ISO 22476-16:2024

Overview - What ISO 22476-16:2024 covers

ISO 22476-16:2024 specifies the borehole shear test using the phicometer procedure (commonly called the phicometer or PBST). It defines equipment, execution and reporting for in situ determination of soil shear strength parameters - notably the friction angle (φ) and cohesion (c) - for borehole tests carried out to a maximum depth of 30 m. The standard applies to most natural soils, fills and engineered soils (saturated or unsaturated), with stated exclusions (very soft fine soils, very loose coarse soils, medium‑strong to very‑strong rock, and soils dominated by cobbles >150 mm). Typical representativeness ranges are given (approximate in‑situ resistance indicators: Ménard limit pressure ≈ 0.4 MPa; CPT cone resistance ≈ 1.5 MPa; SPT N ≈ 8).

Key technical topics and requirements

• Test principle: Expandable phicometer probe is pressed against the borehole wall, teeth engage the soil, and axial displacement produces shear while normal pressure is controlled in stages.
• Equipment: Probe geometry and shearing-zone dimensions, connection tubing, pulling rods, surface pulling device, pressure–volume control unit, and measurement systems for time, pressure, volume, pulling force and axial displacement.
• Procedure: Pre‑checks, borehole drilling and probe placement, teeth insertion, multi‑stage shearing under controlled pressure holds, and end‑of‑test procedures.
• Data and analysis: PBST shearing curves, adjustment procedures to derive in situ φ and c (Clause 8), associated graphs and validation of representativeness of results.
• Quality & compliance: Calibration, equipment checks, accuracy/uncertainty guidance, reporting templates (field report, test report, logs) and safety requirements.
• Normative/Informative annexes: Probe characteristics, calibration/corrections, execution guidance, determination examples and accuracy assessments.

Practical applications and users

ISO 22476-16 is intended for geotechnical engineers, site investigation teams, consultants, contractors and testing laboratories performing field testing to obtain shear strength parameters where sampling is difficult or disturbed. Typical applications:

• Evaluating soil strength for foundation and slope stability assessments
• Input for earthworks and retaining structure design where in situ shear parameters are required
• Supplementing laboratory tests when representative sampling is not feasible

The PBST/phicometer test provides direct in situ shear measurements that complement CPT, SPT and pressuremeter data.

Related standards

• ISO 22476 series (other parts covering field testing methods) and national standards where the PBST has been previously standardized. ISO 22476-16 was developed in collaboration with CEN/TC 341 (Geotechnical investigation and testing).

Keywords: ISO 22476-16:2024, phicometer test, PBST, borehole shear test, in situ shear strength, friction angle φ, cohesion c, geotechnical investigation.