ISO 22476-11:2017

Overview - ISO 22476-11:2017 (Flat dilatometer test, DMT)

ISO 22476-11:2017 specifies requirements for performing and reporting the flat dilatometer test (DMT) as part of geotechnical investigation and field testing. The standard covers equipment, test procedure, membrane calibration, data acquisition and reporting. It fulfils flat dilatometer test requirements for geotechnical investigations in accordance with EN 1997‑1 and EN 1997‑2.

The DMT involves vertically inserting a blade-shaped steel probe with a thin circular steel membrane and recording two key pressures as the membrane expands: the pressure at 0.05 mm centre deflection (A‑pressure) and at 1.10 mm (B‑pressure), plus a controlled rebound pressure (C‑pressure). Typical sounding depth increments are 100–300 mm.

Key topics and technical requirements

• Equipment: dilatometer blade and membrane, control & calibration unit, pressure source, pneumatic‑electrical cable, earth wire, calibration syringe; optional automated data acquisition and load cell.
• Membrane and blade: blade dimensions, membrane mounting and penetrating edge geometry are specified; membrane calibration before and after testing is required.
• Pressure measurements:
  • A‑pressure (0.05 mm) and B‑pressure (1.10 mm) detections via internal switch mechanism;
  • C‑pressure measured during controlled deflection recovery.
• Control unit features: earthing socket, controlled gas flow/venting, signal detection for switch activations, pressure measurement with reproducibility (2.5 kPa for <500 kPa) and gauges with ≥0.50% accuracy.
• Data acquisition (if used): transducer linearity/hysteresis ≤ ±0.50%, ≥14‑bit ADC, acquisition frequency ≥50 Hz.
• Insertion apparatus: thrust machine (e.g., CPT/CPTU rigs), straight push rods (commonly 1 m), hollow/slotted adaptors for cable exit, and friction reducers to minimise rod friction.
• Test procedure: pre‑test checks, membrane calibration, basic sounding sequence, dissipation tests (DMTA, DMTA‑s), safety measures, and detailed reporting of results.

Applications and practical value

• Soil stratigraphy mapping - high‑resolution vertical profiling for clays, silts and sands.
• In situ stress & deformation - assessment of horizontal stress index (KD), dilatometer modulus (ED) and material index (ID).
• Shear strength estimation and detection of slip surfaces in clays.
• Ground characterization for foundation design, slope stability, consolidation studies and numerical modelling.

Who uses ISO 22476-11

• Geotechnical engineers and site investigation specialists
• Geotechnical consultants and contractors performing in situ testing
• Design engineers using DMT-derived parameters for foundation and slope designs
• Research labs developing or validating field test methods

Related standards

• ISO 22476 series (other field tests)
• ISO 22476‑1:2012 (CPT/CPTU references)
• EN 1997‑1 and EN 1997‑2 (Eurocode 7 geotechnical design)

Keywords: ISO 22476-11, flat dilatometer test, DMT, geotechnical investigation, in situ testing, A‑pressure, B‑pressure, C‑pressure, soil stratigraphy, dilatometer modulus.