ISO 22476-7:2012

Overview

ISO 22476-7:2012 - Borehole jack test defines the equipment, execution and reporting requirements for conducting borehole jack tests as part of geotechnical investigation and field testing. The standard specifies the procedure for placing a diametral borehole jack in a pocket, hydraulically expanding two diametrical steel loading plates, and measuring the applied pressure and associated opening to obtain a stress–displacement relationship for the ground. It applies to test depths of ≤ 100 m and to both on‑shore and off‑shore investigations.

Key topics and technical requirements

• Scope and purpose
  • Tests carried out in ground stiff enough not to be adversely affected by drilling.
  • Results used for ground deformation calculations when test stress range matches expected design stresses.
• Equipment (obligatory and recommended)
  • Obligatory: borehole jack, hydraulic pump, pressure line, pressure gauge, measuring unit, signal cable.
  • Recommended: sediment collection tube, setting rods.
  • Transducers in the instrument measure hydraulic pressure and loading‑plate expansion; multiple displacement transducers are required if plates can tilt.
• Pocket drilling and device placement
  • Recover a sample at the test depth (per ISO 22475-1) before testing.
  • Use casing if borehole instability is expected; core a pocket (about 3 m length) and set the jack with minimal disturbance.
  • Positioning checks: upper edges of plates ≥ 0.5 m from pocket entry and lower edges ≥ 0.5 m from pocket bottom.
• Calibration and measurement control
  • Calibrate displacement and pressure measuring systems before testing; document calibrations and verify after repairs (see Annex B).
• Loading programme and test sequences
  • Select maximum hydraulic pressure considering expected structural loads.
  • Two main approaches: load/unload/reload loops (minimum three unload/reload loops during loading) or tests designed for time‑dependent behaviour.
• Test results and reporting
  • Record stress–displacement data, basic equations and test corrections; present results with appropriate axis scaling and uncertainty information (Annexes C–F provide examples and guidance).

Practical applications and users

Who uses it:

• Geotechnical engineers, site investigation teams, foundation and geotechnical design consultants, marine/offshore geotechnical specialists, and testing contractors.

Typical uses:

• Determining ground stiffness and deformation properties for foundation design.
• Supplementing classification and sampling (ISO 22475-1; ISO 14688 / 14689) to assess load–deformation behavior for geotechnical design compliant with EN 1997‑1/‑2.

Related standards (selected)

• ISO 22476 series (other field tests: CPT, pressuremeter, dilatometer, vane, etc.)
• ISO 22475-1 (sampling)
• ISO 14688-1, ISO 14689-1 (soil/rock ID and classification)
• ISO 10012; ISO/IEC Guide 98-3 (measurement management and uncertainty)
• EN 1997 (Eurocode 7) - referenced for geotechnical investigation requirements

Keywords: ISO 22476-7:2012, borehole jack test, geotechnical investigation, field testing, stress‑displacement relationship, calibration, loading programme, ground deformation, test depths ≤ 100 m.