ISO 18674-3:2017

Overview

ISO 18674-3:2017 defines how to measure displacements across a line using inclinometers for geotechnical monitoring. It sets out the principles for instrumentation, installation, measurement, data processing and reporting used to monitor ground movement, structures interacting with the ground and geotechnical works. The standard complements the general rules in ISO 18674‑1 and, together with ISO 18674‑2, enables determination of displacements in any direction.

Key topics and technical requirements

• Inclinometer types: distinction between probe inclinometers (traversing probes moved stepwise in a guide tube) and in-place inclinometers (IPI) (sensors fixed in-place or in elements).
• Sensor configurations: uniaxial (single plane) and biaxial (two perpendicular planes) tilt sensors; planes A and B are defined and marked on instruments.
• Inclinometer casing and guide tubes: requirements for guide tube installation, keyways, securing in boreholes or cast-in-place concrete.
• Measurement procedure: use of a reference measurement and subsequent follow-up readings; displacements are deduced by comparing tilt changes (see Annex A for evaluation procedures).
• Gauge length and base length: definitions and typical values (gauge length commonly 0.5 m or 1.0 m for probe inclinometers).
• Accuracy and repeatability: instruments, depth-marking and calibration checks are required to ensure reliable results.
• Limitations: for vertical measuring lines inclinometers can resolve two lateral components; for horizontal lines they measure the vertical component only. Deflectometers (Annex B) can supplement inclinometers to capture horizontal displacements on horizontal lines.
• Documentation: installation reports and monitoring reports with data processing, evaluation and interpretation requirements.

Applications and users

ISO 18674-3 is applicable to:

• Monitoring natural slopes, embankments, excavation walls, foundations, dams, tunnels and refuse dumps.
• Checking geotechnical designs under the Observational Design approach.
• Deriving geotechnical parameters from load tests or trial tunnelling.
• Identifying active shear planes and tracking subsurface movement.

Typical users:

• Geotechnical engineers and consultants
• Instrumentation specialists and field technicians
• Civil and tunnel contractors
• Surveyors and monitoring programme managers
• Researchers conducting ground movement studies

Related standards

• ISO 18674-1: General rules for geotechnical monitoring
• ISO 18674-2: Extensometers (displacements along a line)
• ISO 22475-1: Sampling and groundwater measurement principles

Keywords: ISO 18674-3:2017, geotechnical monitoring, inclinometers, displacement measurement, probe inclinometer, in-place inclinometer, inclinometer casing, deflectometer, gauge length, biaxial inclinometer.