Geotechnical Guidance

AGS Guide to the Selection of Geotechnical Pressuremeter Testing

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Published April 2024

Pressuremeter testing (PMT) is a recommended in situ testing technique for ground investigation, referenced in Eurocode 7 (EN 1997-2). “The objective of a pressuremeter test is to measure the in situ deformation of soils and rocks by the measured expansion of a cylindrical pressurised membrane” (EN 1997-2).

Pressuremeters are typically used to provide in situ stress, strength and stiffness parameters of soils and rocks. This type of testing can provide high quality information since disturbance to the in situ ground state is minimised, particularly when compared to samples removed for geotechnical laboratory testing.

The acronym ‘PMT’ covers a range of equipment types which vary in complexity and sophistication that can operate in different ground conditions, providing information on ground properties. The testing procedure and instrumentation is generally complex and operated by specialist engineers and contractors. Testing is carried out in accordance with the relevant sections of BS EN ISO 22476, and procedures vary depending on the type of equipment deployed.

All pressuremeters are deployed downhole and a test is undertaken by applying a load to generate radial displacement at the borehole wall (except for flat dilatometers). Both the load and displacement are recorded throughout the test. The varying load is dictated by the pressure within the probe itself.

The change in pressure and resulting movement at the borehole wall illustrate a cavity expansion with an increase in cavity strain. Solutions of varying complexity can be applied to determine engineering parameters, such as stiffness and strength. It is possible to avoid empiricism, depending on the specific pressuremeter used. The type of test itself may vary depending on factors such as number of unload/reload cycles, and the addition of creep holds. Furthermore, the insertion technique, as well as the approach to applying the load, dictate the quality of the test.