Overview
EN ISO 11276:2014 (identical to ISO 11276:1995) is a CEN/ISO standard for soil quality that specifies the tensiometer method for determination of pore water pressure in both unsaturated and saturated soils. It covers point measurements using tensiometers for in situ field work and laboratory/experimental setups such as soil cores and plant containers. The standard describes instrument components, installation, calibration, limitations and maintenance to obtain reliable pore water pressure data.
Key topics and technical requirements
- Scope & limits
- Applicable to pore water pressures down to about –85 kPa at normal atmospheric pressure; reduced range at lower atmospheric pressures.
- Tensiometers do not function if sub-zero temperatures occur at measurement depth.
- Principle
- A porous cup filled with de-aired water equilibrates with soil water; the internal water pressure (corrected for height differences) equals local pore water pressure (matric + pneumatic).
- Tensiometer construction
- Porous cup (typically unglazed ceramic or alternative materials described in annexes) must be air-entry rated and durable in soil.
- Connecting/body tubes of low permeability with leakproof joints; minimize number of joints.
- Pressure sensors: mercury manometers, Bourdon gauges, and electrical pressure transducers are described; sensor accuracy determines measurement accuracy.
- Installation & measurement
- Install vertically or horizontally with porous cup centered at desired depth while minimizing soil disturbance and ensuring good cup-soil contact.
- Use replicate tensiometers to capture spatial variability.
- Calibration, servicing & maintenance
- Use de-aired water (boiled or vacuum-degassed) and avoid entrapped air when filling.
- Regular servicing is required to remove air accumulation (air-trap limit: >100 mm3 requires refilling).
- Verify accuracy of Bourdon gauges and transducers before installation and at least annually; test assemblies for leaks under pressure/vacuum.
- Units & conversions
- Uses SI units (Pascal) and provides conversions between soil water potential, pressure and head equivalents.
Applications and users
- Practical uses:
- Monitoring soil moisture tension for agronomy, irrigation scheduling and greenhouse management.
- Geotechnical and environmental investigations (slope stability, unsaturated soil mechanics).
- Laboratory testing of soil cores, lysimeters and experimental soil columns.
- Typical users:
- Soil scientists, agronomists, geotechnical engineers, environmental consultants, laboratory technicians and researchers working with soil testing, pore water monitoring and instrumentation.
Related standards
- Adopted by CEN as EN ISO 11276:2014 from ISO 11276:1995 (prepared by ISO/TC 190, Soil quality). For broader context, consult other ISO/CEN soil quality standards and CEN/TC 345 guidance on soil characterization.
Keywords: soil quality, pore water pressure, tensiometer method, EN ISO 11276:2014, in situ measurements, unsaturated soil, soil cores, soil testing.