment, test procedure, measurement and reporting rules for indirect soil investigation by SPT to complement direct sampling (e.g., EN ISO 22475-1).
Key topics and requirements
- Purpose and scope: Measures resistance of soil at the borehole base to dynamic penetration of a split-barrel sampler (SPT) and recovers disturbed samples for identification. Also covers SPT(C) using a solid cone in gravelly soils or soft rock.
- Test basics: Use of a 63.5 kg hammer dropped 760 mm to drive the sampler. The N‑value is the number of blows required to drive the sampler 300 mm after a 150 mm seating drive.
- Equipment:
- Split-barrel sampler with non-return valve and specified dimensions.
- Drive rods with stiffness to prevent buckling (straight rods, mass limit noted).
- Drive-weight assembly (hammer, guide, anvil/drive head, automatic release) with overall mass limit and controlled free-fall.
- Optional blow counters and displacement/penetration sensors.
- Calibration and energy: The standard requires determination and reporting of the energy ratio (Er) - actual energy delivered vs theoretical hammer energy - because N-values depend on equipment energy. Annex B gives a recommended method to measure actual energy; Annex A lists correction factors (rod length, energy losses, overburden effects).
- Procedure and safety: Borehole preparation, seating drive, test drives (minimum two increments of 150 mm), termination rules (e.g., stop at 50 blows for the 300 mm test, 100 blows in soft rock). Mandatory checks, periodic rod straightness verification, and adherence to national safety regulations.
- Reporting: Comprehensive field report requirements including project ID, borehole coordinates, equipment details (manufacturer, hammer type, rod type), calibration certificate for Er, raw and corrected N-values, and sampling records.
Applications and users
- Primary users: Geotechnical engineers, site investigation contractors, foundation designers, and laboratories performing in-situ testing.
- Typical uses:
- Assessing strength and deformation properties of cohesionless soils.
- Ground characterization for foundation design, earthworks, and excavation stability.
- Providing N‑values for correlation with soil parameters, settlement estimates, and design checks.
- Complementary role: Used alongside sampling standards (EN ISO 22475-1) and other in-situ tests (cone penetration, pressuremeter tests) to form a complete ground model.
Related standards
- EN 1997-1 / EN 1997-2 (geotechnical design and investigations)
- EN ISO 22475-1 (sampling by drilling and excavation methods)
- Other parts of EN ISO 22476 series covering alternative field tests (cone, pressuremeter, dilatometer)
Keywords: EN ISO 22476-3:2005, Standard Penetration Test, SPT, N‑value, geotechnical investigation, field testing, energy ratio, split-barrel sampler.
