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.
Open preview (PDF)Geotechnical investigation and testing — Field testing — Part 7: Borehole jack test